One of the most common questions we get from homeowners involve the HVAC (heating, ventilation, air conditioning) system. The question: “What the heck is a heat pump?”
A heat pump is an all-electric system (no gas or oil) and it can either cool or heat your house. When operating in cooling mode it’s just a standard AC system; in heating mode it’s an AC system in reverse. As you’ll see on your utility bill, the obvious difference between a heat pump and a gas or oil system is the heat pump has a higher electric cost.
Now to the science of it… Just like a standard AC system, the heat pump has interior and exterior components. These contain coils which allow refrigerant to condense or expand as it flows through a series of pipes. The outside component uses electricity to pressurize the fluid; the change of pressure creates a drastic change of temperature and the fluid will either absorb or expel heat in order to reach equilibrium with the air around it. In the summer, the fluid will absorb heat from inside and expel it outside. In the winter, it will absorb heat from outside and expel it inside. Yes, believe it or not, you can pull heat from outside winter air to heat your house. But there are limits to this magic! If the winter weather is very cold, say in the low 20s, it becomes increasingly difficult to gather enough heat from outside, and the heat has to be supplemented with direct electrical heat (like a giant hairdryer). This form of heating is less efficient, resulting in higher electric bills than when the heat pump is working in normal mode. In summary, with mild winter temperatures the heat pump is very efficient, but as it gets down in the 20s, it becomes less efficient. For most years this variation averages out to be a viable HVAC option in the DC area but on any given year you may have noticeably higher (or lower) winter electrical bills.
If you’re shopping for a home, we recommend asking your home inspector what type(s) of HVAC system is present and have them explain the benefit and limitations of each.
