HVAC Environmental Sealing & Venting
H-O Products die-cuts and converts rooftop-unit door and access-panel gaskets, controls-cabinet enclosure gaskets, roof-curb seals, duct-flange and plenum gaskets, pressure-equalization vent parts, and filter-rack seals into the environmental-sealing material set on packaged HVAC equipment, built to your drawing.
Built for: packaged rooftop units and air handlers, condensing units and chillers, furnace and controls compartments, duct and plenum connections commonly framed by SMACNA duct-construction practice, and enclosure designs commonly evaluated to NEMA 250 and IEC 60529 ratings at the tested-enclosure level.
To seal a packaged HVAC unit, work the six sealing points from the outside in. Doors and access panels: die-cut RE-series EPDM foam perimeter gaskets (compression classes per ASTM D1056 on the grade TDSs; EPDM is commonly specified for UV and ozone exposure), with BISCO® HT-870-class cellular silicone where temperature endurance or a flame class drives the choice. Controls cabinet: PORON® 4701-series microcellular urethane gaskets (methods per ASTM D3574.
The remaining zones and duties are mapped in the When-to-spec list on this page. Values are per the TDS on file.
System-level, by designation (the rating or leakage class belongs to the tested enclosure or duct system): NEMA 250 (enclosure types) · IEC 60529 (IP code) · SMACNA duct-construction and air-leakage practice · AHRI equipment-rating frameworks as design context. Material-level, per the vendor TDS: UL 94 (flammability classes, incl.
V-0 on the rated grades) · ASTM D1056 (cellular rubber compression classes: EPDM, neoprene, vinyl nitrile) · ASTM D3574 (flexible cellular polyurethane methods: PORON®, filter foam) · ASTM E84 (surface burning characteristics, where reported per grade).
- RTU door & panel gaskets: RE-series EPDM foam / 553 solid EPDM
- Hot-section gaskets & flame-class duty: BISCO® cellular silicone
- Controls-cabinet gaskets: PORON® 4701 series (40V0 for V-0 duty)
- Roof-curb seals: vinyl nitrile foam / SCE42B neoprene
- Duct-flange gaskets: neoprene sponge + EPDM sponge
- Vent ports & louvers: membranes per vendor TDS + reticulated foam
- Filter-rack & wipe seals: F-1 / F-10 pressed felt
- Low-closure-force joints: BISCO® BF-1000 Extra Soft
Where are you in the spec process?
This page serves engineers who already know the gasket or vent part they want and engineers still walking the unit panel by panel. Pick the path that matches where you are; you don't have to read the rest.
Send a drawing, get a quote
A door-perimeter gasket, a controls-cabinet gasket, a curb-seal strip set, a duct-flange gasket, a vent-port part, a filter-rack seal, or a complete per-unit sealing kit on your drawing.
Skip to the quote form →Walk the six sealing points job by job
Six numbered jobs (doors, cabinet, curb, duct, vent, filter rack), a sealing-point checklist builder, and seven material families with TDS-cited methods and by-designation standards language.
Start with job 1 →
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1Send drawingUpload a DXF, STEP, or PDF, or describe the panel, cabinet, curb, or duct joint. A sample part works too.
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2Material reviewEngineering reviews gap ranges, closure forces, weather and temperature exposure, and any flame-class requirement against the vendor TDSs, and frames the standards language correctly: material classes (UL 94) per TDS, enclosure and duct frameworks (NEMA 250, IEC 60529, SMACNA) by designation.
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3PrototypeSamples typically ship in 3–5 business days for common configurations on materials we keep on hand. Made-to-order; MOQ varies by material and part.
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4ProductionStandard production runs ship about 2 weeks after drawing approval, on flatbed die-cutting, CNC knife cutting for kiss-cut gasket sets, slitting for curb and flange strip stock, waterjet cutting for thick sections, and kitting for per-unit gasket kits. Ongoing parts run with material traceability and lot-code TDS records.
Which sealing point are you closing?
The six sealing and venting jobs, zone by zone
Pick a zone to see the job, the materials that lead it, and what to put on the drawing.
Rooftop-unit door & access-panel gaskets
A packaged rooftop unit is a sheet-metal box that service technicians open in every season and the weather works on every day in between. Its hinged doors and lift-off access panels close on perimeter gaskets that do three jobs at once: keep wind-driven rain out of the blower and controls sections, keep conditioned air from leaking past the panel flange, and absorb the panel rattle a running blower would otherwise turn into noise.
The gasket sees UV, ozone, and temperature swings on the outside face and compression cycling from every latch on the inside, and it has to keep sealing after years of both.
What H-O converts. Die-cut perimeter gaskets, slit strips, and corner-spliced gasket sets from RE-series EPDM foam (RE41E through the firmer grades, compression classes per ASTM D1056 on the grade TDSs) and EPDM sponge, with 553 and 563 solid EPDM where the joint suits a solid strip.
