Best Ways to Keep Outside Air Conditioning Unit Cool

<i> Dulley is a Cincinnati-based engineering consultant</i>

QUESTION: Our outdoor central air-conditioner compressor unit is located in the hot afternoon sun. Is there any type of cover I can make myself to shade it so it operates more efficiently?

ANSWER: Keeping the outdoor compressor unit and the air surrounding it cooler can make your central air conditioner operate more efficiently. Condenser coils can dissipate more heat when the air around them is cooler.

In addition to better efficiency, the maximum cooling output from your air conditioner is greater when the air around it is cooler. This is particularly important on the hottest summer afternoons, when you need the greatest amount of cooling output to keep your house comfortable.


Shading the entire side of your house and the outdoor air-conditioner unit is most effective. This can be done with trees or an awning. Particularly with a brick, masonry or stucco house, the house wall acts like a huge solar collector and actually raises the temperature of the air around the air conditioner.

You can make a simple cover to shade your air conditioner outdoor unit. Check with your air-conditioning contractor about the proper clearance for air flow. Adequate air flow is essential for high efficiency.

One effective air conditioner cover provides both shade and storage. Depending on how large you make this storage/air conditioner cover, you can store your garden tools, fertilizers, etc. Also, the larger you make it, the more shade it provides.

It is basically a plywood storage compartment built several feet back (check with your contractor) from the condenser unit. Build it with a sloped roof (for shade) that extends up over the condenser unit and attaches to your house. The sloped roof gives added height for adequate clearance and it blends better with the lines of most houses.

Make the frame for the storage unit/cover with any common lumber. Cover the storage compartment with plywood siding. Install a piano hinge on the top so you can open it.

Nail the plywood siding over the rest of the sloped top to cover the condenser unit. Leave the sides by the condenser uncovered to allow for adequate air flow.

You can write to me at the address below for Utility Bills Update No. 161 showing a diagram and do-it-yourself instructions for making a storage unit/air-conditioner cover. Please include $1 and a self-addressed stamped business-size envelope.

Rectangular Ducts Less Efficient Than Round

Q: I am building a new house and am at the point of installing the heating and air-conditioning duct work. Is it better to use round or rectangular duct work?

A: From strictly an energy efficiency standpoint, a round duct is more efficient than a rectangular one. The air flow is freer and there is less duct surface area for a given duct cross-sectional area. This means less warmth or “coolth” is lost through the duct-work surface before the conditioned air gets to your rooms.

Rectangular duct work is more convenient to run between wall studs. Both types of duct are often used in the same system. Round ducts can be run from the air handler to rectangular ducts in the walls. No matter which type of duct is used, be sure to seal carefully all the joints with duct tape. Also, insulate any ducts that run through an unconditioned space.

Protect Your Air Conditioner

Your air conditioner unit will operate more efficiently if it is shaded from the sun. This do-it-yourself air conditioner cover also provides storage for lawn and patio needs. Adequate clearance House wall Air conditioner Storage compartment Hinge Plywood siding