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Is it more efficient to heat a bedroom with whole house's forced-air natural-gas burning furnace, or only an electric space heater in the bedroom?

For a very location-specific application, electric space heaters seem like an efficient option just by virtue of focusing the energy of heating on an easier area to heat. Especially with an older, draftier house that probably loses heat throughout the forced air delivery system, as compared to a warming space heater right at the toe of the bed or something.

Adding to this, electricity can be sourced from renewable sources, which can't be said for the fracked natural gas fueled furnace. So shifting energy use onto electric serves as a divestment from fossil fuels and an investment in renewables.

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    Consider adding a thicker blanket to this comparison. – Jean-Paul Calderone Oct 29 '18 at 12:40
  • Your questions tend to have a bias to the answer you want. – paparazzo Oct 30 '18 at 0:46
  • @paparazzo sorry if they come off as loaded questions. It may be because I already have an intuition and some reasoning behind a particular answer when I ask the question, but I'm looking for a more solid basis for the answer (or to find that my guess is wrong and it's a different answer). – cr0 Oct 30 '18 at 13:32
  • But your intuition skews the question. Is the assumption this is a drafty house. Not all natural gas is fracked. – paparazzo Oct 30 '18 at 17:31
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    The energy requirements could actually be calculated (not by me) if you gave dimensions, temperature differences and insulation coefficients of the room and the building. That would make it a better question. Currently answers will be largely guesswork. – Jan Doggen Oct 31 '18 at 13:07
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In terms of energy-efficiency within your own home (i.e. when we ignore energy losses outside the home), it will almost certainly be more efficient to use the electric space heater. It will be close to 100% efficient, and all the heat will get delivered where it's needed. So there will be reduced heat loss from the rest of the house. Fossil-gas furnaces tend to be inefficient (it could be in the range 60-80%, though a modern modulating condensing one could get up to 90%).

In terms of cost-efficiency, there's a good chance that using fossil-gas will be cheaper. Particularly if the electricity network you are on uses fossil-gas to generate electricity.

In terms of resource-efficiency and sustainability, the better option will depend on your electricity contract and supplier. If your buying of more electricity increases investment in renewables, or if your supplier is already 100% renewables, then the electric heater is definitely better. If your electricity supplier burns fossil gas, then both options are problematic, and the balance will depend on all the combined inefficiencies in each system: a CCGT gas plant will throw away 50% of the energy from the gas, and the transmission and distribution system might throw away another 5%. Your furnace might throw away 15-40%, and the internal losses within your house might be another 10-40%. If your electricity supplier burns coal, then the gas furnace will be better than the electric space heater.

Ultimately, the best resource efficiency will almost certainly come from properly insulating and ventilating the property so that very little artificial heating is needed in winter, and very little artificial cooling is needed in summer. The EnerPHit standard and accompanying guides are probably the best way to go about that.

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EnergyNumbers has a good answer (+1), but why don't you measure it and let us know?

Of course "efficiency" is a little ambiguous. Green house gas production? Just your $$? The latter is easier, the former changes over time.

Get one of those power meters for the plug and see what it uses overnight. Most space heaters are ~1500 W, which is a lot. Your power bill has the rate and distribution costs.

The natural gas for the furnace is a little tougher. But you should have a monthly history. You can see when you turned your furnace on for the winter. If you have other gas appliances, then subtract the previous month and call the rest your furnace. E.g. turn on furnace in October, so subtract what you used in September and call the rest your furnace use. Take your winter monthly bill, subtract this base-use, divide by 30 (days/month) and that gives your daily cost of your furnace. You probably turn your heat down at night for sleep but also while your out during the day. It might balance out so call it 1/3rd at night (8 of 24 hours). (Maybe it's 6 hours of sleeping (1/4th), but with the furnace down you use it less, but it's colder at night - it probably all washes out).

So 1/3rd (or 1/4th) of 1/30th of your monthly winter gas bill (minus base use) vs. average (multiple measurements, please :) of 1 night of powering a space heater.

Again, if you're measuring $$, don't forget distribution charges, etc.

Normally I'd just say turn the furnace down and use a heavier blanket with thicker pyjamas and call it a day. But old houses can be leaky, and they leak faster when they're warmer (rate of heat transfer is directly proportionate to the difference in temperature). I have an old house and until I finish renovations, it's leaking heat in the winter. But you can seal windows in the winter (plastic cover) for rooms you don't use, etc. Plus I notice my furnace goes on more if I turn my furnace fan off at night because all the heat migrates upstairs and thermostat is on the main floor; it's more efficient to leave the fan on.

Mostly I want you to measure it and let us know. :)

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