Panels near heat exchangers, flue sections, or other warm zones step up to BISCO® HT-870-class cellular silicone (UL 94 listings per the individual grade TDSs), and doors that must latch with light effort take BISCO® BF-1000 Extra Soft. Parts ship to the panel drawing or slit to width for frame-applied strip, through flatbed die-cutting and slitting.
Material guidance. The EPDM family is commonly specified for outdoor HVAC panel duty because its UV and ozone resistance is reported on the grade TDSs and its compression classes match latch-force closures; commodity open-cell foams in the same slot tend to take a set and wick water. Cellular silicone earns its premium where panel temperature or a flame-class callout on the gasket itself drives the choice.
Performance depends on grade, geometry, compression, adhesive system, and environment; final material selection should be validated in the application.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
Panel and door drawings with flange widths and gap ranges (nominal and worst case), latch or screw closure forces if known, lengths and quantities per unit, the weather and temperature exposure of each panel, any flame-class requirement on the material, and whether gaskets mount mechanically or with adhesive backing.
Controls-cabinet gaskets for NEMA/IP-framed enclosures
Somewhere on every packaged unit is the box the rest of the unit exists to feed: the controls and VFD cabinet, where boards, contactors, and drives live a thin steel wall away from rain and washdown spray. Enclosure designs here are commonly evaluated to NEMA 250 types and IEC 60529 IP codes, and the honest version of that sentence matters: the rating belongs to the tested enclosure, not to its gasket.
What the gasket contributes is a compression-class match to the door's real closure force, continuous contact through the corners, and a chemistry that holds those properties through years of heat and weather.
What H-O converts. Die-cut one-piece door gaskets, picture-frame gaskets with molded-corner-free radii, and gland-cover and conduit-plate gaskets from PORON® 4701-series microcellular urethane (methods per ASTM D3574 on the TDS; low compression set keeps a thin gasket sealing through years of door cycles), with PORON® 4701-40V0 where the location demands a UL 94 V-0 class on the gasket itself.
Larger doors and wetter exposures take RE-series EPDM foam or EPDM sponge; warm cabinets and flame-class callouts take BISCO® cellular silicone (the HT closed-cell series, plus the RS-series sponge with UL 94 listings per the individual grade TDSs). The deep enclosure-sealing playbook lives on our switchgear & cabinet sealing page; this job is its rooftop edition.
On adhesive backing. Most cabinet gaskets mount with a pressure-sensitive adhesive, and most HVAC cabinet steel is powder-coated, a lower-surface-energy finish than bare metal. Adhesive-backed gasket performance depends on the substrate, its surface energy and preparation, temperature, exposure, dwell time, applied pressure, joint geometry, and assembly method; the adhesive system should be validated on the actual painted panel before the part is released. H-O laminates the PSA grade your validation selects and documents it per the adhesive vendor's TDS.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
Door and flange drawings (or the enclosure maker and model), the target enclosure type or IP code the design is being evaluated to, compressed-gap range and closure forces, per-unit quantities, the PSA requirement if any, and any flame-class callout. A sample door is the fastest path to a validated PSA recommendation.
Roof-curb seals
Between the rooftop unit's base rail and the roof curb sits the largest gasket on the whole machine, and the only one compressed by the unit itself rather than by a latch. The curb seal carries the dead load of the unit perimeter, follows a curb that is rarely flat to better than a few millimeters, and closes the joint where supply and return air pass through the roof, so a leak here is simultaneously an energy leak, a rain path into the building, and a structure-borne noise path into the deck.
It is specified by compressed thickness under known load, which makes it a materials problem before it is an installation problem.
What H-O converts. Wide slit strips, rolls, and corner and cross-rail pieces from SBE41VN/SBE42VN vinyl nitrile foam and the ENSOLITE® IG1 family (vinyl nitrile, compression classes per ASTM D1056 on the grade TDSs), SCE42B neoprene foam, and RE-series EPDM foam for the weather-exposed perimeter edge. Thick sections cut clean on waterjet; strip stock comes off slitting in installer-friendly lengths.
Material guidance. Closed-cell construction is the controlling property: the seal must not wick water along its own length, and it must sit in a compression range where the unit's dead load flattens it into the curb's irregularities without bottoming it out. Vinyl nitrile and neoprene foams are commonly specified here for their balance of compression class, water resistance, and cost at curb widths; EPDM takes the sun-struck edge.
Size by bearing stress, not by feel: perimeter weight over seal area, checked against the grade's compression-deflection data per ASTM D1056.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
Curb dimensions and rail widths, unit perimeter weight (or model), seal thickness and target compressed height, the curb material and flatness condition if known, lengths per unit, and whether strips ship plain or adhesive-backed for positioning during the set.
