Should I replace electric heater with a/c unit in bedroom?

[MoonMan2]

Am thinking about getting an a/c unit installed in bedroom. My bedroom is about 27m3. I currently heat it at night using a 1kW electric convector heater. I am happy when the temperature is around 17 degrees, so the heater doesn't need to work that hard. It clicks on and off during the night stopping the temperature dropping below 17 degrees.

I am trying to work out if there will be a substantial saving in using an a/c unit as a heater. The unit I am thinking of getting says the following on the spec:

STARTING CURRENT: 3.5A
SYSTEM RUNNING CURRENT (A) Heating/Cooling [MAX] 3.5/2.9 [7.3]

Any thoughts?

Also what does the 7.3A max mean?

 

[winston1]

To make a substantial saying don't use a heater and get some thicker bed coverings.

 

[JohnW2]

Am thinking about getting an a/c unit installed in bedroom. My bedroom is about 27m3. I currently heat it at night using a 1kW electric convector heater. I am happy when the temperature is around 17 degrees, so the heater doesn't need to work that hard. It clicks on and off during the night stopping the temperature dropping below 17 degrees. ... I am trying to work out if there will be a substantial saving in using an a/c unit as a heater.

It really didn't ought to make much difference. If you need a certain amount of electrical energy to stop the temperature dropping below 17°, then you need that certain amount of electrical energy to stop the temperature dropping below 17° - whether that electrical energy is converted into heat in a convector heater or an AC unit. It sounds as if the heater in the AC unit you're considering is about 0.8kW, so it would probably have to 'click on' a little more than your 1kW heater does.

Kind Regards, John

 

[ekmdgrf]

As JohnW2 says, there is a given amount of energy needed to raise the temperature in the room, so it doesn't really matter how that energy is used. Of course, when comparing different systems, there is a question of efficiency, however this is usually a case of stopping the energy that you put in getting wasted as heat. For some reason, when dealing with heaters, this problem seems to disappear.

 

[DetlefSchmitz]

As JohnW2 says, there is a given amount of energy needed to raise the temperature in the room,

Unless of course, you use a heat pump...

 

[DaftPunk]

Inverter air con units are upto 600% efficient when used for heating so should be cheaper to run than a convector heater.

 

[JohnW2]

As JohnW2 says, there is a given amount of energy needed to raise the temperature in the room,

Unless of course, you use a heat pump...

Ironically, what ekmdgrf (slightly incorrectly) cited me as having said remains true even with a heat pump, although what I actually wrote ("... amount of electrical energy ...") doesn't ... the amount of energy needed to heat a room to a given extent will obviously always be the same, but that energy does not necessarily all have to come from the supplied electricity - it may be transferred ('pumped') into the room from elsewhere.

However, this does make me wonder whether we are being a bit quick in 'dismissing' the OP's idea, without knowing much about what sort of AC unit he is considering. If it is such that it can act as an efficient heat pump when heating, then it will, of course, result in more energy entering the room than the amount of electrical energy it consumes (i.e. an 'efficiency' ">100%"). I was under the impression that cheap domestic AC units (which I had dangerously assumed was probably what the OP was talking about) were not at all good at this (being essentially just intended for cooling), but I may well be wrong.

Kind Regards, John

 

[JohnW2]

Inverter air con units are upto 600% efficient when used for heating so should be cheaper to run than a convector heater.

Yes ... please see what I've just written to Detlef. If the AC unit we're talking about is capable of 'reversing' and acting as an efficient heat pump, then it obviously could result in a cost saving. However, as I've just written, I thought (probably wrongly!) that 'cheap' domestic AC units were essentially designed for cooling, and either couldn't heat at all, or weren't very efficient at it. [Indeed, there at least used to even be some that used blown resistive heating to heat - hence 'fan heaters'!]

600% sounds (to me!) very high for any sort of heat pump, so maybe I'm out-of-touch with advances in the technology. As for 'inverter' AC, my understanding is that refers simply to having a variable speed (rather than fixed-speed on-off) compressor, hence much better control of temperature, which I would have thought would only result in a fairly modest improvements in efficiency - but maybe I'm again wrong!

If heating efficiencies anything like 600% are now easily attainable with AC units, and given the cost of fuel/electricity, why aren't we all using it?

Kind Regards, John

 

[Lectrician]

Air con will likely be noisier, and can dry the air out too much, giving you outh ulcers. They are not particularly recommended for bedrooms.

 

[DetlefSchmitz]

If heating efficiencies anything like 600% are now easily attainable with AC units, and given the cost of fuel/electricity, why aren't we all using it?

