One of our readers asked us this question - we'd love any feedback you have:
For the climate in Denver, do air source heat pumps with natural gas furnace backup make sense from an energy savings and economic (operating costs) perspective?

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This is the system we have (we live in PA).  For the last 12 - 13 years.  It has given us flexibility.  Natural gas is cheaper than electric here.  When they ran the main through our neighborhood, we got a line run into our house free with an agreement to put in a water heater.  We use our heat pump in the summers for central AC and when one or the other unit needs service or a part we can switch over to the other.  When the electric rates were "deregulated" here and the costs jumped up we just used our gas unit (a 90 +) more.  Natural gas rates have actually gone down in PA because it's a publicly held utility so for us it's a savings.  The other thing I have done since I got training in energy auditing is to thoroughly go over our home and tweak the sealing and venting.  Our last projects were to deal with all the panned returns in the house and remove the trim & foam around windows on the windward side of the house (a 1990's build which is wrapped but not foamed at the window penetrations)  -- a note on central AC -- we lowered this energy usage by installing a ceiling fan in the bedroom and family room and we do use small window fans until it gets too hot and room darkening shades on the sunny side of the house.  Several areas of the house are more comfortable than they were and the temperature is more constant.  The cost over the last 10+ years has gone down a little instead of up dramatically.

Need more data:

0) Compared to what?

1) Are you in Denver or somewhere nearby but at a significant altitude difference that influences microclimate?

2) Winter cost per kwh...any difference if electricity is primary heat source

3) Are we talking code minimum heat pumps or more efficient systems. Premium variable speed systems are significantly more efficient

4) Cost of natural gas?

In our area payback time for a Dual Fuel system exceeds the expected lifetime of the equipment. Most homeowners give up on the heat pump the first time they feel the warmth of the gas heat.

Thank you for your responses! Curt, the reader didn't offer additional information, but I will pass along your questions as items that need to be considered before making their decision.

An ASHP makes all sorts of economic sense.  I installed one at my home and had a significant reduction in usage.  I did some air sealing and insulating also.  My unit also has a Dual Fuel set up, so it has the NG furnace for back up.

My ASHP is set to flip over to the gas furnace somewhere around 18 - 22 ° F.  Think about how many hours of heating in a typical winter you do above that temperature and how much you do below it.  I have a 5° F winter design point. Denver is only 8° lower.  If you are outside of Denver check closely, because the altitude will make more change in these considerations.

You can have someone do an energy model on your home to get some better figures.  So start with an Energy Audit and a Manual J load calc.  Look a the home as it exists now, and after you do some other recommended improvements, such as insulation and air sealing.

Do you currently have NG heat?  If so, be prepared for a change.  ASHP warm the 70° return air to 85 - 90°.  A new gas furnace will warm the air +35° or 105° .  If you want that blast of warm air when the heat comes on, you will not like the ASHP.  If you can adjust to that change (it is a big one, be careful!!!) you might be a candidate for an ASHP.

The heat pump is more efficient than a furnace because it uses Energy to move heat, it does not convert the energy to heat.  Heating the heat exchanger to 105° takes energy, with no heat going in the house.  Then when the burner quits, the heat left in the heat exchanger doesn't help either.

This reader needs to get some more info.  Probably best to visit with some folks that use ASHP.

I have a mini-split in Connecticut that does a reasonably good job of heating my first floor with an open floor plan for good air distribution. I heat with oil (hydronic) with the highest electrical rates in the US and my operating cost running 24x7 is approx $10. per month. The inverter technology in todays units means a high SEER and very low electrical (DC) usage. Most manufacturers offer a "A" coil type setup for retrofitting in an existing air handler. Mine is a more typical wall mounted head unit.. What has gotten my attention is the ECODAN unit by Mitsubshi which is marketed in Europe.

As mentioned, heat pump temperature output is much less than a typical oversized gas furnace which is sized for poorly insulated/air sealed homes- homeowners expect a hot blast from the registers to quckly heat the area. The low operating costs of inverter heat pumps make them excellent for the shoulder months with lower heating requirements.

 

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