Outdoor HVAC Units for Landscapers, Fence and Deck Builders

Why this matters

The outdoor unit of an air conditioner or heat pump is the one piece of the HVAC system that sits in somebody else's work zone. Landscapers mulch around it, fence builders screen it, deck builders build over it. Every one of those jobs can leave the unit choking on its own hot exhaust, sitting in a puddle, or cut off from its power and refrigerant lines, and none of it shows on the day the job closes. It shows in July as high bills, a compressor tripping off in the afternoon, or a dead unit and an HVAC tech asking who built the screen.

Safety first

• The unit can start on its own at any time. The thermostat calls, the fan spins up, and fingers or tools near the fan guard or coil fins get hurt. Before working within arm's reach of it, ask the homeowner to set the thermostat to off, and treat the unit as live anyway: you do not open its panels or its disconnect.
• A cut or damaged power whip (the flexible conduit from the disconnect box to the unit): stay back, keep tools and people away, do not touch it or the unit, and have the homeowner switch off the outdoor unit's breaker at the main panel from a dry floor. Call an electrician and the HVAC company.
• A cut refrigerant line (hissing, oily spray, frost): step back from the spray, which can freeze skin, keep flames away, and call HVAC. Under federal Clean Air Act Section 608 rules (40 CFR Part 82, Subpart F), only certified technicians open or repair the refrigerant circuit.

How the unit breathes

Most residential condensers and heat pumps pull outdoor air in through the coil on their sides and blow it straight up out of the top fan. In cooling mode that discharge air is noticeably hotter than the yard; the unit is dumping the heat it pulled out of the house. A heat pump in heating mode does the reverse: the air leaving the top is colder than the yard, and the coil frosts in cold, damp weather, then defrosts and drains meltwater out of the base.

Anything that makes the unit breathe its own exhaust is called recirculation. Hot discharge air that gets pulled back into the coil makes the refrigerant pressures and the compressor's power draw climb, cooling capacity drop, and on a hot day can trip the unit's high-pressure safety. The common causes in other trades' work:

• A deck or roof built over the unit. The top discharge hits the underside and rolls straight back down into the coil.
• A solid screen or fence close around it. The hot plume has nowhere to go but back in.
• Shrubs, tall grass and ornamental plantings pressed against the coil, and mulch piled up the base.
• A dryer vent aimed at the unit, coating the coil in lint.

The required clearances come from the unit's installation manual, not from a rule of thumb: each make and model states a minimum on each side, a larger one on the service side where the electrical panel is, and a clear height above the fan. Find the model number on the unit's label and get the manual before you design anything around it.

The plan view: what has to stay clear

 PLAN VIEW, HEAT PUMP BESIDE A HOUSE WALL

 ============ HOUSE WALL ===========================
   [DISCONNECT]        |line set + low-volt wire
   |<-30 in->|         |into wall, runs along wall
   | working |         |under the mulch 3 ft right
   | space   |   +-----+-----+     ..........
   | 36 in   |   | 12 in gap |     .        .
   | out from|   +-----------+     .        .
   | wall    |   |  UNIT     |-----whip to disconnect
   |         |   |  30 x 30  |     .        .
             |   | fan above |     .        .
  SCREEN     |   +-----------+     .        .
  RETURN ----+   | service   |     ...SCREEN.
  (open slat)    | side, gate|        RETURN
                 +-- GATE ---+
     SCREEN FRONT, open slat, no lid, no roof

The disconnect. The National Electrical Code wants a disconnecting means within sight from and readily accessible from the AC equipment (NEC 440.14, as adopted by your jurisdiction); "within sight" is defined in NEC Article 100 as visible and not more than 50 feet away. Inspectors commonly also apply the working-space rule of NEC 110.26 to that disconnect, which for a typical 240 volt residential unit means a clear space 36 inches deep in front of it and at least 30 inches wide. A fence panel, a gate post or a planted shrub in that space is a code problem and a practical one: the tech has to stand there to open it.

The pad. The unit sits on a plastic or concrete pad that should stay level and above the surrounding grade. A pad that settles or tips stresses the copper lines and their brazed joints where they connect at the unit, and a heat pump sitting low in a hole of mulch drowns its own defrost water, which then freezes into a block of ice around the base coil in winter. Never shim, lift or move a unit; if the pad is tipping or sinking, report it.

The line set and the whip. The copper line set (two pipes, one wrapped in black foam) and a thin thermostat cable run from the unit to the house, sometimes straight into the wall, sometimes along the foundation under the mulch or in a shallow trench. The power whip runs from the disconnect to the unit. A shallow edging trench, a fence post or a landscape spike driven along the foundation is exactly where they get cut. The 811 locate service marks utility-owned lines; it does not mark these. See related: How to Find the Private Lines a Utility Locate Will Not Mark.