Duct-flange & plenum gaskets
Every joint in the supply path is a calibrated leak until it is gasketed: TDC/TDF and slip-and-drive flange connections, plenum access doors, fan-deck penetrations, and the flexible-connector flanges at the unit. Duct construction and allowable leakage are commonly framed by SMACNA duct-construction practice at the system level, with the leakage class belonging to the tested duct system; the converter's contribution is the compressible layer at each flange, cut to the bolt pattern, that lets ordinary screw spacing produce continuous contact.
What H-O converts. Slit gasket tape in flange widths, kiss-cut flange gaskets with bolt-hole patterns, and plenum-door perimeter gaskets from SCE42B neoprene foam (neoprene sponge family) and EPDM sponge, both with compression classes per ASTM D1056 on the grade TDSs. Joints near heat exchangers or in high-temperature plenums step up to BISCO® cellular silicone grades whose TDSs carry the temperature range the joint actually sees.
Adhesive-backed tape strips carry the same validation framing as every PSA part on this page: performance depends on the substrate, surface energy and preparation, temperature, exposure, dwell, pressure, joint geometry, and assembly method, and should be validated on the actual galvanized or painted flange.
Material guidance. Flange gaskets run at low closure forces between thin metal edges, so the soft end of the D1056 class range usually wins: the gasket has to flow into screw-spacing waviness, not fight it. Specify by compressed thickness at the real screw spacing, name the air temperature at the joint, and keep the material's service range (per its TDS) above the design supply temperature with margin for furnace-side sections.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
Flange profile and width, screw or bolt spacing, joint air temperature, target compressed thickness, lengths or gasket counts per unit, and whether parts ship as slit tape rolls, frames, or kiss-cut sets on liner.
Pressure-equalization vents & membranes
A tightly gasketed controls cabinet on a roof breathes whether the designer planned for it or not. Every sun-up and shutdown swings the internal air temperature tens of degrees, the trapped volume expands and contracts, and the pressure difference pulls air, and the moisture in it, past the gaskets at whatever point yields first. The fix is to give the cabinet a designed breathing path: a pressure-equalization vent whose membrane passes air but resists liquid water and dust, so the gaskets can do their job without being asked to fight physics.
Membrane airflow and ingress-resistance values are specified per the membrane vendor's TDS, and the enclosure's rating still belongs to the tested enclosure with the vent installed.
What H-O converts. Die-cut adhesive-backed membrane patches from venting-membrane stock specified per the membrane vendor's TDS, vent-port and snap-in vent housing gaskets from PORON® and EPDM sponge, protective reticulated polyurethane filter foam inserts behind louvers and hoods, and the kiss-cut multi-layer vent assemblies (membrane, carrier, gasket) that ship as one part.
Membrane lamination and multi-layer construction run through laminating and CNC knife cutting. The deep selection logic, airflow versus ingress protection versus area, lives on our filtration & venting application page.
Material guidance. Size the vent area to the cabinet volume and the temperature swing, not to the hole that happens to be free; an undersized vent just slows the pumping without stopping it. For adhesive-mounted membrane patches the PSA ring is the part of the part that fails first when unvalidated: performance depends on the substrate, its surface energy and preparation, temperature, exposure, dwell time, applied pressure, geometry, and assembly method, so validate the patch on the actual cabinet finish.
Membrane family and grade are chosen from the vendor's TDS tables for airflow and water-entry pressure; H-O converts the selected stock and documents it per that TDS.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
Cabinet internal volume and the expected temperature swing, the mounting style (adhesive patch, port gasket, housed vent), hole sizes, the exposure (rain, washdown, dust), per-unit counts, and the enclosure type or IP code the assembled design will be evaluated to.
Filter-rack seals
Air follows the path of least resistance, and in a filter rack that path is rarely through the media: it is the gap between filter frame and track, the unsealed rack-to-casing joint, and the access door that loads the filters. Bypass air carries unfiltered dust straight to the coil, where it becomes a heat-transfer penalty and a cleaning bill; the filters' rated efficiency is only delivered when the rack seals force the air through them.
The parts are small and cheap, the consequence is the unit's whole filtration budget, which is what makes this the classic afterthought worth drawing properly.
What H-O converts. Filter-track and rack-face gasket strips from EPDM sponge and neoprene sponge, access-door perimeter gaskets matched to job 1's door materials, wipe seals of F-1 and F-10 SAE pressed wool felt where filters slide past the seal on every change, and reticulated polyurethane filter foam cut as washable pre-filter pads and louver inserts (PPI grade per the foam vendor's data; methods per ASTM D3574). Per-unit gasket-and-seal kits ship through kitting with parts on liner in assembly order.
