Can You Put an Awning Over a Furnace or Water Heater Vent?

Yes, but only with at least 36 inches between the top of the appliance and the awning, and only where the sides stay open. That is the figure three tankless water heater makers give for outdoor models, where the heater's front panel is the exhaust. Rinnai's installation instructions for its RE series say "36 inches minimum from the top of the water heater to the overhang" and add that "the area under the overhang must be open on 3 sides." Navien's outdoor vent kit for the NPE-2 sets 36 inches below "a gutter, sanitary pipework, eaves or overhang," and Noritz draws 36 inches from the top of its NRC661-OD to the surface above.

The plastic pipes of an indoor furnace or water heater that exit through the wall are a different case. The US code gives no overhang distance for them, and Carrier's own furnace manual tells installers to avoid venting under a deck or large overhang. A 10 ft patio awning is a large overhang. End it beside the vent instead.

Why you read "12 inches" and "36 inches"

Almost every water heater and furnace manual prints the same lettered table, with a line M that says "Clearance under veranda, porch, deck, or balcony: 12 inches," and a footnote that it is "permitted only if veranda, porch, deck, or balcony is fully open on a minimum of two sides beneath the floor." Many readers take that as permission to vent under any roof open on two sides, 12 inches up.

Read the column headings. In Rinnai's Technical Bulletin 26 and Bulletin 108, the 12 inches sits in the Canadian column, under CSA B149.1. The US column for the same line carries an asterisk, and the asterisk means "clearances are in accordance with local installation codes and the requirements of the gas supplier." Navien's concentric vent kit, which lists US installations only, shows that asterisk on line M too. So do the two soffit lines, D (a ventilated soffit within 2 ft horizontally of the vent's centerline) and E (an unventilated soffit). The National Fuel Gas Code, ANSI Z223.1/NFPA 54, simply does not give a number for a roof over a vent.

Where the code is silent, the appliance maker decides, and for outdoor water heaters the makers wrote 36 inches. The 12 inch figure survives because it is the only number on the "porch" line. For a US home it does not govern.

What the manuals say, side by side

Eight documents from four manufacturers and one gas utility, checked October 2026. The first three rows cover outdoor tankless heaters; the rest cover vents from appliances installed indoors.

No document gives a number lower than 36 inches for anything over an outdoor heater, and none gives any number at all for a roof over a US sidewall vent. That gap is why the advice online is so uneven.

Outdoor tankless heaters: measure to the part directly above

An outdoor tankless heater hangs on the wall with its exhaust opening on the front of the cabinet. A retractable awning hangs on the same wall, and its cassette or roller lands right over the heater. So the number that matters is the gap from the top of the heater to the lowest point of the awning directly above it. That is the underside of the cassette, hood or roller and any bracket, not the front bar, which is several feet out.

Many installations pass. The awning mounting height guide puts the brackets of a 10 ft awning at about 9 ft 5 in (113 in) for 84 in of headroom. If the cassette hangs within 12 in of that, its underside is at 101 in or higher, so any heater whose top is at 65 in or lower clears it. The ones that fail are heaters mounted high on the wall and low awnings fitted under a short wall, such as a door awning placed right over the heater.

The open sides matter as much as the height. A retractable awning is open at the front and both ends, so it meets Rinnai's "open on 3 sides" without trying. Drop shades, side screens or a wall on one end change that. With the shades down, the heater sits in a box, which is what Noritz means by "stagnant air" and what its "do not enclose" warning forbids.

Navien and Noritz also want 24 in clear in front of the heater, so a fixed awning post in front of the exhaust fails even when the height is fine.

Sidewall vents from indoor furnaces and water heaters

A high-efficiency furnace, boiler or tankless heater inside the house usually vents through the wall with two plastic pipes or one concentric fitting, often a foot or two above grade and sometimes right next to the patio. Here the US tables leave the overhang line blank. That is not permission. It means the decision moves to the furnace maker and your local code.

Carrier's 59SC6A manual gives the furnace maker's view: "Avoid venting under a deck or large overhang. Recirculation could occur and cause performance or system problems. Ice build-up may occur." Its next notes ask installers to place vents "to avoid ice build-up on and moisture damage to surrounding surfaces," and not near soffit vents "or other areas where condensate or vapor could create a nuisance." For a vent near an inside corner, the one case where the manual gives its own numbers, it asks for 6 ft to a soffit above and does not allow the vent under a veranda, porch or deck at all.

