Heat pumps
An electric heat pump is one of the least expensive and most efficient ways
to heat and cool a home in our desert climate.
Here are answers to some frequently asked questions about heat pumps.
Please select a category from the list at the left.
A:
Q: We have a 1,600 square-foot house with a four-ton heat pump.
When the humidity is low, the house feels too dry, so I bought a humidifier which
spews about 1.5 gallons of water into the house in 24 hours. I keep the fan
running continuously. Am I damaging the heat pump or wasting electricity?
You are not damaging your heat pump by running the humidifier;
however, you are spending more by running the unit's fan continuously. If you assume
that your heat pump runs about 50% of the time during the hot summer months, then
your added fan operation is costing you approximately $10-15 a month.
Q: What type of routine maintenance does a heat pump need?
Mine is about five years old and I have done nothing with it so far.
A: You should have it serviced every other year, preferably
in the spring. This service will cost you about $60, but it will ensure that your
unit is running at its top efficiency and is mechanically sound.
About the only other thing you need to do is change the unit's filter inside your house.
A dirty filter will reduce the efficiency of your system, making it more expensive to cool
and heat your home.
The filters should be changed at least once a month -- unless you have a permanent type,
in which case you should wash it once a month. The filter is located behind the metal grill
where the air is drawn up into the unit, usually in a hallway.
Q: Can adjusting the registers in each room of the house really improve air flow?
My unit doesn't seem to be blowing enough air and I'm considering getting a new one.
A: Simply changing the registers will have little effect on air distribution.
You will have to rely on a contractor to evaluate your air distribution system to determine if
the amount of return area is large enough for the size unit you will be putting in. In a lot of
cases, the return air supply is too small and may need to be increased in order to allow for
proper airflow to the unit.
Q: When replacing a heat pump, should the air handler also be replaced, or is this
automatically replaced?
A: Roof-mounted heat pumps contain all the system components in the
single roof mounted cabinet. This means that the compressor, the air handler (indoor blower
motor and fan), the condenser coil, the condenser fan and motor, the evaporator coil and the
reversing valve are all located in the rooftop unit. Since all the components are located in the
single cabinet, the air handler will automatically be replaced when the unit is replaced.
With a split system, where the evaporator and condenser sections of a heat pump are
physically located in two different locations, both also should be replaced to achieve the
full efficiency of the new system. If you replace only one of the sections, the overall efficiency
of the system will be that of the old section and not the efficiency of the new section.
Q: I'm replacing a five-ton, roof-mounted heat pump. The unit should be $6,000 or less.
I also have a two-ton, roof-mounted 9 SEER heat pump that is also 12 years old. It is working fine.
I'm on the SRP Time-of-Use plan and am always looking for ways to reduce my electricity
consumption. What heat pump features are most likely to result in reduced maintenance costs?
A: New units have come a long way in reducing system operating and maintenance
costs. The use of improved coil materials and better coil design, as well as the development of the scroll
compressor, has increased the efficiency of heat pumps two-fold. All major brands of heat pumps will
provide you with 15-20 years of reliable service; however, the important thing to look for is efficiency.
SRP recommends a 13 SEER unit for good economical efficiency. Installing units higher than that typically
results in disproportionately higher up-front costs, while installing anything below a 13 SEER typically
costs you more to operate the unit than the savings in up-front costs is worth.
You mention that your old unit is a five-ton system and that you will be replacing it with another five-ton
unit. I recommend that you don't install a new five-ton unit simply because that is the size of your old one.
New units are designed to run more often and longer and therefore must be sized properly.
Before you sign any contract, make sure that your contractor performs a heat gain/loss calculation.
It is only by doing this calculation that the proper size system can be identified for your house.
A bigger than necessary unit will cost more to operate and maintain.
Q: I'm looking for a new heat pump for my 1,800-square-foot home.
My current heat pump is 16 years old. What SEER rating would you suggest?
A: SRP recommends a minimum 13 SEER; however, you should rely
on your contractor for advice on what SEER level is best for you. If you keep your thermostat
at a lower setting, therefore running your system more frequently and for longer periods of
time, you may want to consider installing a system with a higher SEER.
If we assume that the efficiency of your 16-year-old unit is about a 7 SEER, you could save
35 to 40% by installing a 12 SEER; 40 to 45% for a 13 SEER; and 45 to 50% for a 14 SEER.
To get an idea of how much money this equals, take your March bill (a month when typically
there is no heating or cooling) and subtract it from a summer month like June. The difference
is an estimate of how much you spent in June to run your air conditioner. Multiply this number
by the estimated percentage savings and you'll end up with an estimated dollar savings.
Do this for all the summer months and you'll have an idea of how much you'll be saving.
Use this estimate to decide whether the increase in efficiency is worth the investment.
Q: I have a 1,716 square-foot home with sunscreens on windows that face the
west side of the house. The house is 13 years old and well-insulated. What size heat
pump should I have?
A: My answer is based on a rule-of-thumb, but I absolutely do not
believe in this type of sizing estimate. The rule-of-thumb says that you should have
about one-ton of air conditioning for every 400 to 500 square feet of conditioned space.
For your house, you would be looking at about a four-ton system.
However, the only way for you to be sure that you are getting the correct sized air
conditioner is for your contractor to perform a heating and cooling load analysis.
When done correctly this analysis will identify the requirements based upon your
specific house and not some rule-of-thumb. You will actually be less comfortable
and pay higher energy bills with a larger-than-necessary unit. The ideal size for an
air conditioner is such that on the hottest day of the year, the unit runs continuously
and you're just barely comfortable in the house.
Q: I'm looking for a new heat pump and I've been told conflicting information
about the size of the unit. My house is 16 years old and currently has a 3.5-ton heat pump.
One person recommended getting a five-ton unit. Another company said that would not be
efficient and may cause humidity. What do you recommend?
A: Bigger is definitely not better. When a unit first turns on, it takes
about five to seven minutes for the system to reach steady state and its rated efficiency.
What happens with an oversized unit is that it turns on runs for about 10 minutes and then
shuts off. It never really has a chance to run at its top efficiency. You also pay more to
purchase a larger unit.
The only way to make sure that you are purchasing and installing the correct size unit is
to insist that a contractor performs load calculations on your house.
Q: Are geothermal heat pumps/water furnaces available in the Phoenix area?
They're fairly common in the Midwest.
A: The systems you are referring to are called ground-source heat pumps.
They use the earth as the condenser section of the unit instead of relying on ambient air to
dissipate the heat.
While this technology is quickly being accepted in other parts of the country, it is very rare
in the Phoenix area. A good source for equipment and information is
Waterfurnace International.