Material guidance. Match the seal to the motion: static rack joints take compression gaskets specified by D1056 class, while sliding filter edges take felt wipe seals that tolerate repeated insertion without tearing. Reticulated foam pre-filters are specified by PPI (pores per inch), trading capture against pressure drop; the right grade depends on the dust the site actually produces, and coarse-then-fine stacking is common. Final selection should be validated in the application against airflow and service-interval targets.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
Rack and track cross-sections, filter sizes and counts, the change-out frequency, target gasket thicknesses, airflow per opening for any foam pre-filter (with allowable pressure drop), and per-unit kit quantities.
Where the six jobs live on a packaged rooftop unit
Representative line drawing, not a product photo: a packaged rooftop unit in side view with the six sealing jobs located. Amber layers mark the converted gasket, seal, and vent parts this page covers.
Skip ahead and request your engineering review now
If your drawing set already calls out an EPDM grade, a silicone sponge, a PORON® gasket, a curb-seal cross-section, or a vent-membrane construction, send it over for engineering review against the vendor TDSs and the standards language.
The decisions that drive an HVAC cabinet-sealing spec
A cabinet seal is chosen by the point it closes and what it keeps out — weather, air, or light — then by the force available to close it.
Name the sealing point and the duty first, then match the material to the closure force and the temperature. Gasket grades carry their own compression and flame class per TDS.
Show all 5 selection factors tap to expand
Specification Tools
Two tools to take you from "we're sealing a packaged unit" to here's the converted-parts checklist for the drawing set: a sealing-point checklist builder that assembles the part list with its citations, and a side-by-side comparison of every sealing family on this page.
1. Packaged-unit sealing-point checklist builder
Check the sealing points your unit carries. The builder assembles the corresponding converted parts into a checklist with the family, what to send with the drawing, and the citation language (material classes per vendor TDS; enclosure and duct frameworks by designation). The default selection below is pre-built for a typical packaged rooftop unit; every part is also printed in the material reference section, so nothing here exists only behind a script.
Sealing-part checklist: 3 parts selected
Each checked sealing point adds its part below. The list is the starting bill of materials for the engineering review, not a certification: material classes (UL 94) come from the grade TDS, and enclosure and duct frameworks (NEMA 250, IEC 60529, SMACNA) are cited by designation, with the rating belonging to the tested enclosure or system.
- Door & panel gaskets: RE-series EPDM foam (BISCO® silicone for hot or flame-class duty)Send: flange widths, gap ranges, latch forces, weather exposure per panel. Cite: ASTM D1056 classes per the grade TDS.
- Cabinet gaskets: PORON® 4701 series (4701-40V0 for V-0 duty)Send: door drawings, compressed-gap range, target enclosure type / IP code, PSA requirement. Cite: ASTM D3574 methods; UL 94 V-0 per the 40V0 TDS; rating with the tested enclosure.
- Vent parts: membrane patch per vendor TDS + vent-port gasket + foam louver insertSend: cabinet volume, temperature swing, hole sizes, exposure. Cite: membrane airflow and water-entry values per the membrane vendor's TDS.
2. Side-by-side: HVAC sealing family comparison matrix
Every family called out on this page, with construction, the property that drives its selection, the standards its TDS cites, and the sealing point it serves. Click a column header to sort. Click any material name to jump to its accordion entry.
| Material | Construction | Selection driver | Standards on the TDS / by designation | Sealing point | |
|---|---|---|---|---|---|
| The weather side (doors, panels, curb) | |||||
| RE-Series EPDM Foam + 553/563 Solid EPDMClosed-cell EPDM / solid strip | Closed-cell EPDM foam | UV/ozone duty at latch forces | ASTM D1056 classes per grade TDS | Doors, panels, curb edge | |
| BISCO® Cellular Silicone (HT-870, BF-1000, RS-series)Silicone foam/sponge | Cellular silicone | Temperature endurance / flame class | UL 94 listings per grade TDS; ASTM E84 where reported | Hot sections, rated joints | |
| Vinyl Nitrile Foam (SBE41VN/42VN, ENSOLITE® IG1)Closed-cell VN foam | Closed-cell vinyl nitrile | Bearing stress at curb widths | ASTM D1056 classes per grade TDS | Roof curb | |
| Neoprene Foam (SCE42B class)Closed-cell neoprene | Closed-cell neoprene foam | Low-closure-force flange duty | ASTM D1056 classes per grade TDS | Duct flanges, plenums, curb | |
| The cabinet side (controls, vents, filters) | |||||
| PORON® 4701 Series (4701-40V0 for V-0 duty)Microcellular urethane | Microcellular PU foam | Compression-set resistance, thin gaskets | ASTM D3574; UL 94 V-0 (40V0 TDS) | Controls cabinet | |
| EPDM SpongeSponge rubber | EPDM sponge | Economical weather-side sealing | ASTM D1056 classes per grade TDS | Panels, racks, flanges | |
| Reticulated PU Filter Foam (by PPI) + Vent Membranes (per vendor TDS)Open-cell filtration / membrane | Reticulated PU / membrane laminate | Airflow vs capture / water-entry pressure | ASTM D3574 methods; membrane values per vendor TDS | Vents, louvers, pre-filters | |
| Pressed Wool Felt (F-1 / F-10 SAE)SAE pressed felt | Compressed wool felt | Sliding wipe-seal duty | SAE felt designations per TDS | Filter tracks, wipe seals | |
HVAC sealing failures you can prevent at spec
Packaged-unit sealing fails quietly first: a door gasket that crumbles in its third summer, a cabinet that mists up every morning, a curb joint that whistles, a coil that fouls behind expensive filters. Five patterns cover most of what goes wrong on this page, and each is a specification decision made before the first part is cut.
