By Andrew Lake
What is an air source heat pump?
An air source heat pump is basically a whole-house air conditioner that can operate in reverse. It can move heat into the house in the winter just like it moves it out in the summer. A heat pump can absorb heat from colder outdoor air and release it into the warmer indoor air, just like your refrigerator removes heat from the inside where your milk is and blows it out the bottom.
The efficiency of an air source heat pump is very high during milder winter days. When the temperature outside is only a few degrees cooler than room temperature, they can operate at about 450% efficiency. This means that every watt of electricity you pay for creates 4.5 watts of heat energy!
Unfortunately, efficiencies drop down to about 200% at freezing, and the heat pump has little ability to produce heat at temperatures below 25F. This means that your current heating system should be kept to warm your house on the coldest days of the year.
How much can I save on energy with one?
How much you can save depends on several factors:
Electricity rates in your area
Heat pumps run on electricity and are most economical in areas with lower electricity prices. A comparison of average electricity prices for each state can be found here.
Current method of heating
Natural gas, the most common energy source for heating in the United States, is also the least expensive. If you are currently using electricity or oil then you have greater potential for savings. If you are currently using an older, less efficient system you will also have greater savings potential. An explanation of how to compare the HSPF efficiency rating of heat pumps to the efficiency ratings of oil and gas systems can be found here.
Size of house
A 4,000 sq. ft. house will probably cost almost 4 times as much to heat as a 1,000 sq. ft. house, but a heat pump that has 4 times the heating capacity should cost less than 50% more. A heat pump is generally a better investment for larger homes than smaller ones.
Size of ducting and electricity supply
Heat pumps work best in homes with larger ductwork and power supplies. Ideally, a heat pump will have about 5,000 watts of power and more than 5 registers for every 1,000 sq. feet of space to heat. Some very old houses don’t come close to having this much power and venting available, so a heat pump will not be nearly as effective.
An air source heat pump is ultra efficient on milder winter days but is of little use when it is way below freezing. They are less attractive in areas with very cold winters and lots of snowfall.
In general, heat pumps are attractive in the Pacific Northwest because of the low electricity rates and mild winter weather. They are also attractive to many Northeastern homeowners who are currently using expensive oil to heat their homes. Despite their low heating costs, many Southern homeowners would be wise to invest in a heat pump when their air conditioner needs to be replaced. They only cost about 20% more than an AC unit.
Unfortunately, they aren’t as appealing in the Mountain and Midwestern regions, because of moderately high electricity costs and colder winters. Some of these residents may be attracted to geothermal heat pumps. They are the most efficient way to heat your home and are effective even on the coldest winter days. Check back for a post on these soon.
Andrew Lake is a licensed heating and air conditioning technician with Shell Busey's HouseSmart Heating and Air Conditioning in Vancouver, Canada.
The next installment in this series will cover Geothermal Heat Pumps.
FIRST IN A SERIES ON ENERGY SAVING HEATING and COOLING SYSTEMS
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