Heat Pumps stink. Well Sorta…..
Heat pumps are great, In the correct application
I’ll start with the fact that I love heat pumps. They are extremely efficient in mild weather, and are getting higher BTU outputs in lower temperatures than previous models. But I also must admit that I don’t like heat pumps. As the temperature falls, so does the efficiency and output, while the structure needs more BTU’s.
Heat pumps have been around as long as A/C units have been, so the concept is nothing new. In fact, a heat pump is nothing more than an A/C unit running backwards. The units have however made great strides in advancing efficiency, output and dependability over the last several decades. Even with all the advancements, heat pumps still suck in Ohio’s climate, for most homes. But you have probably been hearing more and more about them, as policy makers make a push for more electric heating as they attempt to move to a smaller dependency on carbon based fuel sources. So let's take a look into what I like and don't like about heat pumps!
The biggest issue I have with heat pumps and Ohio, has nothing to do with our temperatures, and everything to do with home construction. Prior to the early 2000’s, the home building industry pretty much sucked when it came to air sealing and great insulation. As a result, homes need much more heating BTU’s than cooling BTU’s. Take a 1970’s tri level we recently did a load calculation on. At our design conditions, the home needed 50,000 btu of heat and only 22,000 btu of cooling. A 4 ton heat pump is rated for 48,000 btu at 47* outside temperature and only 22,000 btu at 5*, which is the complete inverse of the heating BTU required. As the outdoor temperature falls, the temperature of the air coming from the vents also falls, causing the air to feel less comfortable. On the cooling side of the equation, the same 4 ton unit is going to produce roughly 46,000 btu of cooling yet the house only needs 22,000 btu, thus leading us to a horribly oversized a/c unit. A 2 stage unit can slightly help on the cooling side of the equation by running in low stage, but we still have the inverse output problem for the heating side. In most older all electric homes that have heat pumps, we are forced to rely on back up heating elements that are expensive to run. But with many older neighborhoods in our region, electric is the only choice, so we are forced to stick with heat pumps. That is why we always like to suggest easy upgrades like attic insulation and weather sealing when appropriate, to reduce the heating needs of the house.
Now to the bright side of heat pumps!
They are incredibly efficient, in mild weather. A base model 15 SEER2 heat pump can have a coefficient of performance of 3.3 at 47*. Meaning for every 1$ of electricity used to run the system, it will generate 3.3$ worth of heat. A high efficiency gas furnace has a cop of .96. But at 5* the same HP has a COP of 2. While that sounds better than the gas furnace, take into consideration the cost of electricity versus the cost of gas. With inverter based technology, heat pumps now are able to have higher outputs at lower temps than standard heat pumps. While this is a great improvement, they still lack the total output needed on the coldest of days.
The biggest plus for heat pumps in Ohio is improved building and air sealing. Take a house we are currently in the design phase of. The cooling load is 32,000 btu and the heating load is 35,000 btu. That smaller gap allows us to pick units that are better suited to handle both heating, cooling, and dehumidification more reasonably. Reducing the overall load requirements of the house with increased insulation and air sealing also reduces the amount of electric resistance heating, thus lowering our overall electric consumption used for heating.
Heat pumps really are great, when put in the correct application. I myself even have a heat pump in my home. But it’s important to understand both the pro’s and con’s of heat pumps.
Have a heat pump question, or any question in general, just drop a note below!!!
Happy Heating!
Ben Haws
JBH Heating and Air
