Underfloor Heating; How to??

[Shox Dr]

I'm on with a workshop extension. Heating wise I'm going to fit a Woodburning stove. Thinking about it, I could fit a back boiler to the stove for underfloor heating, spreading the heat around the place better and also keep some latent heat in the place for the next day, as the concrete floor would store the heat.

It goes without saying it needs to be cheap cheap cheap

Has anyone suggestions, comments etc

 

[superls]

in theory its possible, how cheap depends how you do it, i had a similar thought but not underfloor heating, i was going to use some radiators, mainly as ive already built the place and laid the floor etc.

what i was/am going to do was/is fabricate a sort of heat exchanger that fitted to a wood burner and a cheap central heating pump to circulate the hot water.

for underfloor i look to see what is available, or lay some pipes under the floor, plastic/ptfe tube would be better as copper would crack if the floor moved.

 

[piman]

Hello Shox Doctor,

I think it will not be very effective unless you first put a layer of insulation down then a floor screed. Quite a bit of work?

Alec

 

[Shox Dr]

Totally New floor, so will be insulated

 

[piman]

Hello Shox Dr.,

OK, that's fine. You just need the right pipe work, lay it out and fit a pump and thermostat (I'm assuming just one room?). I'm sure that the web will provide details of length of pipe required etc?

Alec

 

[mike os]

unfortunately plastic pipe is not suitable for connection to unregulated heat sources like back burners... & thats what we usually use for UFH

if it gets too hot is will fail, guide temp is usually 80-90c & max safe operating 110c (for the pipe not heating) back boilers can and do boil & then you have leaks & no heating.

 

[MrFluffy]

Thats why you fit a thermostatic blending valve on the actual manifold itself, he says posting all nice and warm from a house with underfloor heating, heated from a wood/oil furnace currently running on wood alone with 90 odd degrees in the main water loop blended down to 40 for the ufh system.

Wood burner -> blending valve, manifolds, circulation pump, return to wood burner.
The moneys in the work and the fancy controls, coils of proper oxygen barrier pex pipe are buttons compared to them. Or, you could just rely on the temperature you set on the mixing valve and maybe some of those little plastic screw temperature adjustment caps...

 

[MrFluffy]

to fill in the gaps, the blender blends the incoming hot with colder water that is returning from the floor slab having emitted its heat.
Your controls pack should turn off the circulator when the floor isnt removing any heat or the blender wont be able to downmix by dint of having too hot water on its cold side.
But thats where if you dont have a fancy control pack, you have a thermostatic valve instead that only flows water into the actual circuit when the return temperature is below a certain value...

Ours turns off the circulator for just the ufh. THe radiators to be upstairs will continue to be in the loop to offer a overheat dumping zone for the boiler itself to dump its excess heat out...

If you dont have hot water in there, you can fit a dual core tank, circulate the boiler pipework through it, and have hte second coil for potable water. Then the tank acts as a big heat sink/storage tank for energy too, plus you get hot potable tap water on demand to boot ;D

 

[Sam]

You will have to run the pipes at 200mm ctrs and attach to a manifold like the pic shown.
There is a high density insulating board which is suitable for under concret I installed this under the concrete in my workshop but cant see any benefit to be honest the only other thing I can see about running the heating from a wood burner I take it you are talking about a bottle with a piggyback boiler attached is when you lose the heat from a concrete slab it can take a while to get the slab back up to temp. p.s. beware when you fix anything to the floor.

 

[mike os]

I thought the proviso was cheap cheap cheap..... blending valves, manifolds & UFH pump is over half the material cost for UFH

 

[the snooper]

I thought the proviso was cheap cheap cheap..... blending valves, manifolds & UFH pump is over half the material cost for UFH

radiator sound better for a workshop especially if there is a chance of dropping something very heavey that will damage the pipes

 

[Smashy]

What about thick socks and a fleece jacket?

I will grab my coat (fleece) on the way out and make sure I shut the door behind me.

 

[Sam]

radiator sound better for a workshop especially if there is a chance of dropping something very heavey that will damage the pipes

Would have to be freekin heavy to go through 4" concrete minimum if in a workshop enviroment. As the saying goes "you canny get a silk purse oot o a sows lug!!!"

 

[MrFluffy]

I thought the proviso was cheap cheap cheap..... blending valves, manifolds & UFH pump is over half the material cost for UFH

Yep. 45 quid for a reliance blending valve, about the same for a circulator and they sell manifolds in the local diy merchants for about 15e apiece here, although if you want thermostatic controls on individual zones you have to buy the manifolds from the same manufacturer as the controls. My manifolds came from the manufacturers of my controls and I added the circulator and thermo controls myself as they say its not part of their bit of the heating solution. Ive done a 120m2 per floor house for under £1000 including postage for some parts from the uk and some sourced locally + the price of concrete of course.

Or, buy the manifold, circulator, manifolds and thermostatic controls as a kit. Found one on ebay uk for 200 quid for five zones. Overkill, maybe theyll do a 2 zone kit or something at cheaper if you contact them...
http://cgi.ebay.co.uk/Underfloor-Heating-Manifold-5-Zone-Pump-Thermostat_W0QQitemZ160376757175QQcmdZViewItemQQptZUK_Home_Garden_Hearing_Cooling_Air?hash=item2557331bb7

Then a roll of pex pipe,
http://cgi.ebay.co.uk/UNDERFLOOR-HEATING-PIPE-16-x-2mm-PEX-AL-PE-100m_W0QQitemZ150359167793QQcmdZViewItemQQptZUK_DIY_Materials_Plumbing_MJ?hash=item23021ad331

Some insulation, the kingspan Sam has above is about the best you can get and quite well priced. I rang up sheffield insulation and buy it in bulk and were impressed with how cheap they were.

Is that cheap? the concrete will cost more than the price of the components. And price up a radiator system, when you get into buying trv's for the radiators, the rads themselves and all the fittings etc that will be needed, it will cost more than the underfloor...

Mr shox, If you heat it later on, itll still be warm in the morning, especially if you have the extra heat storage tanks. We damp down our furnace with the flaps at night, fill it with logs in the burn chamber and 8 hrs later its still burning through the logs so doesn't need re-lighting in the morning. Sam's spot on about the time taken to get the slab up to temperature initially, 10-12hours of feeding logs in with it running at full chat is what it takes here...
As a heat on demand thing for a building largely or partially unoccupied, theyre not good. If your going to be needing it to be warm all the week theyre great.
Also your machines will love it, slow steady background heat = no condensation, stable temperatures for metrology etc...

Im putting ufh into my workshops that Im doing when we finish upstairs. For certain... My last workshop I just ran a wood burning stove in the corner and the radiated heat was fine, if you really want cheap cheap