Efficiency equals the time heater is on minus the time it takes to warm the room to a level where room can be used.
So if it takes an hour to warm room and room is used for an hour then efficiency equals 50% but same room used for 3 hours and efficiency equals 75% with the same heater.
So in a room heated 24/7 efficiency equals 100%.
There are three forms of electric heating. The heat pump is cheapest to run as it actually just transfers heat from outside to inside but expensive so I will forget those.
Next is the radiant heater. These don't heat the air they heat objects in their path just like the sun does. So as soon as you switch them on you feel the heat even with all windows open they still work. Often used in garages where all air lost every time door is opened also were popular at one time in bathrooms. The draw back is control they are on or off and so on their own rather useless in the home as can't use any thermostatic control. Thermostats measure air temperature and radiant heaters don't heat the air they heat people direct.
So next is the fan heater. They heat the air very fast no warm up time and also not cool down time so 5 minutes may be enough to start using the room. Down side is noise and also switching off you start to feel the cold again very quickly.
The worst heaters are storage types be it under floor or as radiators these can take hours to both warm up and cool down so end up heating empty rooms.
So it's all down to heat up times really. Panel heaters tend to heat up quicker than oil filled radiators but now we get to the hard bit. In a bedroom OK we may want it to cool down slowly so we go to bed room at 20 degs then heater turns off and room cools slowly to 16 degs then before we raise it switches on again and heats room back to 20 degs. There are two basic ways to do this. One is a duel level thermostat set to both temperatures the other is something which stores the heat reducing cool down speed.
So to me the oil filled radiator cool down time means you switch on half hour before required then off when you are about to get into bed and it stays warm long enough for you to fall asleep before it cools down. But the panel gains by switch on only 20 minutes before going to bed but losses as cools down too quick so requires some special switching arrangement to reduce the ramp down speed.
The best cheap way is to combine both convected and radiant heat. The radiant heater means heater switched on as you enter room no warm up time required. As convector heater warms up the air radiant heater turns off and then convector heat is set to lower over night temperature.
So it is a balance between efficiency and control also speed of getting into bed. And the temperatures required.
Once running and up to temperature it does not matter which heater you use 1kW in = 1kW out (except for heat pumps) it's only the heat up and cool down time which alters efficiency does it run for 1 hour before room is used or 20 minutes before room is used or 2 minutes (latter is radiant heater).
Do remember tungsten bulbs give off radiant heat. Since you undress in the light then once in bed you turn off the light you can use tungsten bulbs to save energy during winter months. Simply swap LED to tungsten in winter and back to LED in the summer and the size of air heater required is reduced. Clearly government officials never went to school and learnt about radiant heat or they would have not got rid of tungsten bulbs!
Thank-you Eric, what an amazing reply that was, very educational.
I should have explained in my first post that I do not like heaters on when I am in bed as I warm up very quickly and even use a summer duvet in the Winter.
I just want to be able to set the heater to come on for 1 hour twice a day (maybe 9a.m and 4p.m) as the bedroom is at the back shady part of the bungalow.
I do have mould developing on my new furniture, pine wardrobe, bedside cabinet and inside the divan bed drawers. I know heating the room will not stop that as it is Summer and I have the windows open all day every day and the white furry mould still re appears but I think it would be a good idea to warm the room daily in the Winter months.
Regarding the mould I have read a few articles and no longer dry my washing inside the property, I open the bathroom window when showering and kitchen window when cooking.
On another forum there was a huge argument over heater efficiency some manufacturer had claimed there heater was more efficient than competitors and the comment was 1kW in = 1kW out for all but heat pumps which is of course true.
The old radiant heater used often on the bathroom wall must be about the best for instant heat. There is little need to switch on before entering to room.
However one point often missed if aimed at a window even if double or triple glassed the heat will go out of the window. Also any item between you and the heater will stop the radiated heat.
The major problem is the thermostat as the thermostat measures air temperature and radiant heaters don't heat the air.
However it would seem these would be best for your life style. What is needed is a number of small heaters as switching on and off does not work do you remember the old radiant fire with four bars you controlled heat using one, two, three or four bars not switching on and off.
Today we seem to get heat lamps rather than bar heaters often around the 150W each. Often classified as medical having say 6 lamps with switches for each would in theroy give you 6 levels of instant heat.
However it is what they look like. A discreet panel heater looks far better than 6 lamps hanging from the ceiling even if those 6 lamps do a better job.
In theroy fitting heat lamps uses less power, in practice I will use gas central heating as gas is cheaper than electric and although the one Myson blow heater does a better job than the radiators (which don't radiate heat they use convection) the radiators have a buffer effect so one is unaware when central heating is one or off so in real terms the radiator works better.
I measure the humidity outside and inside and convert to dew point. Although the humidity may be lower in the house the dew is rarely lower than outside. Heart of Winter dew point may drop as low as 7 degs C and in Summer raise to 15 degs C 16 is highest recorded in my house outside August can exceed that but rare.
Point is any body of air will vary in relative humidity according to temperature but the dew point will remain the same. Some plants can absorb moisture from air (not sure if mould is plant or animal) but most need the humidity to be quite high to do that. My house is between 31% heart of winter to 55% hight of summer. Yet mould seems to come during the winter in bathroom I will assume because the wall is cold. Summer in spite of higher humidity we have less of a problem.
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