Heat Pump Basics Explained

I don’t often have customers who want to follow me during the entire home inspection. It takes about three hours and leads me places that not everyone wants to visit, for example on the roof or in the crawlspace or attic. When they do want to tag along I try to make the experience educational and enjoyable. There are many components of the home that most people don’t know much about and the inspection is a great place to learn. This is especially true for first time home owners. I enjoy all their questions and appreciate the opportunity to teach them about their new home.

I often get the question “how does the HVAC system work” or even more basic “what does HVAC stand for”. I respond sympathetically because I can understand how perplexing the heating, ventilation and air conditioning (HVAC) system can be. I can’t think of any other system in the home that is more difficult to understand or to explain.

Here in North East Florida we get just enough cool weather that occasional heat is necessary. Subsequently almost every house, regardless of age, has a split system heat pump. Electric heat pumps are characterized by transferring heat rather than burning fuel to create it. This type of system has an inside air handler containing an evaporator and a circulation fan and an outside unit containing a compressor and a condenser. These two units are connected by two refrigerant lines made of copper pipe. One of these pipes is larger than the other and should always be insulated. This type of system can provide both air conditioning and heat so it’s the ideal system for our First Coast climate.

The system’s operation starts when you select the temperature at your thermostat. For the sake of discussion, let’s imagine that it’s July and you’re turning down the air condition. The refrigerant is in a liquid state and it’s very cold. It enters the evaporator coil in the air handler and cools the coils. Meanwhile, the air in your home is circulating. It comes out of a supply vent dropping first as cool air and later rising as it warms only to get sucked back into the system at a return vent. It makes its way through the duct-work and then passes over the same evaporator coil that the refrigerant has cooled. At this point heat from the air is extracted, cooling the air. The circulation fan then sends the cool air back through your duct-work to again cool your room. The heat that was in the air has now been absorbed by the refrigerant, turning it from a liquid to a gas as it heats up. This gas then travels through the smaller of the two pipes out to the compressor.

When the refrigerant gas enters the outside unit’s compressor it is pressurized. This increases the temperature of the gas even more to a point much higher than the air outside of the house. The gas then travels over the coils of the condenser. This step releases the heat gathered by the refrigerant and turns the refrigerant from a hot gas back to a cool liquid where it then enters your house again through the larger, insulated pipe, ready to start the process again.

That’s a very basic description of the parts and the process that your split system heat pump uses to cool your home. To produce heat, the system simply runs backwards, gathering heat from the outdoor air and using it to warm the indoor air.  This explanation is usually perfectly acceptable and understandable for the new home owners who are following me on an inspection. There is definite satisfaction in knowing how something works, and it’s this knowledge that helps with the second lesson: knowing how to take care of it.

According to the International Association of Certified Home Inspectors (InterNACHI), the service life expectancy of a heat pump in Florida is 12-15 years. What I tell new home owners all the time is that you may be able to add a few years to this with proper maintenance, and that neglect will certainly mean replacing the system early. It’s also true that much depends on where you live. Salty beach air tends to degrade the metal housing and the internal parts much quicker than inland air.

But no matter where you live you should follow a regular maintenance plan that begins with changing the air handler air filter monthly. Clean filters are easier for the circulating fan to move air through, meaning the machine won’t need to work as hard to draw air. Clean filters also help to keep the coils free of dirt and dust; meaning less contaminates in the air circulating through your house. It’s also important to keep the condensate drain flowing freely. This is the pipe that drains the condensation that your air handler creates away from the unit and typically outside of your house. This pipe has a tendency to become clogged with algae. InterNACHI recommends keeping them open by pouring a quart of bleach followed by a gallon of warm water down the drain line every three months. Outside at the condenser it’s important to keep the area around the unit clear of obstructions. Ideally three feet of clearance should be maintained so air can evenly be pulled to the unit and to keep the inside of the unit free of leaves and other debris.

Lastly, the most important thing you can do is to have the system serviced every six months by a qualified HVAC technician. By doing this you may be able to save in repairs and delay replacement by many years.

1 Comment

  1. Joleisa on October 22, 2017 at 10:47 pm

    I must say that I fit the description of most people when it comes to these set up in homes. I’m curious… but not very. I’m very happy for people like you who understand these and know exactly what you are doing. Thanks for the advice about getting it serviced every six months though, I’ll take that.

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