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Author Topic: Is it reasonable to use a wood stove to run underfloor heating?  (Read 6834 times)
Bobby
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« on: April 25, 2007, 09:33:55 PM »

Hello,
This is probably a bit of a naive question but I'm interested in the simplicity of running water based underfloor heating via a solid fuel stove as an installation in a new house. However I'm meeting with a lot of resistance from plumbers and heating engineers. Is the logic fundamentally flawed about doing this? My hope would be to use  the stove to heat a vented tank and then the UFH would take a feed from that tank via its own manifold pump. I'd have thought that by positioning the inlet to the UHF manifold at a suitable place in the tank it would ensure that the water going into the floor was not too hot.

Am I missing something here, is it something other folk have tried? I've seen UFH hooked up to a solid fuel rayburn in another new house build but I'm not sure how well it would work with a standard stove or what size of stove you'd need.

Thank in advance, top forum by the way, its great for getting credible unbias advice.

cheers
Bob
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Ivan
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« Reply #1 on: April 26, 2007, 01:24:24 AM »

No reason why you cannot do this, as far as I can see....
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stephen
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« Reply #2 on: April 26, 2007, 09:26:32 AM »

Bobby,
I have worked closely with Uponor on several prototype buildings using under floor heating in various applications. Uponor produce the underfloor heating and are possibly the biggest in the country.
Try giving Tony Byford a call at Uponor 07710 276841. He should be able to put you in touch with one of their technical guys.
I see no reason either why this cannot work. I also intend doing this with a biomass boiler in the near future when I need to replace my room floor (which won’t be long).
You may need a heat leak rad / heat dump though as the underfloor heating will not get rid of heat fast.

I don’t think you will be disappointed with the under floor heating when its in.
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ecogeorge
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« Reply #3 on: April 27, 2007, 12:05:21 AM »

YES!! DO IT.
Thats my system, woodburner coupled  directly to vented cylinder. Take hot feed to floor manifolds from top of cylinder but run manifold via thermostatic valve using floor return as cold supply. Vavle will only let hot in if valve is returning cold to (btm) of tank. If you have an indirect tank that leaves a coil unused which I intend to use as solar input.
I put a pipe thermostat set at 35c on the top of the tank so the underfloor heating pump will only run if hot water is available to satisfy the demand. Have promised many people a schematic and will try to create one but it's not rocket science.
Plan to add  heat pump input as well asap -time!!!
rgds George.
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Bobby
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« Reply #4 on: May 04, 2007, 09:09:17 AM »

Thank for the responses. I'll get in touch with upanor and look forward to seeing ecogeorge's schematic.
cheers
Bobby
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wookey
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« Reply #5 on: May 25, 2007, 01:49:15 AM »

Yeah, me too. I have found this thread fascinating as is covers many of the issues I am trying to work my way through now. I want to combine solar and wood-burning stove in most efficient fashion, with gas/electric/heat pump top-up. Ideally I would generate the enthusiasm necessary to make a hell of a mess and  change to UFH too.

I have not yet fully understood the tradeoffs of coils vs direct heating, big store vs small hot water tank, thermal stores with tappings at different heights, requirements for heat dumping from wood-burner and panels in summer, separating/joining DHW and CH systems etc. None of it is very difficult in principle but the interactions and mulitude of use scenarios makes it surprisingly complicated. And hot water tanks have got so much more complicated since last time I looked!

One thing no-one seems to mention is power consumption of pumps. I've seen 100W mentioned, and some of these setups have several pumps. If they are running for a lot of the time that could be a non-trivial electricity use.

Once I have done some sums and bit more thinking I'll be able to ask some more intelligent questions.
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Wookey
Ted
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« Reply #6 on: May 25, 2007, 08:39:23 AM »

The Grundfos circulation pumps I use have got 3 selectable throughput settings. These consume 130W, 175W and 190W respectively. They don't run 24/7 of course but, even so, the power consumption is significant enough that it needs to be taken into account.

[edit]
Having said that I thought I'd better actually measure one. Turns out to be 130W, 149W and 172W so not quite so bad.
« Last Edit: May 25, 2007, 08:48:02 AM by Ted » Logged

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lightfoot
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« Reply #7 on: May 30, 2007, 09:58:21 PM »

This is all very simple, maybe consider a thermal store instead of a standard hot water cylinder, as for controls please see the following link to save me alot of typing.

http://www.termoventiler.se/default.asp?webb_ID=110&webbsida_ID=56

A thermal store is used to store energy in the form of hotwater (80 deg C), this hotwater is then be used to to provide space heating and hot water on demand.

The DHW (hot taps) is supplied by passing cold water direct from the mains through a coil in the top of the thermal store, this heats the water instantly by conduction.  For saftey the tempreture of this water is then normally regulated by a thermostatic blending valve before it arrives at the taps.

The hotwater in the thermal store can be pumped directly around the underfloor heating circuit or via a coil in the store like the hotwater, either way you should have thermostatic blending valve between the store and floor to prevent damage caused by high temps.

A thermal store should be sized with both the demand and the recharge interval in mind, the bigger the store the more energy it can hold between boiler firings.  For example if configured correctly a 500 litre store heated to 80 deg C could hold around 23 kW of usable energy.

all the best

Lightfoot.
« Last Edit: June 02, 2007, 02:42:35 PM by lightfoot » Logged

Mother Nature is a wonderful housekeeper - but eat her out of house and home and you may just get your marching orders.
Phil
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« Reply #8 on: May 30, 2007, 10:25:41 PM »

Hello,
  I use a Wood fired Rayburn with high output boiler and 30 Tubes to heat a thermal Store which inturn via a coil feeds a wet two zone underfloor heating system.  in a small stone cottage.

It works but you need a good head of steam to warm the floor.   We have a 3-5 inch thick slate floor which takes a good 5/6 hours to warm up but this will easily use all the heat in the store this is with the Rayburn running flat out.  and then its bath time oops  Shocked   
My advice is yes it works but get the biggest thermal store possible and have the smallest distance possible from your underfloor heating pipes to the floor surface you want to heat up.
oh yes and be prepared to go without a bath for warm feet.
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