Outdoor Unit Under a Deck With a Decorative Louvered Enclosure
A 3-ton cold-climate heat pump is being installed on the rear wall of a duplex. The chosen spot is under a pressure-treated deck that is 7 ft above grade, with the unit's back 10 in. from the house wall and its left side 12 in. from a privacy fence. The outdoor design temperature is 15°F, and the unit will produce defrost water on a concrete walkway that slopes toward the garage. The installer plans a wall-mount bracket 12 in. above grade, with the service valves facing the walkway. The homeowner has already built a louvered enclosure around the unit to hide it; the louvers are fixed and the enclosure is 18 in. from the unit on three sides. The unit's manual lists 24 in. side clearance, 60 in. top clearance, and 12 in. rear clearance.
1. Evaluate the proposed location for clearances and air recirculation. What would you tell the homeowner?
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The proposed location fails the manual's clearances in at least three ways: rear 10 in. vs 12 in. required, side 12 in. vs 24 in., and top clearance under a 7 ft deck likely less than 60 in. above the unit. The fixed louvered enclosure is only 18 in. from the unit and adds a fourth restriction. Discharge air will short-circuit back into the coil, raising head pressure, reducing capacity, and causing long or repeated defrost cycles.
In heating, the unit also needs to exhaust cold defrost vapor; a confined space keeps moisture and ice around the coil. Relocate the unit to an open wall or pad with the full clearances, or remove the enclosure. If the enclosure must stay, it must be designed with the manufacturer's clearance and free-area requirements, not a decorative louver panel. Do not accept “it fits” as the criterion; the unit must have unrestricted airflow.
2. How should defrost drainage and ice control be handled at this site?
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In heating, defrost water can be several gallons per day. The walkway is a bad discharge point: it will ice and create a slip hazard. Provide a drain pan under the unit with a heat tape or a heated drain kit if the manufacturer allows it, and pipe the condensate to a gravel dry well or grade away from the walkway. Slope the line at least 1/4 in. per foot and protect it from freezing.
Elevate the unit above expected snow depth; 12 in. is a common minimum, but 18 in. or more is better in a 15°F climate with drifting. Do not let the drain line terminate under the unit where it can refreeze. Also check that defrost vapor will not stain or damage the deck above. If the location cannot drain reliably, choose another location.
3. What mounting, service-access, and electrical details must be resolved before installation?
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Mount the unit on a stand or bracket rated for its weight and the local wind/seismic load, attached to framing, not just siding. Use vibration isolators to keep noise out of the duplex, and keep the service valves accessible. The wall bracket should hold the unit level and above snow, with the line set protected from UV and physical damage.
Electrical: the disconnect must be within sight of the unit, and the whip must be protected from abrasion. Leave the service panel accessible and do not block the walkway or egress. If the unit is under a deck, verify that snow shedding from the deck will not bury the unit. Finally, confirm the manufacturer's mounting and snow-stand instructions, because a bracket that voids the warranty is not a saving.