There are 2 main types of heat pumps: Air source and Ground source. This article mainly compares and air source heat pump to a natural gas furnace. We like the EnergySavers.Gov page on how a Heat pump works. The biggest drawback to heat pumps is that in cold climate they probably will need supplemental heat, because they can't pull any heat from the outside air if it gets too cold.
In our post "Heat Pump - will an air-source work for you" we stated:
The state of California has a good description of air conditioners and heat pumps on their Energy Quest site (even though it looks like it is made for kids it has some great explanations):
"A heat pump is an air conditioner that contains a valve that lets it switch between "air conditioner" and "heater." When the valve is switched one way, the heat pump acts like an air conditioner, and when it is switched the other way it reverses the flow of the liquid inside the heat pump and acts like a heater."
The DOE Energy Savers Heat Pump guide has a great introduction to what a Heat Pump is and where it works:
"For climates with moderate heating and cooling needs, heat pumps offer an energy-efficient alternative to furnaces and air conditioners. Like your refrigerator, heat pumps use electricity to move heat from a cool space into a warm, making the cool space cooler and the warm space warmer. During the heating season, heat pumps move heat from the cool outdoors into your warm house; during the cooling season, heat pumps move heat from your cool house into the warm outdoors. Because they move heat rather than generate heat, heat pumps can provide up to 4 times the amount of energy they consume."
My biggest question with this opening paragraph is what defines a moderate climate? While this isn't defined by Energy Savers in their heat pump section, they do touch on it in the Heating with Electrical Resistance section:
"If electricity is the only choice, heat pumps are preferable in most climates, as they easily cut electricity use by 50% when compared with electric resistance heating. The exception is in dry climates with either hot or mixed (hot and cold) temperatures (these climates are found in the non-coastal part of California; the southern tip of Nevada; the southwest corner of Utah; southern and western Arizona; southern and eastern New Mexico; the southeast corner of Colorado; and western Texas). For these dry climates, there are so few heating days that the high cost of heating is not economically significant."
But I think Energy Savers was a bit conservative in listing areas where heat pumps don't work so well. From their air-source heat pump page they state:
"When outdoor temperatures fall below 40°F, a less-efficient panel of electric resistance coils, similar to those in your toaster, kicks in to provide indoor heating. This is why air-source heat pumps aren't always very efficient for heating in areas with cold winters. Some units now have gas-fired backup furnaces instead of electric resistance coils, allowing them to operate more efficiently"
When discussing which technology is best for heating our homes in his latest post on The Shocking Truth About Heat Pumps, home efficiency expert Allison Bailes states:
"The truth is that anyone who says never or always is usually wrong, especially when it comes to which products, materials, or technologies to use in your home. In the case of gas heating versus heat pumps, here are some of the issues you need to consider:
- Climate zone
- Electricity vs. gas rates and service charges
- Where your electricity comes from
- Building enclosure
- Modern equipment"
And closes with:
"Heat pumps today aren't the same as the early models from the 1970s and '80s. They're more efficient. They've got the supplemental heat thing figured out. And they come in a wide variety of efficiency, capacity, and technology, from the standard models to mini-splits to ground-source heat pumps.
Of course, furnaces (and boilers) have come along, too. We now have high-efficiency, sealed combustion furnaces that can distribute the heat through either forced air or hydronics. You can get a modulating condensing (mod-con) furnace that can adjust the capacity closer to the needs of the house.
Overall, it's easier and less expensive to get a heat pump small enough to match the loads of a high performance home than it is to get an appropriately sized furnace. Mini-splits are great for this and allow for better zoning, too.
In the end, you shouldn't go with a furnace just because an expert said all heat pumps are unacceptable. You've got to look at the issues I outlined above. Consider what your priorities are. Low energy bills? Environmentally friendly energy sources? Uniform heating with lower temperatures or short blasts of higher temperatures?
The shocking truth about heat pumps is that they might well be a great fit for your home. Or they might not. It depends."
Heat pumps and hydronics - A great team for high performance homes
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