under floor heating

[Boabie]

I need to replace my warm air heating and carpeting. I am thinking of using a quantity of copper pipe (better heat transfer than plastic) around the outer edge of the room under porcelain floor tiles. Can any one tell me how to calculate the length of pipe required to equate to 1800w or 6000btu radiator? I would think several 8mm or 10mm pipe would be best due larger surface area to tile contact for heat transfer and this would also minimise the height of the tile.

 

[Jamesie]

Ive not touched uf heating, but i have embedded copper pipes in the wall. there is no way i would put the copper submerged without protection, i normally use denso tape, obviously that will absorb heat. maybe the pro's can shed more light on it for you.
and with regard to just placing it around the edge of the room, is it really going to be effective at heating/

 

[Agile]

Its difficult to calculate that. Also covering with carpet will reduce the heat output by perhaps 50%.

A rule of thumb is that standard UFH has pipes spaced 200mm so 5m length in a square metre which gives out about 100-150w.

Plastic pipe will transfer the same amount of heat but could have a slightly higher differential but that will make no difference.

Its the medium between the pipe and the room which determines the heat loss. That is limited by the allowable floor temperature which is about 30 C maximum!

Copper should not be buried directly in concrete or it will corrode so that's a no-no.

Tony

 

[denso13]

Copper should not be buried directly in concrete or it will corrode

No it won't, unless the sulphur content is high. Normal concrete doesn't corrode copper..

 

[Agile]

So if it does not corrode why do you have to use Denso on your gas pipes then?

 

[denso13]

Not sure, perhaps a protection against thermal movement because it is a gas pipe, but you would also do this for all pipes, not just gas.

 

[thompo]

Not a plumber but done plenty of research after getting wildly different quotes on what i needed from different suppliers for the same job. 300m-700m of pipe!

Could explain why many people claim it costs a fortune to run and doesnt heat the place. If the system doesnt have the capacity its never going to work.

What i came to use as a rule of thumb for planning my own is below. (Only starting to commission it this week so dont know if its worked yet lol). If anything this is much more conservative (realistic?) than what a lot of the UFH supply websites quote.

Assuming 50deg flow 40deg return (could be 55/45 cant remember off hand), with pipes embedded in a soild screed floor with stone/tile covering (ideal situation in terms of heat transfer) all on top of good insulation (100mm+ of EPS/PU)

100mm spacing = 125w/m² ~ 10m of pipe/m²
150mm spacing = 100w/m² ~ 7.5m of pipe/m²
200mm Spacing = 80w/m² ~ 5m of pipe/m²
300mm Spacing = 60w/m² ~ 3.5m of pipe/m²

Qty of pipe/m can vary a little using different laying patterns

Reduction factors for alternative floor coverings
Light weight carpet -20%
Wood, -30%
Heavy carpet -40%

You really need to think about the area you have and what you can fit into it and then determine if the output is enough.

All the above is for 16mm plastic pipe. Id doubt, in practice, if you would notice much if any difference using copper. Especially using a narrow bore pipe due to reduced heat carrying capacity. You really do not want any joints under the floor.

If in doubt get as much pipe in as possible. You can always reduce the flow rate or temperature if its too warm. If its too cold, your beat without increasing temperatures beyond guideline and risk damaging your floor.

Quick calc, 1800w @ 100mm spacing would need an area of 1800/125= 14.4m² ~ approx 144m of pipe.

Running single loops much more than 100-110m of 16mm if a no no due to pressure drop. Using 8mm the pressure drop will be much larger meaning maybe 4 or 5 loops.

 

[Agile]

Not sure, perhaps a protection against thermal movement because it is a gas pipe, but you would also do this for all pipes, not just gas.

Its a Gas Regulations requirement to wrap gas pipes with correct protection to avoid corrosion when embedded in concrete!

I agree copper does not corrode in DRY concrete but it certainly does if these is any dampness at all.

Tony

 

[denso13]

Its a Gas Regulations requirement

Which one?

 

[Boabie]

Ive not touched uf heating, but i have embedded copper pipes in the wall. there is no way i would put the copper submerged without protection, i normally use denso tape, obviously that will absorb heat. maybe the pro's can shed more light on it for you.
and with regard to just placing it around the edge of the room, is it really going to be effective at heating/

My thought is to equate the radiator value required for the room 1800w and place it under a floor tile around the circumference of the room. I would place the pipe(s) on top of insulating material and have a plywood frame either side of the insulation this would finish level with the top of the pipe(s). The tile would then be adhered to the ply and the pipes using Mapei Ultramastic. I realise the heat transfer would be only around the floor edge but if a radiator hung on a wall heats the room I can't see why having pipe work around the room would not be better as it will spreading the heated zone.

 

[Boabie]

Its difficult to calculate that. Also covering with carpet will reduce the heat output by perhaps 50%.

A rule of thumb is that standard UFH has pipes spaced 200mm so 5m length in a square metre which gives out about 100-150w.

Plastic pipe will transfer the same amount of heat but could have a slightly higher differential but that will make no difference.

Its the medium between the pipe and the room which determines the heat loss. That is limited by the allowable floor temperature which is about 30 C maximum!

Copper should not be buried directly in concrete or it will corrode so that's a no-no.

Tony

Thanks for your reply.
Would be porcelain tile on top of pipes not carpet, Pipe would be in contact with tile and embedded in tile adhesive. Will plastic pipe give off same heat as copper? If so why are radiators made from metal?
I have googled the size of radiator required to heat my room 1800 watt I am trying to find the cheapest way of placing that value under floor. I have looked at full underfloor heating and with special insulating boards and pipes its damn expensive. This combined with carpet, furniture etc lessens the effect of heat to the room.

 

[Jamesie]

I understand where your coming from. The radiator you say you need is 1800w, i would try and exceed 1800w to allow for heat absorbtion. if you do go ahead, good luck, and fingers crossed it works.