Mulch, plants and grade

• Keep a clear ring. Plantings that will be pressed against the coil at full size do not belong in that ring, which is at least the side clearance the manual calls for. A shrub that is 18 inches tall at planting and 4 feet wide in three years is a recirculation problem you are installing now.
• Keep mulch and soil below the pad. Mulch heaped up the sides wicks water into the base and blocks heat pump drainage, and soil piled against the pad lets it settle unevenly.
• Keep the grade falling away from both the house and the pad. A new bed that holds water at the pad turns the unit's base into a pond.
• No string trimmers on the fins. The coil fins are thin aluminum and fold flat at a touch. Trim by hand inside the ring.

Worked example: a fence screen around a heat pump

A homeowner asks a fence crew to hide the heat pump beside the patio with a solid board screen: a front panel 48 inches out from the house wall and two returns back to the wall, 42 inches apart, 5 feet tall, with a lattice lid "so you can't see it from the deck."

Get the numbers that govern. The crew reads the model off the unit label and finds its installation manual. The unit's footprint is 30 by 30 inches and it sits 12 inches off the house wall. For this example, say the manual calls for 12 inches clear on the coil sides, 24 inches on the service side, and 60 inches clear above the fan. Those are illustrative; the figures for the real unit are the ones the crew reads.

Check the customer's design.

• Depth: the unit's front face sits 12 + 30 = 42 inches from the wall. A screen at 48 inches leaves 48 - 42 = 6 inches on the service side, against 24 required. Short by 18 inches.
• Width: 42 inches of inside width minus the 30 inch unit leaves 12 inches total, or 6 inches each side, against 12 each side. Short by 6 inches per side.
• Height above: any lid fails the 60 inch clear height outright.
• Disconnect: its center is on the wall 40 inches left of the unit, and the customer wants the screen to hide it too, which would wall off the space the tech stands in to open it.

The redesign.

• Inside width: 12 + 30 + 12 = 54 inches. Inside depth: 12 + 30 + 24 = 66 inches from the wall, with a gate in the front panel on the service side so the tech can get in.
• Open slat construction rather than solid boards, so air moves through the sides, and no lid. If the manual states a minimum free area for screens, the slat spacing has to meet it.
• The left return sits 12 inches left of the unit, and the disconnect stays outside the screen: its 30 inch wide working space, centered on the box, runs from 25 to 55 inches left of the unit, clear of the return, and 36 inches deep.

The post layout. The right return's back post is planned at the house wall, 12 inches right of the unit. The crew traces the line set: it leaves the unit, turns right along the foundation under the mulch, and enters the wall about 3 feet to the right, so it passes directly under the planned post. The post shifts 10 inches outward, and the crew hand-digs the last two post holes near the foundation rather than augering them.

Check the result. Service side 66 - 42 = 24 inches, coil sides 12 inches each, nothing above the unit, the disconnect's working space outside the screen, the line set untouched. The screen is 12 inches wider and 18 inches deeper than the customer drew it, and the crew explains why in one sentence: a tight solid box with a lid makes the unit breathe its own hot air, raises the bill and shortens the compressor's life.

Decks, noise and units that are already in the way

A deck over or around the unit. Never build over the top discharge. A deck that wraps around the unit needs the same side and service clearances as a screen, and the unit needs to come out someday: leave a way to get a replacement unit in and the old one out without demolishing boards.

Noise. Moving a unit closer to a neighbor's bedroom window or into a corner that reflects sound can push it past a local noise limit. Units are not moved by fence or deck crews, but a screen design can change how much noise reaches a neighbor. See related: How to Place Outdoor Equipment Inside Noise Limits.

The customer wants the unit moved. Relocating a condenser means recovering refrigerant, cutting and brazing the line set, and rerouting power; it is HVAC and electrical work, usually permitted. Price your job around the unit where it is, and if the customer wants it elsewhere, that is a separate call to the HVAC company before you set posts.

Snow country. Heat pumps in cold climates often sit on a raised stand so the base clears snow and defrost water drains; a fence or bed that drifts snow against it defeats the stand. Leave the drift side open.

The words to use when you call

"I'm the fence contractor at [address], building a screen around the heat pump by the patio. Before I set posts: the line set runs along the foundation to the right of the unit under the mulch, and the pad has settled about an inch on the left corner. I haven't touched either. Can you confirm the clearances for this model and look at the pad?"

References

• National Electrical Code, Article 100 (definition of within sight), Section 110.26 and Section 440.14, as adopted by your jurisdiction.
• U.S. EPA refrigerant management rules under Clean Air Act Section 608, 40 CFR Part 82, Subpart F.
• The outdoor unit manufacturer's installation manual for clearances and screening.
• See related: How to Place Outdoor Equipment Inside Noise Limits
• See related: How to Find the Private Lines a Utility Locate Will Not Mark