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How to determine efficiencies of electric heating systems?

  1. Aug 12, 2017 #1
    I am building a house and would like to understand how to perform an energy balance/efficiency calculation on various electrical heating systems
  2. jcsd
  3. Aug 13, 2017 #2
    They all convert 100% of input energy to thermal energy. If they are forced air there is a tiny amount used for air circulation. But even the waste heat of the blower motor adds to the heating.

    If you are in a mild to moderate climate, radiant heating, is adequate. This is often done with relatively low temperature baseboard heaters with a thermostat in each room. In harsher climates (think snow country with many feet of snow per season), radiant heating bothers some people because they are warmed but are often breathing somewhat colder air; at least in older houses. A new build with lots of insulation and double- or triple-pane windows would make this less of an issue.

    In the harsher climates, forced air heating (usually central) may be more comfortable than radiant.

    Electric heaters that operate at higher temperatures (i.e. portable electric heaters) can be useful in harsher climates because their higher temperature moves hot air around by convection.

    Be aware that electric heat is often the second most expensive option, with propane costing even more. Also consider the reliability of the electric supply.

    Oh, I just looked at your profile page. Looks like you are in one of those "harsher climates."
  4. Aug 13, 2017 #3


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  5. Aug 13, 2017 #4


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    While all electric resistance heaters are 100% efficient, heat pumps are in effect much more than 100% efficient (up to 4x)...though the efficiency depend on the temperature of the source reservoir (air or water).
  6. Aug 13, 2017 #5
    Thanks for your reply - it is most helpful in determining the appropriate heating technology for my geography.
    I assume that there is a formula (s) to determine efficiency of the system, based on input energy vs output heat?[/QUOTE]
    Last edited by a moderator: Aug 13, 2017
  7. Aug 13, 2017 #6
  8. Aug 13, 2017 #7
  9. Aug 15, 2017 at 4:01 PM #8


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    Presumably that's Propane in cylinders? Here in the UK you can get LPG (bulk Propane) delivered by tanker and it works out at around 6.13p/kWH compared to Electricity at around 18p/kWH and heating oil/kerosene at 4.11p/kWH. By the same measure electric heat pumps deliver heat at around 5-7p/kWH.

    So "raw" electricity is around three times more expensive than most alternatives for us unless you use a heat pump.

    See "Pence per kWh (after boiler efficiency)"
  10. Aug 16, 2017 at 12:53 AM #9


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    A heat pump will give a factor of three advantage over a resistive heater. The problem is finding dry air or liquid ground water to extract heat from. When the cooling air is near freezing point the heat exchanger will ice up and force an inefficient defrost cycle.
  11. Aug 16, 2017 at 1:37 AM #10


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    Fortunately here in the UK the air is usually drier in winter than summer.

    Most modern GSHP are also closed loop/sealed and don't rely on ground water. This also has the advantage of reducing corrosion as the loop can be dosed with corrosion inhibitor.
  12. Aug 16, 2017 at 2:40 AM #11


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    Any evaluation of heating methods and efficiencies really needs to take into account the thermal properties of the building that is being heated .

    In an old style house design with poor insulation the efficiency of heating devices matters a lot because you need a lot of heating .

    In more modern houses which are much better insulated the efficiency of heating devices matters less because you need much less heating .

    In the limit some houses which have been built in the uk in recent times are so well insulated that very little heat is needed at all and efficiency of heating devices no longer matters .

    Any evaluation of heating costs really needs to be done on a long term basis and take into account the trade off between cost of running heating devices and the cost of making the house (on initial build or by retrofit work) need less heating .
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