From what I've heard ASHPs are more likely to have an efficiency between 200 and 400% and towards the lower value when you really need it.

Nevertheless if you only have access to electricity, it is a real saving.

At the risk of waking up some of the dinosaurs here I offer the following link for your consideration.

https://www.gov.uk/government/polic...supporting-pages/renewable-heat-incentive-rhi

...stands back...

 

[JohnW2]

From what I've heard ASHPs are more likely to have an efficiency between 200 and 400% and towards the lower value when you really need it.

That's much more like what I thought. As I wrote:

600% sounds (to me!) very high for any sort of heat pump, so maybe I'm out-of-touch with advances in the technology.

However, the question remains in my mind to as to whether 'cheap' UK aircon units (as opposed to things actually called, and sold as, ASHPs) actually do act as useful heat pumps (at all, or at reasonable efficiency) when heating (i.e. moving heat into the building)? As I wrote, I was under the impression was that such was generally not the case.

Kind Regards, John

 

[ekmdgrf]

If heating efficiencies anything like 600% are now easily attainable with AC units, and given the cost of fuel/electricity, why aren't we all using it?

I had a fleeting look at getting a heat pump. From memory, I seem to recall:

Ground Source Heat Pumps tend to be better for heating (maybe that's where you get the 600% efficiency) but the capital investment is quite massive (around 15k) and involves demolishing your garden (or indeed having one to demolish).

I looked at getting air con in three rooms and was quoted 4 grand. Another not insignificant expenditure.

The other problem is that they tend to provide only a small amount of heat. This works in modern, well-insulated houses, when you can heat the house slowly and retain it but isn't so good for 1930s solid brick places like my own, where the heat escapes about as fast the boiler can put it in. It does have the disadvantage that like storage heaters, you need to plan your heating in advance.

Disclaimer: I'm not an expert on heating

 

[davelx]

From what I've heard ASHPs are more likely to have an efficiency between 200 and 400% and towards the lower value when you really need it.

That's much more like what I thought. As I wrote:

600% sounds (to me!) very high for any sort of heat pump, so maybe I'm out-of-touch with advances in the technology.

However, the question remains in my mind to as to whether 'cheap' UK aircon units (as opposed to things actually called, and sold as, ASHPs) actually do act as useful heat pumps (at all, or at reasonable efficiency) when heating (i.e. moving heat into the building)? As I wrote, I was under the impression was that such was generally not the case.

Kind Regards, John

I've had a delonghi CP30 inverter aircon unit in my living room for several years and it heat the 26' x 11' room very well in the evenings in the current weather (outside temp 6-10C) when I don't want the central heating running.

heat input to the room is rated at 3.5kW with electrical input of 1050W, which gives efficiency of 333%, at external temp of 7C and internal temp of 20C.

 

[JohnW2]

I've had a delonghi CP30 inverter aircon unit in my living room for several years and it heat the 26' x 11' room very well in the evenings in the current weather (outside temp 6-10C) when I don't want the central heating running.

Fair enough.

heat input to the room is rated at 3.5kW with electrical input of 1050W, which gives efficiency of 333%, at external temp of 7C and internal temp of 20C.

Have you any idea as to whether it actually achieves that (or anything like it) - or are you merely quoting the manufacturer's claims?

I wonder how the cost of 3.5 kW's worth of, say, gas heating compares with the cost of 1.050 kW of electricity? As others have suggested, heat pumping probably becomes a potentially attractive option if/when electricity is the only able form of energy.

Kind Regards, John

 

[davelx]

Have you any idea as to whether it actually achieves that (or anything like it) - or are you merely quoting the manufacturer's claims?

I wonder how the cost of 3.5 kW's worth of, say, gas heating compares with the cost of 1.050 kW of electricity? As others have suggested, heat pumping probably becomes a potentially attractive option if/when electricity is the only able form of energy.

Kind Regards, John

Those are the ratings from the installation manual. I haven't measured the efficiency - to do that I'd need an accurate value for the rate of heat loss from the room per degree temp difference inside to out, which I don't have. However, even if I only want to heat that one room (which at this time of year is the case), if I use the central heating I have heat loss from all the piping in the house even if all the rads except those in the living room are turned off. The pipes in the first floor are not insulated, so I am heating the floorspace and thus, to some extent, the other rooms too.

I guess one way I could do a comparison is to measure the gas usage for one evening, and then compare it to the electricity usage (I have plug-in meter and the aircon runs on a 13A socket) on another evening with similar outside temperature and wind conditions.