On outdoor equipment, the paperwork is part of the part. A correct material with an undocumented class, or a drawing note that claims a NEMA type or IP code for a gasket, costs more schedule at review than any cutting error. Cite material classes per the grade TDS; cite enclosure ratings by designation, with the rating belonging to the tested enclosure.
Show all 5 failure modes tap to expand
1. The door gasket that was picked indoors and died outdoors
A commodity foam sealed beautifully at the factory and crumbled on the roof: UV, ozone, and daily temperature cycling are the actual duty for an RTU panel gasket, and they are exactly the properties a price-picked foam was not screened for. The visible symptom arrives in year two or three as chalking, cracking, and a panel that rattles. The fix: stay in chemistries whose grade TDSs report weathering behavior, the EPDM family is the common default for sun-struck panels, and reserve the economical general-purpose foams for interior joints.
Compression class still has to match the latch force per ASTM D1056. [4]
2. The cabinet that lost its rating at the gasket corners
An enclosure design aimed at a NEMA type or IP code passed everything except the water test, and the leak path was the gasket's own corners: four mitered strips with butt joints where one frame should have been, or a compression class so firm the door never closed the gap at the hinge side.
The fix: die-cut the gasket as one part where the geometry allows, match the D1056 class to the real closure force around the whole perimeter (doors close hardest at the latch and softest at the corners), and write the standards language correctly: the design is evaluated to NEMA 250 / IEC 60529, and the rating belongs to the tested enclosure.
3. The curb seal that bottomed out (or never compressed at all)
Two versions of one sizing miss. A seal too thin or too firm for the curb's flatness leaves daylight at the low spots: air leakage, rain entry, and a whistle the building reports before the energy bill does.
A seal too soft for the unit's perimeter weight squeezes flat and transmits structure-borne vibration into the deck. The fix: treat the curb seal as a bearing-stress calculation: perimeter weight over seal area, checked against the grade's compression-deflection data per ASTM D1056, with thickness chosen so the working compression brackets the curb's real flatness error. [4]
4. The sealed cabinet that drank water anyway
The gaskets were fine; the physics was not. A tightly sealed controls cabinet on a roof breathes with every heating and cooling cycle, and without a designed vent the pressure swing pulls humid air past the gaskets at the weakest point, condensing on the coldest board inside.
The morning mist on the HMI window is the diagnostic. The fix: give the cabinet a pressure-equalization vent sized to its volume and temperature swing, with a venting membrane specified per the membrane vendor's TDS for airflow and water-entry pressure, and validate the adhesive ring on the actual cabinet finish.
The gaskets go back to doing their one job. [2]
5. Filter bypass: clean filters, dirty coil
The filters were rated, installed, and changed on schedule, and the coil fouled anyway, because a few millimeters of unsealed track let air around the media instead of through it. Bypass is invisible at install and expensive at the coil, where the fouling becomes a heat-transfer penalty and a cleaning bill. The fix: draw the rack seals as parts: compression gaskets on the static rack joints (D1056 class to the real closure force), felt wipe seals where filters slide on every change, and a gasketed access door.
The whole set typically costs less than one coil cleaning. [5]
Material reference
Detailed specs for the seven sealing families referenced on this page: the weather side (RE-series EPDM foam with the 553/563 solid grades, BISCO® cellular silicone, vinyl nitrile and ENSOLITE® foams, neoprene foam), the cabinet side (PORON® microcellular urethane, EPDM sponge), and the venting and filtration set (reticulated filter foam with vent membranes per vendor TDS, and pressed wool felt).
Values are per the vendor TDS on file for each grade with the method named; enclosure and duct frameworks are cited by designation only, with the rating belonging to the tested assembly.
H-O die-cuts, kiss-cuts, slits, laminates, and kits every family to drawing.
RE-Series EPDM Foam (RE41E/RE42E) + 553/563 Solid EPDMDoor, panel & weather-side gaskets · ASTM D1056 classes per grade TDS
Specify the compression class against the real latch force, not the catalog default; a too-firm grade holds the door open and a too-soft grade takes a set. Adhesive-backed versions carry the PSA validation framing in job 2.
