How Much Clearance Does an Awning Need Over an AC Condenser?

An awning over an air conditioner condenser or heat pump should sit at least 5 feet (60 inches) above the top of the unit and be open on all sides, unless your unit's manual allows less. Five feet satisfies every manual checked here: Goodman permits 36 inches under an overhang only if something deflects the warm discharge air out from under it, Allied (a Lennox company) and Carrier ask for 48 inches above the unit, and an Oxbox heat pump manual from Trane Technologies asks for 60 inches. The awning's real job is keeping ice, snow and roof runoff off the unit; the shade is worth very little, and blocking the discharge costs far more.

Top, side and service clearances from the manuals

All four units below pull air in through the coil on the sides and blow it straight up, so an awning sits directly in the discharge plume.

A standby generator beside the condenser follows the same pattern with a stricter number: Generac wants any overhang 5 ft above the top of the generator and over its service space, and says not to aim generator discharge into an AC condenser. The figures are in can you put a generator under an awning.

The top figures run from 36 to 60 inches, but Goodman's 36 is conditional. Its first instruction is that the top "should be completely unobstructed," and the 36 inches applies only with a way to push discharge air out from under the overhang. A flat awning roof does the opposite and holds the plume over the coil.

Allied's 36 inch footnote is a different limit, a cap on how far a soffit may project over the unit. An awning covering the whole unit exceeds it by design, one more reason for extra height.

Two feet or six feet? Where the confusion comes from

The figures online run from 2 to 6 feet, and both ends come from one page: the U.S. Department of Energy's Building America Solution Center guide, run by Pacific Northwest National Laboratory. It says recommendations "vary considerably" and "6 feet is a commonly recommended distance," then later tells you to check the manual for the height: "at least two feet."

The manuals settle it. Two feet is below every top clearance in the table, including Goodman's conditional 36 inches. Six feet is more than any of them demands, and nothing in them says it is too much. Build to two feet and you are under your manufacturer's minimum.

The Florida Solar Energy Center (FSEC) gives a reason to lean high. In smoke flow tests it found that "even small obstructions in the exhaust jet may easily induce eddy currents in the flow vortex which result in recirculation of air from the exhaust to condenser inlet." Its conclusion: units "should be located several feet away from overhangs, vegetation or other obstructions," and the minimum clearances manufacturers print "may be based more on practicality than for providing optimal performance." The manual figure is a floor; more height is better.

What shading a condenser actually saves

FSEC tested the familiar advice in 1993 and 1994 on three occupied homes in Merritt Island, Florida, each with an unshaded, west-facing outdoor unit, measuring air temperature one foot from the condenser inlet and cooling electricity before and after shading.

Site 2 is the case closest to an awning: a simple overhead structure "as commonly advocated by consumer publications." It barely changed the inlet air. The authors suggest its small saving "may be attributable to reduced direct solar gain to the air handler section of the packaged unit," a section a split system keeps indoors.

Site 3 is the warning. The trees were placed with "particular care" to keep airflow free, yet cooling consumption rose by over 15%; the authors speculate discharge air mixed back into the intake.

Shade does so little because a typical 3-ton unit moves about 2,800 cubic feet of air a minute, far more than the shaded pocket beside it. FSEC calculated that devices which only shade the unit itself "cannot be expected to lower the average AC inlet temperature by more than 0.2 F," and put the efficiency gain at "approximately 1.2% per F" of cooler inlet air. Across all three homes the measured average saving was 0.1%, plus or minus 2.0%.

FSEC's own conclusion: "any savings produced by localized AC condenser shading are quite modest (<3%) and that the risk of interrupting air flow to the condenser may outweigh shading considerations." To cut cooling energy, shade the glass instead: awning energy savings shows what an awning over west or south windows removes.

So why put an awning over it at all?

For protection. The DOE page opens by saying awnings "protect the outdoor compressor unit of your heat pump or air conditioner from snow, rain, and hail." Its photo shows a heat pump encased in ice from roof water dripping on it in winter. Three of the four manuals also say roof water, snow and ice must not fall directly on the unit. Under a roof edge with no gutter, a small roof over the unit fixes a real problem.

