Electric heater efficiency - Before anyone asks ;)

amtrakuk

I'm surprised I haven't seen anyone ask which electric heater is more efficient yet...

To save time just like to remind everyone ALL types of electric heaters are equally efficient. No matter what the ads or websites say.

A favourite of mine is Cadrew's comparison of a 1kW brand new fancy £300 electric radiator gives the same amount of heat as your granny's antique 1kW bar fire.

For every 1kW (1 unit) of electricity used you get just under 3,500 BTU no matter if its a convector heater, radiator, halogen heater, infra red heater.

If a heater says it is more efficient then it's not using the electricity > not generating heat - simple as.

Cardew

amtrakuk wrote: »

A favourite of mine is Cadrew's comparison of a 1kW brand new fancy £300 electric radiator gives the same amount of heat as your granny's antique 1kW bar fire.

Not only a £300 electric heater, but there have been posts on MSE of a single heater costing as much as £1,800.


Other points:


1. If an electric heater is filled with some 'magic' substance such that it retains the heat after power is switched off, then it will be slower to warm up. The sum total of heat produced, for the same running cost, is exactly the same. That also applies if the heater has a fan, or emits light.


2. That applies also to Infra Red heaters.


3. Whilst a heat pump can produce two or three times as much heat for a single unit of electricity, it is not strictly a heater. It is a device for extracting heat from outside the property and transferring to the interior.

amtrakuk

Cardew wrote: »

Not only a £300 electric heater, but there have been posts on MSE of a single heater costing as much as £1,800.


Other points:


1. If an electric heater is filled with some 'magic' substance such that it retains the heat after power is switched off, then it will be slower to warm up. The sum total of heat produced, for the same running cost, is exactly the same. That also applies if the heater has a fan, or emits light.


2. That applies also to Infra Red heaters.


3. Whilst a heat pump can produce two or three times as much heat for a single unit of electricity, it is not strictly a heater. It is a device for extracting heat from outside the property and transferring to the interior.

Regarding heat pumps. I heard the efficiency starts falling rapidly below 5c and are not much use at 0c

lstar337

The only time it acceptable to pay more for an electric heater, would be if you are installing them as a fixed heating system and you want something pretty on your wall.

lstar337

amtrakuk wrote: »

Regarding heat pumps. I heard the efficiency starts falling rapidly below 5c and are not much use at 0c

Depends on the specification of the individual units.

Their efficiency will get closer to 1:1 as temperature drops.

That being said, we have some old Mitsubishi CityMulti units here at work, and they still give out a good amount of heat when it has been below zero outside, so they don't seem to stop producing heat.

Newer units we have are much more efficient.

amtrakuk

lstar337 wrote: »

The only time it acceptable to pay more for an electric heater, would be if you are installing them as a fixed heating system and you want something pretty on your wall.

That's very true... when I moved from Gas to electric I went to Argos and started with a load of cheap wall mountable convector heaters. I think they were about £15 each. They may not have been as pretty as a £300 oil filed designer radiators but they were as efficient at heating the room.

amtrakuk

lstar337 wrote: »

Depends on the specification of the individual units.

Their efficiency will get closer to 1:1 as temperature drops.

That being said, we have some old Mitsubishi CityMulti units here at work, and they still give out a good amount of heat when it has been below zero outside, so they don't seem to stop producing heat.

Newer units we have are much more efficient.

As far as I'm aware the bigger commercial types generally combine an auxiliary heat source (gas or electric) once the temp drops to keep the circuit from freezing up

polymaff

amtrakuk wrote: »

I'm surprised I haven't seen anyone ask which electric heater is more efficient yet...

To save time just like to remind everyone ALL types of electric heaters are equally efficient. No matter what the ads or websites say.

A favourite of mine is Cadrew's comparison of a 1kW brand new fancy £300 electric radiator gives the same amount of heat as your granny's antique 1kW bar fire.

For every 1kW (1 unit) of electricity used you get just under 3,500 BTU no matter if its a convector heater, radiator, halogen heater, infra red heater.

If a heater says it is more efficient then it's not using the electricity > not generating heat - simple as.

As Professor Joad used to say, "It depends what you mean by ..."

You are assuming that efficiency is the energy liberated versus the electrical energy supplied.

The purpose of your granny's heater is to provide comfort - not to liberate energy. Looked at less superficially, therefore, different heaters provide varying levels of comfort per kWh.

Now, who used to say "A little knowledge is a dangerous thing?"

Oh, that was me. :)

amtrakuk

polymaff wrote: »

As Professor Joad used to say, "It depends what you mean by ..."

You are assuming that efficiency is the energy liberated versus the electrical energy supplied.

The purpose of your granny's heater is to provide comfort - not to liberate energy. Looked at less superficially, therefore, different heaters provide varying levels of comfort per kWh.

Now, who used to say "A little knowledge is a dangerous thing?"

Oh, that was me. :)

Ahh yes the comfort factor... Yes that applies when you take dear aunt Mary... I told her not to sit in front of her 1kW electric fire for too long as she wont feel the benefit when she goes to sit across the room by the standard lamp to do her sewing...

This scenario is true of all "spot heating". You'll roast in front of it and freeze when you move away. Spot heating which includes halogen heaters, infra red heaters etc work by heating objects first then the air. Where heating based on convection (Convector heaters, Radiators etc) heat the air first, Taking the chill off the room, which in turn heat objects.

It also depends on the application, there is little point in using an electric radiator if you're only going to be in a room (eg bathroom) for a few minutes as you'd have finished "brushing your teeth" by the time the heater has heated up and started to work. Therefore a suitable "spot heater" eg, infra red bar heater would be more appropriate. On the flip side an infra red bar heater will not be appropriate in the front room as the example above, it will heat the objects first and only when their temperature is greater than the surrounding air will they start to warm the air in the room and "take the chill off". In this situation a convection or radiator would be more appropriate as they heat the air first - Taking the chill off, then heat objects.

Either way a 1kW spot heater OR a 1kW Radiant bar heater will still consume the same amount of electricity per hour.

amtrakuk

Just come across this youtube video with a good explaination as to why heat pumps aren't that good in very cold weather;

https://www.youtube.com/watch?v=sgBWCGUUH_U

Andy_WSM

amtrakuk wrote: »

Regarding heat pumps. I heard the efficiency starts falling rapidly below 5c and are not much use at 0c

That's outdated info as technology has moved on somewhat.

I've just had a new air to water pump fitted and it's rated to operate to -15C and below using the latest refrigerant gases. At temperatures much lower than this the COP makes heating with a heat pump no more efficient than that 1 bar fire referred to above; however, in the South West a frost is rare and anything as cold as -10C has people thinking the world is about to end.