BISCO® Cellular Silicone (HT-870 Soft, HT-800 Medium, BF-1000 Extra Soft, RS-Series Sponge)Hot-section & flame-class gaskets · UL 94 listings per grade TDS
Cite the flame class from the specific grade's TDS, not from the family name; classes belong to listed grades. The RS-series sponge carries its UL 94 listings per the individual grade TDSs.
PORON® Industrial Microcellular Urethane (4701 Series, 4701-40V0)Controls-cabinet gaskets · ASTM D3574 methods · V-0 class on the 40V0 TDS
Specify by compression-force-deflection against the door's real closure force; the family's compression-set resistance is what keeps a thin gasket sealing years in. The rating language stays honest: the gasket supports the design; the rating belongs to the tested enclosure.
Vinyl Nitrile Foam (SBE41VN / SBE42VN, ENSOLITE® IG1 Family)Roof-curb seals · ASTM D1056 classes per grade TDS
Size by bearing stress: perimeter weight over seal area, checked against the grade's compression-deflection data, with thickness chosen so the working range brackets the curb's flatness error.
Neoprene Foam (SCE42B Class)Duct-flange & plenum gaskets · ASTM D1056 classes per grade TDS
Keep the material's TDS service range above the joint's design air temperature with margin for furnace-side sections; silicone takes over where neoprene's range runs out.
EPDM SpongeEconomical weather-side sealing · ASTM D1056 classes per grade TDS
Pick the class to the closure force as with every D1056 material; the sponge classes step soft to firm, and the soft end usually wins at sheet-metal screw spacing.
Reticulated PU Filter Foam (by PPI) + Vent Membranes (per Vendor TDS) + Pressed Wool Felt (F-1/F-10)Vents, louvers, pre-filters & wipe seals · ASTM D3574 methods; membrane values per vendor TDS
For adhesive-mounted membrane patches, the PSA ring carries the standard validation framing: performance depends on substrate, surface energy and preparation, temperature, exposure, dwell, pressure, geometry, and assembly method; validate on the actual cabinet finish.
HVAC sealing & venting materials: engineer-grade FAQ
Ten of the questions we hear most from RTU, AHU, and controls-cabinet teams. If your question isn't here, send a drawing or call, engineering picks up.
Are H-O gaskets NEMA 4 or IP66 rated?
No gasket is, and no honest supplier will claim otherwise: NEMA 250 types and IEC 60529 IP codes evaluate the complete enclosure as tested, so the rating belongs to the tested enclosure, not to any component. What the gasket contributes is documented properties: a compression class per ASTM D1056 or methods per ASTM D3574 on the grade TDS, flame classes like UL 94 V-0 where the grade lists them, and lot-code traceability.
The materials on this page support enclosure designs commonly evaluated to those ratings; the enclosure designer owns the evaluation. [1]
What gasket material works on rooftop-unit doors exposed to sun and weather?
The EPDM family is the common default: UV, ozone, and weathering behavior are reported on the grade TDSs, and the RE-series foam grades carry compression classes per ASTM D1056 that match latch-force closures. Solid 553/563 EPDM suits joints built for a solid strip. Step up to BISCO cellular silicone where the panel runs warm or the drawing names a flame class on the gasket. Final material selection should be validated in the application. [4]
EPDM or silicone for an HVAC cabinet gasket: how do I choose?
By temperature and by flame class. EPDM foam and sponge are the economical weather-side default for most door and panel joints. Move to BISCO cellular silicone when the joint's service temperature per the EPDM grade's TDS runs out (furnace sections, flue-adjacent panels) or when the design brief names a UL 94 class on the gasket itself, with listings per the individual silicone grade TDSs. Match the compression class to the real closure force either way; chemistry choice does not excuse a class mismatch.
How do I size a roof-curb seal?
As a bearing-stress calculation. Take the unit's perimeter weight over the seal's contact area, and check that stress against the grade's compression-deflection data per ASTM D1056 so the seal works in its design compression range, neither bottomed out nor barely touched. Then choose thickness so the working compression brackets the curb's real flatness error. Closed-cell vinyl nitrile and neoprene foams are commonly specified at curb widths; EPDM takes the sun-struck perimeter edge. [4]
What goes on a duct flange, and how does SMACNA fit in?
A soft closed-cell gasket, commonly neoprene foam or EPDM sponge slit to flange width or kiss-cut to the bolt pattern, in the soft end of the ASTM D1056 class range so it flows into the waviness between screws. SMACNA duct-construction practice frames the joint types and leakage expectations at the system level and is cited by designation only: the leakage class belongs to the tested duct system, and the gasket is the converted layer that helps the joint meet it. [3]
Why does a sealed outdoor cabinet need a pressure-equalization vent?