Heat pumps need this more, because they run all winter. The Oxbox manual has them raised 3 to 12 inches in snow country so defrost meltwater drains before it refreezes, plus a drift barrier where snow piles up; an awning does nothing about drifts at the sides. See awnings and snow for the load a cover must carry and awnings and hail for which roofing materials survive it.

Designing the awning: height, depth, sides and roof

1. Height. Measure from the top of the fan guard to the lowest point of the awning, not the brackets. Aim for 60 inches or more, and never go below your model's figure.
2. Sides. Leave every side open. The DOE page says "do not include sides on the awning unless they are ventilated," and shows a kit with side panels as "not a recommended design." Posts must keep the side clearances in the table (12 inches at most).
3. Depth and width. The DOE page asks for a roof "slightly larger than the compressor," extending "beyond the HVAC unit on all sides." Allied warns against roof lines "which would allow water or ice to drop on, or in front of, coil or into unit," so carry the drip line past the unit or add a gutter.
4. Roof pitch. For snow, the DOE page gives 6/12 to 12/12 so it slides off.
5. Service access. Keep the service side clear for 18 to 30 inches, depending on the manual, and keep the awning high enough that a technician can lift off the top panel and fan.
6. Attachment. The DOE page says to anchor into studs, add L-flashing, and leave about an inch between the siding and the awning top. Mounting an awning on vinyl siding covers the brackets.

For the cover itself, a small fixed awning in metal or polycarbonate is the usual choice. The DOE page says these do not typically need a permit but to check with your building department and HOA; awning permits and HOA rules explains what they usually ask.

When a patio awning extends over the condenser

More often it is a patio awning that happens to reach over the unit. The same clearances apply, measured at the front bar.

West-facing units and where to put a new one

FSEC's best site cooled the inlet air 3.3 F at the late afternoon peak, with watered trees shading the unit and the ground around it. The study's preferred strategy is location: an outdoor unit "in an unobstructed location on the shaded north side" of the house.

All three FSEC units faced west, and a roof overhead does little against low western sun. As sun angles for awning design shows, a late afternoon sun 37 degrees high slides about 1.3 ft under an overhead edge for every foot of height, so a roof 5 ft above a west-facing unit casts its shadow about 6.5 ft back toward the house at that hour. Unless the awning reaches far out past the unit, the coil sits in full sun when it is hottest. Shade that worked then would have to hang in front of the intake, which the manuals forbid.

Where this answer stops applying

• Front or side discharge units. Every unit in the table blows straight up. A unit that discharges horizontally, like the FSEC site 2 packaged unit, has a different plume, and its own manual governs. Ductless mini splits blow out of the front, so their manuals limit how far a roof reaches past the fan as well as its height: see awning over a mini split outdoor unit.
• Older manuals. The Carrier figure comes from a 1994 manual and the Goodman figure from a 2004 one. Current manuals may differ.
• Multiple units. Two units side by side need 24 inches between them in the Allied, Carrier and Oxbox manuals, and one awning over both has to clear both plumes.

Frequently asked questions

How high should an awning be above an AC unit?

At least 5 ft (60 in) above the top of the unit, measured to the lowest point of the awning, with all sides open. That meets every manual checked here: Goodman's 36 in (which needs a discharge deflector), Allied's and Carrier's 48 in, and Oxbox's 60 in. If your own manual gives a larger figure, use it.

Does shading an AC condenser save energy?

Very little. The Florida Solar Energy Center measured three homes and concluded savings are "quite modest (<3%)." A shade over the unit cannot lower the average inlet air by more than about 0.2 F, worth about 0.25% in efficiency, while one badly placed planting raised cooling use by over 15%.

Sources and further reading

• U.S. Department of Energy, Building America Solution Center (PNNL): Install an Awning Over an Outdoor HVAC Condenser Unit
• Goodman Manufacturing: Installation and operating instructions for split system condensing units, IO-101H (10/04)
• Allied Air Enterprises (Lennox International): 4SCU16LS series installation instructions, 507607-03
• Carrier: 38TRA installation and start-up instructions, form 38TRA-3SI
• Oxbox (Trane Technologies): J4HP4 14 SEER split system air conditioner and heat pump installation instructions
• Parker, D. S., Barkaszi, S. F. and Sonne, J. K., Florida Solar Energy Center: Measured Impacts of Air Conditioner Condenser Shading, FSEC-PF-302-96 (1996; catalog record)