A patio awning over a sidewall vent invites all three. The warm, wet plume rises into the fabric instead of away from the house, some of it can be drawn back into the intake pipe beside the exhaust (the recirculation Carrier warns about), and in winter the moisture freezes on the cassette and fabric. Repeated wetting from below also feeds mildew on awning fabric.

The tables give one usable boundary. Line D treats a soffit as "above the terminal" when it is within 2 ft horizontally of the vent's centerline. So the simplest layout that keeps the awning out of the question is one whose nearest end stops at least 2 ft to the side of the vent, measured from the pipe's center. If the awning has to cover that stretch of wall, the clean fix is to have an HVAC contractor move the vent terminal, or take it up through the roof, under the manufacturer's venting rules. Carrier's manual calls the roof location preferred anyway.

Vents near the patio door the awning covers

An awning nearly always sits over a door, and vents have their own distance from doors that the awning does not change. The direct vent figures in the Hawaii Gas guide, which follows NFPA 54, are 9 in from any opening for appliances up to 50,000 Btu/h and 12 in above that, the same figures Carrier's US table gives. A power vented appliance that is not direct vent, meaning it draws its combustion air from the room, needs 4 ft below or beside a door or window that opens, or 1 ft above it.

A roof overhead and still air make those distances less forgiving, because the plume lingers under the cover instead of rising away. If a vent sits close to the door you want to shade, check its distance first; one that is already too close is a job for your gas installer, not the awning maker.

Other equipment on the same wall

The wall behind a patio tends to collect equipment. If the heater's gas supply comes from a meter on that wall, the utility's own rules for covers over the meter and its regulator vent apply as well; they are in awning over a gas meter. A heat pump or condenser beside the heater has its own top clearance, usually larger (see awning over an AC condenser). A standby generator's exhaust rules are in generator under an awning, and a heater you put under the awning on purpose is covered in patio heater clearance. A gas pool heater or pool heat pump on the equipment pad nearby needs 3 ft to 72 in above it, by model (see pool heater under an awning). Mark every one of these zones on the wall before you take the measurements in how to measure for an awning.

Where this answer stops applying

• Your model's manual. The figures above belong to the documents named. Other models and later editions can ask for more.
• Local code and the gas supplier. Every US table hands the blank lines to them. Some jurisdictions add their own rules. Massachusetts, quoted in Carrier's manual, requires hard-wired carbon monoxide detectors with battery backup when a sidewall vent ends less than 7 ft above finished grade, "including but not limited to decks and porches." If the awning is part of a permitted project, raise the vent at that stage (see awning permits and HOA rules).
• Retracted or extended. No manual allows an awning over the vent just because it is usually rolled up. The cassette stays put, and the appliance runs whenever the awning happens to be out.
• Snow. Rinnai's 12 in above grade applies to the anticipated snow line too, so a low vent has to stay clear of snow that slides off the awning or drifts under it. Retract the awning in snow (see awnings and snow).
• Not gas. Dryer vents, wood and pellet stove chimneys and gas fireplace vents have their own manuals and are not covered here. Neither are oil burners.

Frequently asked questions

How far above an outdoor tankless water heater can an awning be?

At least 36 inches from the top of the heater to the lowest part of the awning above it. Rinnai, Navien and Noritz all use 36 inches, and Rinnai adds that the space under the overhang must be open on 3 sides.

Can a furnace vent be under a porch roof or awning?

The US fuel gas code gives no distance and leaves it to local code and the manufacturer. Carrier tells installers to avoid venting under a deck or large overhang because exhaust recirculates and ice builds up. The 12 inch figure in vent tables is the Canadian rule. Keep the awning at least 2 ft to the side of the vent.

Sources and further reading

• Rinnai: RGBRE Recess Box Installation Instructions, 100000800
• Rinnai: Technical Bulletin 26, Outdoor Terminal Clearances and Technical Bulletin 108, Updated Terminal Clearances for Outdoor Water Heaters (10/2014)
• Navien: Outdoor vent cover kit for NPE-2, installation manual
• Navien: Concentric Vent Kit Installation Instructions
• Noritz America: NRC661-OD Installation Manual (Rev. 04/13)
• Carrier: 59SC6A Installation, Start-up, Operating and Service and Maintenance Instructions, 59SC6A-03SI (edition 7/26)
• Hawaii Gas: Engineering guide: gas vent or chimney termination