Because temperature swings turn a sealed cabinet into a pump. As the trapped air heats and cools, the pressure difference across the walls pulls outside air, and its moisture, past the gaskets at the weakest point, and the moisture condenses on the coldest surface inside. A vent with a venting membrane equalizes pressure through a designed path that resists liquid water and dust, so the gaskets only have to seal, not breathe. The cabinet's rating still belongs to the tested enclosure with the vent installed. [2]
How is a vent membrane specified?
From the membrane vendor's TDS tables: airflow per unit area against the cabinet's volume and temperature swing, water-entry pressure against the exposure (rain versus washdown), and the mounting format (adhesive patch, port gasket, or housed vent). H-O converts the selected membrane stock into patches and multi-layer vent assemblies and documents the values per that TDS; we do not publish blanket airflow or ingress claims of our own. The deep selection logic lives on the filtration & venting application page.
Will adhesive-backed gaskets stick to powder-coated panels?
Often, with the right PSA, but it has to be validated rather than assumed: powder coat is a lower-surface-energy finish than bare metal, and adhesive-backed gasket performance depends on the substrate, its surface energy and preparation, temperature, exposure, dwell time, applied pressure, joint geometry, and assembly method.
Validate the adhesive system on the actual painted panel before the part is released; H-O laminates the PSA grade your validation selects and documents it per the adhesive vendor's TDS. A sample panel is the fastest path to a recommendation.
What seals a filter rack, and why does PPI matter?
Three parts: compression gaskets of EPDM or neoprene sponge on the static rack joints, pressed wool felt wipe seals where filters slide on every change, and a gasketed access door. Reticulated foam pre-filters ahead of the media are specified by PPI (pores per inch): coarser grades pass more air with less capture, finer grades the reverse, so the grade follows the site's dust and the allowable pressure drop, per the foam vendor's data. Sealing the rack is what lets the filters deliver their rated efficiency. [5]
Can H-O kit the whole per-unit gasket set, and does H-O mold or extrude?
Yes to kitting: door gaskets, cabinet gaskets, curb strips, flange tape, vent parts, and filter-rack seals can ship as one kit per unit, parts on liner in assembly order, with lot-code TDS records per material. H-O and converts sheet, roll, and strip stock to drawing; we do not mold or extrude in-house, and molded or extruded profiles are coordinated through a partner network. Conversion runs in Winsted, Connecticut under an ISO 9001:2015 certified quality management system.
Glossary: terms used on this page
Quick reference for the enclosure, duct, and gasket terminology used throughout. Each entry links to the relevant standard or test method where applicable.
NEMA 250 (by designation)
The NEMA enclosure-type standard (Type 1, 3R, 4, 4X and so on) for electrical equipment enclosures, per [1]. It evaluates the complete enclosure as tested; on this page it is cited by designation, and the gasket materials support designs evaluated to it.
IP code / IEC 60529 (by designation)
The international ingress-protection classification (IP54, IP65, IP66 and so on) per IEC 60529 [2]: first digit solids, second digit water. The code attaches to the tested enclosure, not its gasket; materials here are ingredients of designs evaluated to it.
SMACNA duct-construction practice (by designation)
The Sheet Metal and Air Conditioning Contractors' National Association standards for duct construction and air leakage, per [3]. They frame joint types and leakage classes at the duct-system level; the leakage class belongs to the tested system, and the flange gaskets here serve it.
RTU (packaged rooftop unit)
A self-contained heating-and-cooling unit installed on a roof curb, ducting supply and return air through the roof. Its doors, panels, cabinet, curb joint, duct connections, vents, and filter rack are the six sealing jobs of this page.
Roof curb
The raised structural frame on the roof that supports a packaged unit and passes its ductwork through the deck. The curb seal between unit base rail and curb is the largest gasket on the machine, compressed by the unit's own weight and specified by bearing stress.
Plenum
An air-distribution chamber connecting the unit to its ductwork. Plenum access doors and panel joints are gasketed like duct flanges, with material service temperature checked against the air the plenum actually carries.
ASTM D1056 compression class
The classification system for sponge and expanded rubber per ASTM D1056 [4], grouping grades by the pressure needed to compress them 25%. The number that matches a gasket to its real closure force, reported on the EPDM, neoprene, and vinyl nitrile grade TDSs.
Compression set
The permanent deformation a cellular material keeps after sustained compression. The property that decides whether a door gasket still pushes back after years of latched summers; reported per the method named on each grade's TDS.
Closed-cell vs open-cell
Closed-cell foams trap gas in sealed cells and resist water absorption along their length, which is why weather-side gaskets and curb seals are closed-cell. Open-cell (including reticulated) foams pass air, which is why filters and acoustic media are open-cell. The job picks the cell structure before the chemistry.
PPI (pores per inch)
The pore-count designation for reticulated filter foam. Lower PPI passes more air with coarser capture; higher PPI captures finer dust at higher pressure drop. Specified per the foam vendor's data against the site's dust and the allowable pressure drop.
