I'm looking for a house to buy in the South Carolina low country, where average lows in January get down to just under 40 deg F and highs in the summer get to just over 90 deg F. The houses in that area seem pretty evenly split between "gas and central A/C" and "heat pumps" for heating and cooling. I'm not sure which one is better.

I have read that "heat pumps operate optimally at approximately 45-50 degrees" (that source could be biased but I've seen similar numbers other places) - would it be right to conclude that heat pumps are more efficient than gas for my location? Or maybe a better question, how can I measure efficiency? Mostly I care about my utility bill, after all. Cost of gas and electricity obviously will change over time so I know I can't ask which is absolutely cheaper, but it seems that the most efficient of the two should "win."

Other factors I'm considering are long term cost and speed. I don't want to have to replace a major fixture every year. Is there a big difference in average "lifespans" between gas and heat pump? And I have heard stories that gas produces hotter air than heat pumps. Does it make temperature change noticeably faster as a result? In other words, if I'm cold, I don't want to wait four hours for the temperature to go up a degree.

C'mon Stack Exchange - you can do better than Yahoo! Answers did right?

  • Peak efficiency and ability to function are entirely different - heat pumps around here go into heating cycle down to around 15F. Keep in mind your source is in Minnesota... – Comintern Apr 10 '14 at 2:44
  • Also, if the up-front cost isn't as important you might consider a third option - a ground-source (geothermal) heat pump. You're in an ideal climate zone for it and if you can afford the installation cost they are vastly more efficient than either the gas/AC or heat pump option, low maintenance, and cheap to operate. en.wikipedia.org/wiki/Geothermal_heat_pump – Comintern Apr 10 '14 at 3:01
  • The company I worked for did a study on the cost of geothermal over its lifespan, compared to regular heat pumps. The findings was that when you break up the cost of the install, operating costs, over its potential lifespan, the amount out of pocket was about a wash. My previous employer was always suggesting to go with geothermal, if you wanted the best, etc., but after the study, the CEO/COO did not after that study. He is the one who did the study. – Jack Apr 10 '14 at 3:46
  • @Jack That doesn't really surprise me, but it might still be worth getting a quote. The installation costs can vary wildly depending on the system being replaced (i.e. is there ductwork, how large of a ground loop/well field is needed, etc). Also regional differences in heating/cooling demands, electricity and gas pricing, the heat loss characteristics of the structure, etc. are going to contribute to the ROI. The house I'm in now would roughly break even too (difficult loop installation), but there are several houses around town that have had them pay for themselves over 5-10 years. – Comintern Apr 10 '14 at 4:20

It's illogical to compare the efficiencies of gas to heat pump systems because the way they produce heat is completely different. One directly burns fuel to produce heat, the other consumes energy only to move heat around. The source heat for heat pumps is essentially free. Thus calculating heat pump efficiencies will yield numbers well over 100%, something gas can never do.

In addition, if you really want to determine the root energy impact of each system, you need to consider the efficiencies involved in producing the energy and delivering it to your home. This will vary greatly by how each energy form is produced. Hydroelectric has a very different efficiency than coal fed power plants. Some utilities vary the source of power seasonally and through the years, so the root number is a moving target.

While it is true energy costs fluctuate, it still makes the most sense to compare your actual direct costs from using each system. While the actual cost of energy will vary significantly through the years, unless there is a major change in your area regarding sourcing each type of energy, the relative costs of each type should not vary nearly as much. When comparing costs, you must consider installation costs, maintenance costs, and eventual replacement costs. Comparing only direct operating costs can be very misleading.

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This completely depends on the cost of fuels in your area, and the specific equipment being used. If gas prices are low, you could save money using a fuel fired furnace.

A heat pump uses electricity for both heating and cooling, so you'll only have to consider the electrical consumption.

A furnace and A/C system uses electricity for cooling, and a combination of fuel and electricity for heating. Which makes the calculations a bit more complex. Not to mention, natural gas furnaces come with many different efficiency ratings.

It's impossible to compare two different systems, without knowing more about the systems being compared. Shop around for both. When you decide on one of each, compare them, and pick the one that works best for you.

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