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Ask Mr. Tight-Watt: single-stage vs. two-stage air-source heat pump  Smart Choices Archive

Ask Mr. Tight-Watt: single-stage vs. two-stage air-source heat pump

A heat pump is an excellent choice for heating and cooling. But which is best: Single- or two-stage models?

Energy Efficiency: Heating, Cooling, Ventilation

Mr. Tight-Watt answers questions about energy efficiency for our readers of our Smart Choices e-newsletter. This month, he asked two experts to weigh in on a question about air source heat pumps.

Jack Schoon is energy advisor for Iowa Lakes Electric Cooperative, Estherville. An expert from Questline, a resource for RECs which provides technical information on a variety of issues, also responded.

Question: I'm considering installing an air-source heat pump in my home in northern Iowa. Should I install a two-stage air-source heat pump or a single-stage? My contractor says a single-stage will work, but can't explain why. Can you help? –Robin, a Smart Choices reader

Jack Schoon: The single-stage heat pumps are efficient; the level of efficiency depends on the SEER (Seasonal Energy Efficiency Ratio) rating and the HSPF (Heating Seasonal Performance Factor) rating. The higher the ratings, the more efficient the unit is. However, keep in mind that the cost of installation goes up along with the ratings, so it’s important to weigh the cost vs. benefits. Single-stage units have a good track record because of the many years that they have been in the marketplace.

Two-stage heat pumps are very efficient also. These units achieve highest efficiency when running on low speed. When the outdoor ambient temperature changes and your home requires more BTUs – whether in heating or cooling – the unit senses the change and shifts into high speed to produce more cooling or heating, depending on the season.

These units have SEER and HSPF ratings also. The higher the ratings, the more efficient the unit is. Again, though, higher ratings have a higher installation cost.

In our part of the country, the two-stage heat pump allows the heating dealer to size the unit closer to the heating needs of the home; the end result is that the supplemental resistance heat will not be used as much as it would be with the single-stage heat pump. This may be the deciding point for homeowners to choose a two-stage heat pump, even though a two-stage unit costs more. That’s because the most expensive component to operate is the resistance heat portion, and depending on the winter (how cold and for how long), the two-stage heat pump may make economic sense over the life of the unit.

Questline: The decision on whether to install a single-stage or a two-stage air-source heat pump is a trade-off between cost and comfort.

A two-stage heat pump will cost more to purchase but will cost less to operate. The two-stage blower and compressor combination will also provide more even heating and cooling. You would experience some improved comfort, but not a dramatic difference. Considering your relatively cool climate zone, you would probably best be served by a single-stage heat pump with a premium thermostat. Compare the cost differential with the benefits.

Questline recommends this additional information:
• Maximum Comfort and Energy Savings with Two-Stage Heat Pumps
• Two-Stage vs Single-Stage AC

Ask Mr. Tight-Watt a question or view other questions he has answered.






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