Constructing underfloor heating system from scratch

[vexation]

Planning to heat a new-build 18sq m extension with wet UFH but without resorting to an off-the-shelf kit. I have several reasons for not wanting to buy a kit - I think they're generally over-priced for what they contain (I've seen standard looking £60 CH pumps thrown in with a couple of isolators and a mixer maybe worth £25 sell for over £300). Also I don't want all the kit components (for instance I have my own custom control electronics already integrated with the rest of our CH system that monitors and controls as many zones as I like).

Two questions then arise: can the barrier pipe for the underfloor loop just be regular PEX such as a 100m of 15mm SPEEDFIT PE-X BARRIER PIPE (it's never clear to me if the kits supply something subtly different/special or not) - and where to get an automatic valve that mixes a variable amount of return with feed to reduce the loop temperature from somewhere around 70C from the boiler to 30C or so for the floor. For example, I've already used some £25 automatic mixers for separate hot & cold taps in our bathrooms to prevent scalding (fantastic bits of kit) and I don't really see why such a valve wouldn't work here.

Given that I've priced all this up at around the £250 mark compared with kits in the region of £500 I think it's worth investigating. Please shoot me down if you disagree!

 

[ericmark]

Clearly as a new build it will have all the insulation fitted, however the problem I find with underfloor heating is speed of warm up, look at kickspace heaters first

OK it may not suit, however they are fast warming the room, and because they circulate the air the floor does get warm.

 

[vexation]

Hi ericmark, yes you're absolutely right about the warmup time but this is a fully double glazed room (think big fishtank) with nowhere but in the floor to put heating. The one wall connecting to house is mostly going to go eventually I did look at trench heating but it seems to be a bit unusual (i.e. expensive). Yes the floor has 100mm of celotex and 150mm in the roof. My calcs show around 3kW should do it but 100m UFH can deliver up to 10kW if required. Some nifty control is planned to minimise response time using this overcapacity.

 

[Dan Robinson]

I think they're generally over-priced for what they contain (I've seen standard looking £60 CH pumps thrown in with a couple of isolators and a mixer maybe worth £25 sell for over £300)

Given that I've priced all this up at around the £250 mark compared with kits in the region of £500 I think it's worth investigating

Champagne ideas - beer money - crack on.


Or should that be "the cost of everything and the value of nothing"?

 

[vexation]

Cost of this stuff is all over the place though. It feels like it's still not mainstream even though UFH is getting quite common. The only supplier that I've found with prices that I could go along with are: https://www.wundatrade.co.uk/
Perhaps someone around here has had experience with them to share?

 

[muggles]

Planning to heat a new-build 18sq m extension with wet UFH but without resorting to an off-the-shelf kit. I have several reasons for not wanting to buy a kit - I think they're generally over-priced for what they contain (I've seen standard looking £60 CH pumps thrown in with a couple of isolators and a mixer maybe worth £25 sell for over £300). Also I don't want all the kit components (for instance I have my own custom control electronics already integrated with the rest of our CH system that monitors and controls as many zones as I like).

Two questions then arise: can the barrier pipe for the underfloor loop just be regular PEX such as a 100m of 15mm SPEEDFIT PE-X BARRIER PIPE (it's never clear to me if the kits supply something subtly different/special or not) - and where to get an automatic valve that mixes a variable amount of return with feed to reduce the loop temperature from somewhere around 70C from the boiler to 30C or so for the floor. For example, I've already used some £25 automatic mixers for separate hot & cold taps in our bathrooms to prevent scalding (fantastic bits of kit) and I don't really see why such a valve wouldn't work here.

Given that I've priced all this up at around the £250 mark compared with kits in the region of £500 I think it's worth investigating. Please shoot me down if you disagree!

The difference is to do with warranty and insurance. Yes you can cobble together a kit of parts out of the cheapest bits you can find on the Internet, but then what happens if you get a leak, or a failed mixing valve, or some other issue? Who do you turn to? Can you be confident that the manufacturers of your cobbled-together parts will back you up? Will they cover your consequential loss as well?

 

[Hot&Cold]

Just because anybody can purchase the materials does not mean its installation is diyable but its your property your risk

 

[vexation]

Thanks for showing some concern here. No worry necessary. I've previously fitted a few bathrooms, kitchens and CH rads without any trauma so I guess I'm just seeing a bit of inflated pricing where others don't. Spending more time searching around for small single zone UFH kits it's pretty clear that there are plenty of alternatives to the 'Screwfix' type of retailer and big name builder's merchants and I will probably end up with one of them.

 

[dhutch]

Surely you would buy an underfloor mixing valve separately from the kit. Thus getting the right hardware, outside of a kit, if the kit is priced silly or doesn't do what you want for some reason.

It might that a TMV designed for a wash hand basin will give the same results as a simular looking UFH mixing valve, but a quick search seems to suggest prices are similar anyway so why would you.

Daniel