Can anyone tell me how efficient electric devices (specifically incandescent lights and PCs) are at heating? If I heat my house with a central electric or portable electric heater, does it save anything to turn other devices off? It seems to me that I may as well leave them on, as it’s just going to help heat the place anyway.
Does that make any sense to anybody?
Makes perfect sense. Appliances that do not export energy from your house are 100% efficient at creating heat from electricity. Appliances that do, like HAM radio transmitters and clothes driers vented outside, convert 100% of whatever they don’t export into heat.
However, electricity is typically more expensive than some other heat sources (fair enough, because it’s perfectly clean and very versatile).
Heat pumps are more than 100% efficient, because they can actually make the outdoors colder.
Electric devices are 100% efficient of producing heat from energy, heat pumps can get greater then 100% (as they move heat instead of create it). So if you heat with resistance heat, turn on the plasma widescreen TV, all the IC lights you have, and whatever else floats your boat - it all goes to heat at 100% efficiency.
You have to consider all factors. If you are using IC bulbs and a electric space heater, you are using more power then using CF bulbs and a electric space heater, though you are getting more heat from the IC + heater setup, you may not need that heat (only if you run your spaceheater on constant on, if you set the thermostat the heater should cycle off and be the savings of the IC lamp’s heat contrubution), and if the light is placed on a ceiling fixture, a lot of that heat is lost through the ceiling, anyway - this could make matters worse if the heat from the fixture creates a upwards draft into a attic, pulling room air up and away… But if you have a bunch of IC and CF lights, and you want to get rid of the IC ones, use them in the heating season would be better then the cooling season.
Good reply Napier, but a point of contention:
It’s not really clean, but the ‘dirt’ and heat was just moved from your home to the power plant. Due to the laws of thermodynamics a power plant, operating perfectly can only manage perhaps 50% efficiency, the rest of the energy is lost to heat (though some of that heat can be used to heat the powerplant - called co-generation). So if your going to heat it would be generally better to just burn on site - which is pretty close to 100% efficiency if it is unvented, and perhaps 70-85% efficient if it is vented, far better then the best case 50% electric.
Incandescent lights, computers, printers, etc., do add heat to your home. If you’re operating your heating system via a thermostat, then those devices will add to the heat in your home, and will slightly reduce the amount of heat you need to provide from your heating system. If you’re heating via electric resistance, you’re close to a wash when it comes to efficiency. If you’re heating via a heat pump, which, as Napier pointed out, has >100% efficiency, then your light bulb is providing that extra bit of heat with a less efficient source. If you have other heating sources, the dollar value would depend upon the relative costs of the fuel and electricity, and the efficiency of your heater.
Where you would gain more benefit is in the summertime, when you’re running an air conditioner. The heat that your lighting and appliances kick out is a significant part of your cooling load. When our firm does HVAC renovations on buildings, one of the first things we suggest is to do a lighting renovation at the same time. If the building was using older generation, less effective lighting technologies, changing to new, more efficienty lighting systems can allow us to downsize the size of air conditioning system required. This decreases both the purchase cost and the operating costs for the AC equipment, which in turn generally pays for the lighting upgrade.
All the heat produced by an incandescent light is produced as efficiently as an electric resistance furnace or heater. The ‘waste’ electricity that is not converted to light becomes heat, which warms the room. That is good in winter, bad in summer.
However, this is, in practice, less efficient heating than your furnace provides.
Your furnace is designed to heat your home. It has fans & vents to distribute the heat where it’s wanted, and a thermostat to turn it on and off as needed. The heat from an incandescent light is produced whenever the light is on, even if the room is already at the desired temperature. Also, this heat is often not in the most optimal location – for example, heating the ceiling in the middle of the room does little to keep the occupants comfortable. Even from a reading lamp right over your shoulder, most of the heat will rise up, rather than warming you.
So while the heat from any electrical device is produced equally efficiently, a well-designed heating system is more efficient at warming a house. The efficiency in those other devices comes when you are able to make use of the heat they produce, that would otherwise be ‘waste’ heat.
Hmm. I guess I’ll stop feeling so bad for now that I can’t find CFL replacements for the spotlight fixtures in my overhead fan.
Thanks! 
Also, you should consider Total Cost of Ownership in the equation. If you have to replace your lightbulbs every year instead of every 3 years, then the amount you save in energy probably isnt worth the replacement costs.