# Hot/cold AC versus other heating



## Kikie (Nov 7, 2008)

Has anyone one got experience of the air-conditioners that switch from cold to hot? What are your thoughts if so re efficiency and cost compared to other systems like gas fired hot water radiators? 

We like a whole room to be heated, not just the few feet in front of a heat source. We were told by our landlady that their research showed the gas tank fired hot water radiators to be the most efficient but an agent (yes I know but she seemed nice, wasnt doing a pushy sell  ) has told us the electricity for the hot/cold AC is cheaper.


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## Michael Kelly (May 30, 2017)

I have hot AC (mitsubishi, installed in 2006) and never use it as it is useless! AC is good for cold only.


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## Rabbitcat (Aug 31, 2014)

I have ducted air con and it is excellent for both hot/cold


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## stevesainty (Jan 7, 2011)

Michael Kelly said:


> I have hot AC (mitsubishi, installed in 2006) and never use it as it is useless! AC is good for cold only.


A most AC units are mounted near the ceiling you need to get the hot air to travel downwards otherwise it will appear useless. 

You achieve this by switching your ceiling fan to the winter setting, normally this means the fan travels in a clockwise direction, using the toggle switch on the side of the fan.

Hot air will then be pushed down into the room and this circulation will push the cooler air, on the periphery, upwards to be heated again by the AC unit.

Don't forget to turn your fan back to summer setting, anticlockwise, before you need it in the summer.

Most inverters are quite efficient in heating mode, I don´t understand the physics though, as you get something like 3kw heating out for only 1kw power in.


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## snikpoh (Nov 19, 2007)

Michael Kelly said:


> I have hot AC (mitsubishi, installed in 2006) and never use it as it is useless! AC is good for cold only.


You obviously have a faulty unit.


A/c is the most cost-effective electrical heating/cooling - fact, pure physics.


We have modern panasonic inverters which are brilliant for both hot and cold - and extremely cost effective to run. However, the point about using a fan as well is a good point.


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## xgarb (May 6, 2011)

We have one that cools, heats or dehumidifies. It works really well. You can control the angle the air comes out.

Didn't notice an increase in the bill last winter but it wasn't used a lot.

I think this is one area where you get what you pay for and it might be worth getting a few opinions on installation and models.


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## 95995 (May 16, 2010)

snikpoh said:


> You obviously have a faulty unit.
> 
> 
> A/c is the most cost-effective electrical heating/cooling - fact, pure physics.
> ...


Yes, the fan is a good point, BUT modern reverse cycle air conditioners (i.e. those that heat and cool) automatically switch the blades to send the heat down when turned to heating. That's what I used in Australia and it was amazingly effective. It's also what I would go for, as the temp is very adjustable and when you turn it off it immediately stops heating - which is handy. The cost to run, of course, depends on how warm or cool you prefer your room/s.


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## Pazcat (Mar 24, 2010)

Our unit works very well in a large room both in summer or winter but having said that we had a log burner installed and used that all winter instead.
Nothing beats real good radiating heat.

Not bothered to do a cost comparison so no help there.


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## chrisnation (Mar 2, 2009)

stevesainty said:


> A most AC units are mounted near the ceiling you need to get the hot air to travel downwards otherwise it will appear useless.
> 
> You achieve this by switching your ceiling fan to the winter setting, normally this means the fan travels in a clockwise direction, using the toggle switch on the side of the fan.
> 
> ...


I like most of this post. The last sentence is a bit suspect tho'. 1kW in - max 1kW out. In fact less, because of losses in the system. For a start, some juice is used to run the machinery, not to generate hot air.

But I did go for reversible fans, for the reason given, and found that Brico Mart sells (sold me) Mitsi units at not much more than unknown Chinese brands and several €100s cheaper than the same Tosh kit.


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## trotter58 (Feb 8, 2017)

chrisnation said:


> I like most of this post. The last sentence is a bit suspect tho'. 1kW in - max 1kW out. In fact less, because of losses in the system. For a start, some juice is used to run the machinery, not to generate hot air.
> 
> But I did go for reversible fans, for the reason given, and found that Brico Mart sells (sold me) Mitsi units at not much more than unknown Chinese brands and several €100s cheaper than the same Tosh kit.


I know it sounds suspect but stevesainty is right "_Most inverters are quite efficient in heating mode, I don´t understand the physics though, as you get something like 3kw heating out for only 1kw power in_."

See https://en.wikipedia.org/wiki/Air_conditioning ...*seasonal energy efficiency ratio* for an explanation.
......"From equation (2) above, a SEER of 13 is equivalent to a COP of 3.43, which means that 3.43 units of heat energy are pumped per unit of work energy."


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## chrisnation (Mar 2, 2009)

trotter58 said:


> I know it sounds suspect but stevesainty is right "_Most inverters are quite efficient in heating mode, I don´t understand the physics though, as you get something like 3kw heating out for only 1kw power in_."
> 
> See https://en.wikipedia.org/wiki/Air_conditioning ...*seasonal energy efficiency ratio* for an explanation.
> ......"From equation (2) above, a SEER of 13 is equivalent to a COP of 3.43, which means that 3.43 units of heat energy are pumped per unit of work energy."



Is there a thermodynamisist in the room? What is a "unit of work energy". What are "units of heat energy" ? 

If this had been expressed in joules or BTUs I'd understand it but unless it is implying that whatever the units - joules/BTUs/pint mugs - you get 3.43 of one per 1 of the other, I still don't get it. It still looks like sumfink 4 nuffink.


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## trotter58 (Feb 8, 2017)

chrisnation said:


> Is there a thermodynamisist in the room? What is a "unit of work energy". What are "units of heat energy" ?
> 
> If this had been expressed in joules or BTUs I'd understand it but unless it is implying that whatever the units - joules/BTUs/pint mugs - you get 3.43 of one per 1 of the other, I still don't get it. It still looks like sumfink 4 nuffink.


A simpler explanation here Heat Pumps: How Can an Air Conditioner Be a Heater?
in the example given:
The resistance heater uses 1.5 KW to produce 5120 BTUs
The AC (heat pump) uses 1 kw to produce 10,000 BTUs
For the same electrical input (KW) the heat pump will produce approx 3 times the BTUs (heat) of the electric resistance heater.
However, it should be noted that the efficiency of the AC as a heat pump is dependent on the outside temperature.


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## Blanco53 (Mar 6, 2017)

I agree that the hot / cold air con units are very efficient.....if rather dull.

Now when it's blowing out cold air (as it is now) the aesthetic quality of the unit isn't that vital. However, for those chilly winters evenings, the glow from my log burner makes me feel snug and warm, even if the hot air unit is, in all probability, more efficient!


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