ruben3 ruben3 posted February 18th, 2014 at 7:17 pm to Other. Viewed 383 times. Answered 8 times.

i live in a small room, probably around 20m2. which is more efficient at achieving a standard level of comfort? a halogen space heater (or coiled one), a reverse cycle heat pump a/c unit, or a fan heater?

i guess any given level of comfort is pretty subjective, but just wanted your thoughts.

Last answered by WDgreen about 70 months ago.

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Grant wrote on February 18th, 2014 at 11:20 pm
Grant (elite user)


A radiant fan heater. The cost outlay for a reverse cycle A/C unit is ridiculous unless you will also use it for cooling. The glow from the heater is pretty Disco but they work very well. The efficiency of the A/C unit is a bit of a fake. Especially for small spaces.


amabush wrote on February 19th, 2014 at 9:33 am

How about running costs? If the Sea Otter is curled up in his little room with a choice between the above methods, which provides best value for heating?

mattnnz wrote on February 19th, 2014 at 1:39 pm

A halogen heater won't do the job. A oil-filled space heater is the thing. They sell them at pico-mall. A reverse cycle AC cannot be as energy efficient because it has to run both the compressor as well as the blower motor. The compressor+motor is not 100% efficient at converting electricity to work to move heat energy from outside to inside your room. An electric heater more efficient because all the energy it uses turns to heat. If all you want is to make the room warm, my money is on the reverse cycle AC. It will cost you however.

Grant wrote on February 19th, 2014 at 5:07 pm
Grant (elite user)


Heaters (not reverse cycle) all convert the electricity they consume to heat and none are more efficient at than another. 1kW of power will be converted to heat. More power, more heat. If you add a fan to help circulation there is additional power consumed. Radiant heaters are better at heating large spaces by heating the surfaces (and you) rather than the air so much. Space heaters are nice but a 1kW unit converts the same amount of power to heat as 1kW radiant heater, halogen heater or any other resistive heater and all give the same heat output for the power in. If a fan heater is rated at 1kW it doesn't convert all the energy to heat as some power is driving the fan so it will give you less than 1kW's worth of heat output.

Heat pumps (reverse cycle air con) are the most efficient heat sources as you get more energy in the form of heat than for the electrical power input. A 1kW heat pump will give you more than 1kW's worth of heat and that is the cost saving. You will still be paying for 1kW of power though but you'll be hotter. If the outside temp is around 10ºC a heat pump can be more efficient than a resistive heater by a factor of 3 to 4 times.

To heat that space nicely you'd need about a 1.5kW heater but could get away with a smaller AC unit for the same heating result.


amabush wrote on February 19th, 2014 at 5:52 pm

Useful stuff, thanks to both.

mattnnz wrote on February 19th, 2014 at 9:08 pm

I stand corrected. :) I wasnt thinking about it correctly.

Grant wrote on February 19th, 2014 at 11:44 pm
Grant (elite user)


You're welcome. Actually there is a very good NZ site regarding heaters. Saw it a long time ago but sure it's still there.

This explains the heat pump idea better than I can. Not all the comments are correct.

The Carnot engine they talk about leads to the Carnot Limit which under a certain outside ambient temp the efficiency is decreased to 1:1. Basically a crap heater. Somewhere around -18ºC or something. Beyond that they cannot heat. Unlikely here.

The best heater for a small space is one that gets the air circulating and not leaving you sitting on the heater to avoid the cold spots. If you don't want to lay awake all night with an orange glow in the room or feeling like your face is burning on one side then a radiant heater is not for you. An oil heater with a small fan is brilliant. Safe as, unless you sit on it for too long and get zebra arse stripes and it moves the air around. Not fast at heating but not obtrusive. If you don't clean it, it is unlikely to catch on fire. Pretty bulky though. A small fan heater, not radiant, works really fast but makes you feel really dry (no idea why that's just personal). Don't do the dodgy cheap Chinese models though as they have no safety features and eventually will either breakdown and stop (ok) or catch on fire (not so ok).

For the OP I'd go a small (low speed fan setting) quiet fan heater, good quality and check out it's safety features. Small investment. Works. Low on the floor and the draft will move upwards. For a bloke that is good news. Happy crutch draft is always a good thing, admit it.

Fee is in the Post.


WDgreen wrote on February 20th, 2014 at 6:19 am

I agree with the above information and would add to look into how your heat is being lost (windows,doors) and see if you can improve them. A few methods exist for inexpensively increasing the window resistivity as well but don't expect a good view.

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