December 22nd, 2015

What You Should Know About Heat Pumps

Home Owners Network

Many homes are equipped with heat pumps as their heating and cooling system.  Heat pumps work well at most temperatures; however, in extreme temperatures they may not provide the comfort level you expect.  The following are some operating and maintenance tips to help you set realistic expectations about heat pumps and to maintain the system at peak energy efficiency and operating effectiveness.

Heat pumps absorb heat from one place and transfer it to another.  In air conditioning mode, they absorb heat from inside the home and transfer it outside.  In heating mode, they absorb heat from outside and transfer it inside.  This process works well when the outside temperature is between about 30˚ and 95˚ F.  It is more difficult for the system to maintain comfortable interior temperatures when the outside temperature is beyond this range and when the humidity is high.  Older systems and systems that are poorly maintained may have a narrower outside temperature range within which they can maintain comfortable interior temperatures. 

Jan-2015Heat pumps, and all heating and cooling systems, should be correctly sized for the home.  A common misconception about heat pumps is that a larger system is better.  In fact, too large is bad.  A heat pump that is too large may not run long enough in air conditioning mode to effectively remove humidity from the air.  This can create moisture control problems that can contribute to mold growth.  A heat pump is less energy efficient when it begins operating and does not reach full energy efficiency for several minutes.  A heat pump that runs for short periods costs more to run and may have a shorter service life.

 Heat pumps are less effective in very cold weather.  This is why they are less common in northern areas.  When the outside temperature falls below about 30˚ F., a heat pump may not be able to raise the internal temperature to a comfortable level.  Heat pumps in cooler climates should be equipped with auxiliary heating elements.  These elements look and act much like the wires that glow red in a toaster.  Like their cousins in a toaster, these elements provide additional heat to help bring the inside temperature to a normal level.  Because it is difficult to know if these elements are operating properly, you should have them tested as part of normal system maintenance.

A heat pump should maintain a comfortable indoor temperature. Reasonable temperature expectations are 68˚ F in heating mode and 78˚ F. or 15˚ F. below an outside air temperature of 95˚ F in cooling mode.  Temperature should be measured near the center of the room and about five feet above the floor.

Use of setback thermostats is generally not recommended with heat pumps, particularly in heat mode.  Heat pumps, especially older ones, may be designed so that in heating mode the auxiliary heating elements will activate if there is a difference of about 3 or more degrees between the thermostat setting and inside air temperature.  The heating elements are far more expensive to run than the heat pump itself, so use of the heating elements should be avoided.

Heat pump maintenance starts with regular filter replacement.  If you choose disposable filters, use the inexpensive blue or white fiberglass mesh type.  The more expensive pleated paper filters can restrict the air flow in the system making it work longer.  Change filters every month.

If you have an access tube in the condensate drain pipe at the air handler, pour about ½ cup of bleach into the line when you change the filter.  This will help keep the pipe clean and reduce the chance that it will clog and force water into your home.  If you do not have an access tube, consider having one installed at the next service call.

Use a garden hose to wash the fins on the condenser (the outside unit) about twice per year.  Keep walls and plants at least 1 foot from the sides and 6 feet from the top of the condenser.  Keep the condenser shaded from direct sunlight to the extent practical.

Finally, have preventative maintenance service performed on the system at least once per year.  Spring or fall are good times so both heating and cooling modes can be tested.

Like all mechanical components, heat pumps wear out.  Condensers typically last about 15 years.  Air handlers typically last about 20 years.  You should replace both units when one wears out.

The Bottom Line

Heat pumps are a good choice for heating and cooling in warm climates where gas service is not available.  A gas furnace is usually a more cost-effective choice where gas service is available.  Heat pumps can provide energy efficient service for many years when properly installed, operated, and maintained.

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