underfloor heating

[willie68]

I'm doing a loft conversion, it'll be more of a walk in cupboard than a bedroom. I don't need to heat it so much as keep the damp out and rather than put in a proper underfloor heating kit I thought I'd just run pipe from the central heating pump under the loft flooring and back to the first radiator, possibly with tees and valves to bypass the loft if necessary.
We only have six radiators in the house and the pump will be moved into the loft as well so I don't think there'll be any circulation problems.
Any thoughts or ideas on this masterplan.

 

[Richardthe3rd]

You could use a control like this mate. More information on the Danfoss web site.
http://www.heatingcontrolsonline.co.uk/danfoss-randall-fhvr-p-246.html

HTH

 

[willie68]

Thanks for the advice. I might fit the pipes and get it up and running to see how hot it gets. I'll put a tee in somewhere so I can retro-fit a controller if I need one.

 

[Stephen7]

You cant fit a controller with this Danfoss valve unless you zone it complete independently with a zone valve.
Just connecting to the existing rad heating without overheat protection could result in failure of the pipe.
The Danfoss FHV-R has a built in temperature limiter so should do the job for you depending on the area - typically this should be a maximum of 10m2

 

[willie68]

Fair enough. If I need a valve to stop the pipes from overheating then what protects the rest of the pipes in my CH system?
As far as the loft goes, would a radiator valve (TRV?) do the job?

 

[Stephen7]

The rest of your pipes in you CH system are likely to be copper so no overheat protection is required other than the limit the boiler is set to provide. Typically you circulate through a rad system in the region of 60 deg C which is why a rad system is usually rather hot!
The Danfoss FHV-R includes a temperature sensor / control - make sure you get the valve with this control so the UFH is protected.
The sensor is an additional option to the standard valve which is why I mention it.

 

[willie68]

Thanks again for the advice. I'm planning on using copper pipe under the floorboards rather than the pex or pert types which is why I'm questioning the use of a control valve.
Do you think this will work? In the bedrooms you can feel the warmth of the CH pipes coming up through the floor, enough to make the carpet warm underfoot which is all I really need in the loft.

 

[Stephen7]

There is no reason you cant do this - just don't put too much pipe in the floor running form the rad system or you risk damaging the floor as the temperature could be quite high.
If you are just trying to keep the area 'aired' you should be ok.

 

[willie68]

I think I'll put in a radiator valve just in case it gets too warm. I'm using the 200 year old floorboards that were originally in the bedrooms so I think they've seen enough to withstand the heat. I was thinking of using 10mm copper pipe so I can bend it round and not need any 90's. I'm not sure if pipe that small will radiate enough heat, what do yo think.

 

[Stephen7]

You should be ok with this arrangement - just make sure the circulating pump has enough head to circulate through the pipework, a long length of 10mm can have quite a lot of resistance. Also remember that the start of the pipework will be warmer than the finish so, depending on the length of pipe you use, it may be an idea to put more than one circuit in otherwise you risk hot spots & cold spots so to speak!
Personally I would be using UFH plastic pipe - Polypipe is 15mm OD.
You also need to insulate beneath the pipe otherwise your heat will migrate downwards.

 

[willie68]

Where can I get UFH pipe from? I've seen it as part of a kit but not on it's own. I guess if it's specifically for UFH then it radiates the heat as well as copper pipe and 15mm would definitely be easier on the pump than 10mm. The loft is well insulated and I'm going to cut some notches in the top of the joists and run the pipe on top of the insulation right underneath the floorboards.

 

[Stephen7]

Any merchant is likely to stock Polyplumb - make sure it is the UFH pipe though as they also sell ordinary plumbing pipe. B&Q also sell it.
Most UFH pipe (including that which I sell) is 16mm OD which means that the 15mm fittings will not go on.
Don't be tempted to use a push fit system use compression fittings with pipe inserts.

 

[willie68]

It makes sense to use something that's designed for the job. Next chance I get I'll have a measure up and see how much I need but I guess I'll have to get a proper valve if I use the polypipe.

 

[Stephen7]

Let me know your measurements & I will let you know what you need.
The area you intend to heat may dictate the right kit for you to use.

 

[willie68]

Morning Stephen, floor area is 2m x 3.5m but the space is quite small, 2m at the apex sloping down about 45 degrees so it's not a big volume to keep warm providing I do a good job with the insulation.