Pressure equalization (cabinet breathing)
The pressure swing a sealed enclosure develops as its internal air heats and cools. Without a designed vent, the swing pumps moist air past the gaskets; a membrane vent equalizes pressure through a path that resists liquid water and dust, per the membrane vendor's TDS values.
Kiss-cut
Die-cutting through the material but not its release liner, so adhesive-backed gaskets peel off a sheet in assembly order. The standard ship format for cabinet-gasket and flange-gasket sets on this page.
PSA (pressure-sensitive adhesive)
The adhesive layer laminated to a gasket for peel-and-stick mounting. Its performance depends on substrate, surface energy and preparation, temperature, exposure, dwell, pressure, geometry, and assembly method, which is why every PSA part on this page carries the validate-on-the-actual-panel framing.
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
Standards, test methods & technical references
The standards, frameworks, and vendor technical data sheets cited throughout this page. Enclosure and duct frameworks are cited by designation: they evaluate enclosures and duct systems, and the rating or leakage class belongs to the tested assembly. Standards editions current as of June 2026; verify against the publishing body before final spec. H-O converts materials tested to the material-level methods on the source vendor's TDS; H-O does not certify systems or independently certify materials.
[1] NEMA 250 (by designation)
Enclosures for Electrical Equipment (1000 Volts Maximum), published by the National Electrical Manufacturers Association: the enclosure-type framework behind controls-cabinet design on outdoor HVAC equipment. Cited by designation only; the type rating belongs to the tested enclosure.
[2] IEC 60529 (by designation)
Degrees of Protection Provided by Enclosures (IP Code), published by the International Electrotechnical Commission. The international ingress-protection classification referenced in cabinet and vent design; cited by designation, with the IP code belonging to the tested enclosure.
[3] SMACNA duct-construction standards (by designation)
HVAC duct-construction and air-leakage standards published by the Sheet Metal and Air Conditioning Contractors' National Association. The framework behind flange joint types and duct-leakage classes; cited by designation as design context, with the leakage class belonging to the tested duct system.
[4] ASTM D1056
Standard Specification for Flexible Cellular Materials — Sponge or Expanded Rubber, published by ASTM International. The classification and method framework behind the EPDM, neoprene, and vinyl nitrile compression classes cited on the grade TDSs.
[5] ASTM D3574
Standard Test Methods for Flexible Cellular Materials — Slab, Bonded, and Molded Urethane Foams, published by ASTM International. The method set behind PORON® and reticulated-filter-foam property data on the vendor TDSs.
[6] UL 94 (classes per grade TDS)
Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances, published by UL. Flammability classes (including V-0) belong to the listed material grades per their vendor TDSs; this page cites them only where the grade's own TDS reports them.
[7] ASTM E84
Standard Test Method for Surface Burning Characteristics of Building Materials, published by ASTM International. Referenced where individual grade TDSs report surface-burning data; cited at the material level only.
Updated . Standards editions current at publication; verify against the publishing body before final spec. H-O converts materials tested to the methods cited; H-O does not certify systems. Lot-specific documentation available on request.
Get an HVAC sealing & venting materials engineering quote
Send a drawing set, panel sample, or unit spec. We typically respond within one business day with a material recommendation, prototype lead time, and TDS verification against your gap ranges, closure forces, weather exposure, and any flame-class callouts.
See also: related H-O application pages
Engineering content for the adjacent sealing sub-applications, the parent sealing application, and the owning industry hub. Each page covers material selection, failure modes, and converter-side process detail for its application family.
Material data & standards. All compression, temperature, and flame-class values on this page are taken from the source vendor's technical data sheets with the method named (ASTM D1056, D3574, E84; UL 94 classes per the listed grade TDSs; vent-membrane airflow and water-entry values per the membrane vendor's TDS).
Enclosure and duct frameworks (NEMA 250, IEC 60529, SMACNA duct-construction practice, AHRI equipment frameworks) are cited by designation only: they evaluate enclosures, duct systems, and equipment, the rating or class belongs to the tested assembly, and the materials on this page support designs evaluated to them.
H-O converts materials; H-O does not design enclosures or duct systems, does not certify systems, and does not independently certify materials against the standards cited. Performance depends on grade, geometry, compression, adhesive system, and environment; final material selection should be validated in the application against the vendor TDS.
Conversion scope. H-O and converts sheet, roll, and strip stock to drawing in Winsted, Connecticut: die-cut and kiss-cut gaskets and vent parts, slit curb and flange strip, waterjet-cut thick sections, laminated membrane assemblies, and kitted per-unit gasket sets, with material traceability and lot-code TDS records. H-O does not mold or extrude in-house; molded or extruded profiles are coordinated through a partner network. Lead-time and MOQ details are in the process strip and the quote form above.