Heat pumps (space heating)

Heat pumps have been gaining in popularity in recent years due to rising energy prices and falling technology costs. As most people probably know, a heat pump can provide a substantially greater amount of heat than the electricity it consumes simply because it just moves heat around instead of generating it. The resulting ability to operate at 200%, 300% or even higher efficiencies gives heat pumps quite a bit of cool cleantech appeal.

air source heat pump cycle

However, heat pumps are far from a slam-dunk choice for home heating and are actually only the best option for people living in large open-plan homes located in mild climates who value tight temperature control very highly. This post will explain the reasons behind this narrow customer focus in a little more detail.

The most basic problem with a heat pump is that it loses efficiency as the outside temperature decreases. In other words, as you need more heat, the heat pump produces less heat. The graph below tells the story.

heat pump design temperature

Generally, if the outside temperature regularly drops below freezing where you live, heat pumps are not a good idea. You can install a dual system where the heat pump gets supplemented by another heat source when it gets very cold, but it will be difficult to justify the added costs and complexity in this case. Those living in cold climes will therefore get more value from a standard furnace system.

When comparing to a gas furnace, an air-source heat pump will generally cost about the same both in terms of up-front investment and running costs. More efficient ground-source heat pumps will have somewhat lower running costs, but mostly have a prohibitively large upfront cost. Running costs of different heating options in the US can be viewed in this regularly updated Excel sheet from the EIA.

If the electricity in your area comes mostly from fossil fuels (as in most places), the CO2 emissions from a heat pump will also be similar to those from a furnace. The difference is, however, that the furnace can stand alone while the heat pump will need backup at times when it is needed most. Furnaces also have much longer lifespans than heat pumps.

Effective use of a heat pump also requires an open plan design so that the heat can freely spread through the home. In this sense, electric panel heaters can be better to heat only single rooms as required instead of heating the entire home. If you are willing to follow such a modular heating strategy, simple and cheap panel heaters can actually work out cheaper than a heat pump because you will generally be heating a much smaller space.

One potentially handy feature of a heat pump is that it can serve both as a cooling and heating unit. However, this functionality is not required in many locations unless you really are extremely sensitive to temperature differences.

In general, heat pumps work best in moderate climates and when it is used a lot (to retrieve the initial capital investment over a typical 10-15 year lifespan). As far as I can see, a much better strategy in such moderate climates is to simply put on an extra sweater when it gets a little cold or turn on a fan when it gets slightly hot. If you really value the luxury of perfect temperature control, however, a heat pump can be a good choice.

Filed under: Consumption patterns – The green economy

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