Underfloor Electric Heating

[Richard C]

I am currently having problems with a conservatory company regarding the size of the electric under floor heating system they have installed. The Edwardian style conservatory has a floor area of just under 20 sq/m & the size of the heater mat they installed is 2.5Kw. Knowing a little about heat loss calculations for conventional household central heating systems, I queried if this was sufficient to provide the primary heat source & both they & the manufacturer stated it was.

With an outside air temperature of 10 degrees & without the influence heat migrating from the house or the sun, the temperature struggles up to around 18 degrees; if the outside temperature drops to 0 it will only hover around 14 degrees & sometimes drops even lower.

A representative of the heater manufacturer has checked the system & reported no faults but would not get drawn on the question of insufficient capacity. I have since been told by another supplier that he usually allows 0.2Kw per sq/m, which obviously makes the size of my heater look seriously deficient. I have a meeting with the installer & am not sure what stance they are going to take. I would appreciate any information regarding the calculation of electric under floor heating requirements as a primary heat source in conservatories?

 

[Steve]

Whilst not knowing any calculations for UFH, I would have them install at least 5kw of heat. Though they may have just put 2.5kw in because its cheaper - they dont need to run a seperate circuit for this, they would have to go back to the consumer unit for the 5kw.

What you could do is to leave the UFH as it is, have that on for background heat, and top up with an air conditioner heat pump, which can also be used in summer to cool the place down. Those heat pumps do kick out a lot of heat and are a lot more efficient than UFH.

UFH is probably 50% efficient, maybe less (a lot of heat escapes into the earth, and a lot of energy used heating thermal mass of concrete), whereas air con heating is 200% efficient (refrigerant cycle drags heat energy in from outside, there aren't any electric heating elements anywhere)

I wish we had both, because whilst our heat pump heats the air, the tiled floor always feels chilly.

 

[Richard C]

See I got the forum then!

Crafty
Thanks for the response. I particularly didn’t want radiators so the floor slab is well insulated with UFH in mind; the supposed theory being that this reflects heat upwards rather than being absorbed by mother earth! As a new 12 way consumer unit was also being installed, I insisted that they wired the UFH to a dedicated circuit breaker on the new CU.

They company concerned did a lot of other work for me & are actually quite customer focussed - must be a rarity in this day & age! I suspect they will hold their hands up & look for the most cost effective compromise that will avoid them having to rip the floor up & start again. But I want to be sure of my ground just in case; hence the request for info.

If they do hold their hands up I would not be unreasonable, providing we can agree a solution that would give me the most benefit! Assuming they will do their best to avoid ripping the floor up, I am trying to go, pre-armed with facts & a good understanding of options that they may come up with i.e. backing up the UFH with either radiators plumbed into the house heating system or installing electric, ceramic/infra red radiators etc. I did not research conservatory heating/cooling the options in any detail & this is my first conservatory so I don’t have the benefit of previous experience. Interestingly, I had not considered the benefits of an AHU heat pump unit; do you think this would be worth going for? Presumably it would provide sufficient heat? &, as you say, it would also give me the benefit of AC in the summer! If I do go this route, can you advise what size unit I should aim for?

Thanks

 

[Steve]

Our air con unit is 9000BTU (the smallest DIY install kit B&Q did in summer 05). Think we got it with 20% off, cost about £350-400 at the time. However, our conservatory is only 9m². Ideally you need a 20,000BTU model, which for DIY might set you back £500-800, but professionally installed unit may be £1500-2000 (guessing there). Dont forget you have to have a length of pipework connecting the 2 sides of the unit together, unless you have a thru-the-wall system.

We have a professionally installed one at work, in the office, and it is whisper quiet, yet it brings me out in a sweat when i stand under it! The b&q ones are budget quality, a bit louder, more basic.

Then again, you can get an electric fan heater for £20 but it will cost more to run.

Radiators will place additional load on your boiler, may not be the best idea. Will also make the heating system take longer to warm up in winter, due to colder water passing through the boiler.

Our conservatory floor was insulated too, but its still freezing to walk on, and a heck of a lot of thermal mass to heat!

Its all up to you (and the conservatory company!)

I am a big fan of heat pump systems, as they are much more efficient at producing heat (200% efficient, for every kw they consume, they give out 2kw), but they are the most expensive to purchase and install, and maintenance can be expensive (a lot to go wrong).

 

[Richard C]

Crafty

Thanks for the ACU info, it's an advantage to be aware of all the options! I seem to remember that when I did the calcs for my first 2 bed, end of terrace many years ago, I needed a total capacity of around 38, 000 BTU; I know heat loss through a conservatory is probably astronomical (hence the request for info) but 20,000 BTU for a conservatory A/C unit seems rather a lot! Is that a guestimation, based on experience or is it calculated?

Just like to reiterate that if anyone else out can oblige with more info on the sizing under floor heating systems for conservatories, it would be a great help to me to be able to my meeting with the supplier next week armed with some facts.

 

[Steve]

ok, copied from air conditioner info at b&q website

Cooling capacity: 17000 BTU (4500w)
Ideal to cool a room up to 48m sq approx (shaded room typically north/east facing)
Ideal to cool a room up to 30m sq approx (bright sunny room typically south/west facing)
For conservatories reduce the above figures by 50 per cent as a guide only

Seems they have taken off most of their air conditioners for the winter, visit here for the current range. (those are the ones that require professional installation, not the DIY type, not that they are any better quality, they probably just dont have the quick connect coupling). Search google for air conditioning (uk sites)

 

[Richard C]

Crafty
Thanks again for the info & the links; I looked at the B&Q A/C stuff on offer at our local mega store last year but I opted for a professional conservatory package in order ‘to save me time’!! & allow me to concentrate on the rest of the rebuilding work needed on this 1960’s, disaster of a house I’ve bought so it didn’t seem relevant at the time. I think my moto for 2006 will be ‘if you want it done properly, do it yourself’; or at least take total control of it!