Heat waves and air conditioners

If you’re living under the heat envelope covering much of the country this week and your air conditioner seems to be losing the battle of the thermostat, don’t worry. It’s not broken. It’s just been given more to do than it can handle.

Home air conditioning systems were never designed to sustain an inside temperature in the mid-70s while the outside temperature hovers around 100 or more.

Central air-conditioning systems are quirky devices. They must be sized “just-right” in order to cool your house while also dehumidifying it so the cool air doesn’t make you feel clammy.

If you have ever been the first lunch customer in a large and busy restaurant on a hot summer day, you may have experienced the effects of an air-conditioning system that is too large for the heat load at hand.

You walk in the door and immediately feel cold and clammy. That’s because the 15-ton unit on the restaurant’s roof can quickly drop the temperature but it doesn’t remove the humidity in the air.

Once the restaurant has seated 150 people and the gas burners in the kitchen are going full blast, there will be enough heat (or, as we home inspectors say, “heat load”) to drive out the humidity and let the cooling system keep everyone comfortable.

In doing home inspections on really hot summer days, I usually warn my clients that the house we are inspecting will get warmer inside as our inspection progresses, but they shouldn’t worry that the air conditioning system is undersized or malfunctioning.

It simply means that if the system were large enough to combat a heat wave, it would leave the house feeling cold and clammy on normal summer days – and the moisture would also encourage mold to grow.

Like many things in life, air conditioning systems involve trade-offs. Heat waves outside means that the inside temperatures may be warmer than you’d like. But the alternative is an industrial-sized system that will leave you feeling cool and clammy – and might even give you some ugly mold.

So if your air conditioning system seems to be struggling under this heat wave, rest assured that everyone else’s is too.

–Jack Reilly