Maybe a better question is, when does a heat pump need help. In this article, I’m going to do my best to explain the when and the why.

Before I do, though, let me make something clear for all you heat pump lovers and installers. I have nothing against heat pumps. In fact, I have installed my fair share of them over the years. I believe that, when installed correctly (doing a load calculation and proper duct design), a heat pump can be a very comfortable and economical system for the customer. And that’s what we always want to provide — comfort with the lowest possible energy cost.

Heat Pump Operation

First, let’s look at the heat pump and how it works. The heat pump is like a conventional air conditioner except that it also provides heat in winter.

In the summer, the heat pump collects heat from inside the house and expels it outside. In the winter, the heat pump extracts heat from outside air and circulates it inside the house. The heat pump works just fine when the outdoor temperature is 40 degrees F or above. Below 40 degrees, supplementary heat is often needed, which usually is in the form of electric resistance heating elements.

When these babies kick in, you can go outside and watch your meter run laps around the house! OK, I’m exaggerating, but this is where it can get very costly. Just prior to the electric resistance coming on, the air that is supposed to be providing heat is actually getting cool.

Are you starting to see the “why”?

Now we’ll talk a little more about the heating cycle of the heat pump. The idea is that during the heating cycle, the heat pump’s outdoor coil is going to absorb heat from the outside air. Let’s think about that. The last time you were outside in 40 degree weather, or even lower temperatures, were you wearing a T-shirt, sweating like a pig, and wishing you had a nice, cold glass of iced tea? I didn’t think so. Would you agree that there is not very much warm air available below 40 degrees? All I’m trying to say is that in areas with climates that typically stay above 50 degrees, a heat pump is a great source of economical comfort. However, I live in northeastern Pennsylvania. In this type of climate, it’s time to incorporate a “heat pump helper.”

Auxiliary Heat

One other thing to keep in mind is that when a heat pump goes into the defrost cycle, it is actually going into the cooling cycle only. The outdoor fan stays off so the hot refrigerant gases can melt any ice that may be building up on the unit. This heat is being taken from the home you are trying to heat.

Guess what else happens? So you don’t feel the cold air from the cooling cycle, the good, old, reliable electric resistance heating element comes on to keep you warm. Does that sound very efficient? Of course not. That’s why, once again, I want to stress that in climates that drop below 40 degrees, the heat pump helper is the way to go.

This is what’s known as a hydro-air system. You can use a hot water heater or boiler to produce hot water. The hot water is piped to an air handler, sometimes called a fancoil. Inside the air handler is a multirow coil, through which hot water is circulated. Air is then passed over the coil and ducted to the living space.

You’ll be hard pressed to find a more comfortable and economical heat pump system in areas like the one I live in.

Here’s one more great advantage this system brings to your customers: If they are heating their domestic water with an electric water heater, which is expensive, they no longer need that; they can utilize the coil from a boiler or install an indirect storage tank. Or, of course, they could use a system like the one described earlier.

Mercurio is the owner and sole proprietor of Oil Tech Talk (, which offers the heating industry continued education through books, seminars, in-house training, and consulting. Mercurio is an associate trainer for Bacharach Inc., and he is the immediate past president and founder of the Susquehanna Valley Chapter of the National Association of Oilheating Service Managers (NAOHSM) and the current education chairperson.

Publication date: 05/19/2003