Underfloor heating, any plumbers?

[yorkie_chris]

We've got a stove which we burn coal and logs (and anything else that's free and flammable). It came with a boiler in the top of it which we intended to integrate into the proper central heating (condensing type combi boiler fed), but that looks like it's going to be a major pain in the rse. So that idea has been put on the back burner for the moment.

So, plan B. A seperate underfloor heating system just for the one room and part of the kitchen just to use the boiler and extract some of the waste heat from the flue gas.

I've got a reasonable grasp of thermodynamics, and have a fair idea of how to do it, but how would you do it?


P.S the stove has been in ages, but we removed the boiler part to avoid it burning through. It is a simple box welded up out of 1/8" plate 13" x 8" x 2" with a pipe spigot at the rear corners and a 1" hole through the middle of it. Can anyone guess at a rough heat output? And general idea of complexity and cost if we were to go with the original idea of fitting this into the main central heating circuit.

Cheers folks

[skeetly]

whats the floor of the kitchen and the room made of?
I'm guessing its a wooden floor as it'd be expensive to dig up a solid floor to put a pipe loop in and you dont like expensive.
You need a pump to drive the water round as you the stove will be higher than the floor.
If its a wooden floor you wont have a solid mass to heat up (and hold the heat) so you wont get much hot air convection from the pipe (which is what radiators do best despite their name). Easiest and cheapest way with a stove is an extra rad somewhere but it would have to be on a seperate 'open' system away from the existing 'closed' pressurised system (unless you want to pay for certificates etc etc)
A boiler will soak up some heat from the stove.
Leave doors open and let heat from stove work its way round house and put thermostatic valves on the existing rads. They will close sooner if the stove helps heat up the rooms.
Its what we do with out log burner.

IF you really are planning on digging up the floor then things are different

[yorkie_chris]

There is easy access underneath the sitting room and part of the kitchen, we were considering putting pipes under the wood in between the joists then putting some of that thin foil backed foam in between the joists, and also sealing up some of the numerous drafts.

[skeetly]

I've mucked about a lot with underfloor heating and it works best when you can dribble heat into something big that will soak it up and release it slowly at not much watts but over a large area. Upshot of this requirement is that its most efficient with a gas boiler (as you can modulate the firey bit easier) that is left on all the time to keep the thermal mass topped up.
Pipes under the floor just radiate the heat. This doesnt work so well as the bloody things are round albeit long
Wooden floors are good insulators so you wll end up with nice warm pockets between your floor joists.
Draughtproofing and insulating the floor alone would probably make a huge difference.
My moneys on kill the draughts, fit thermostatic valves to the rads (if they aren't there already) and let the mighty stove heat the air in the room when you are running it and the valves will close off the rads and the c/h boiler will use less fuel.
I'll bet it will be a more efficient use of your wood/coal/tyres/lost southerners.


edit: I know this works as I have done it in our built in 1801 stone cottage.......

[yorkie_chris]

You make a fine point.

My second idea is a heat exchanger above the stove. As it stands (I think because we have no top plate, as we removed the boiler) the stove is very inefficient. Loads of draught, the stove roars like a jet engine with the draughts open and door closed, but little heat into the room. And will not drop down to a slow "simmer" to stay lit overnight.
I think it's just a poorly sealed stove coupled with a long, well insulated chimney causing this, so what about an air-air heat exchanger above the stove. There's a huge dead space above the stove in the chimney and I could weld something up in 316L stainless to suit and blow the hot air into the room.

[yorkie_chris]

N.B The reason for this sudden move to efficiency, we recently had to actually PAY for coal! And that's not a good state of affairs.

[skeetly]

Bet it would have to be pretty thick not to warp. I can see it glowing now

If the air cant move upwards because of a narrowed flue then its going to move faster; cue jet engine effect x 10.
Your exchanger would need to get rid of heat pretty quick
Normally you would control the burning rate by reducing the avilable air but thats not an option unless you seal the stove.
You could of course control it by adding small amounts of fuel often but thats a pain.

Being as you can do things metally; how about a new baffle plate inside the stove where the boiler used to live and seal the stove properly?
You can control them lovely when they are sealed.

I have a story to tell here. Many years ago i bought a Much Wenlock stove with a back boiler on it. It sat filling the inglenook for years as I could never find the time to connect the bloody thing. When I got round to it I found there was so much work involved sealing the thing, removing the back boiler (was full of dry sand from the previous owner but there were too many tales of exploding boilers). making a back plate to replace the boiler, cutting and fittign a baffle plate etc. that I just went out and bought a brand new 5kw little wenlock stove.

http://www.firesonline.co.uk/acatalo...ve.html#aagalw

The heat is insane from it. At full tilt we have to open every door in the house as its so hot. So I run it at half speed when its cold and it tops up the c/h.
I have killed *all* the draughts and dry lined the external stone walls though; this made a huge difference.

I love stoves

[skeetly]

Originally Posted by yorkie_chris

N.B The reason for this sudden move to efficiency, we recently had to actually PAY for coal! And that's not a good state of affairs.

Considering it sounds like you have a nice flue alreay in there I'd buy a new stove tbh.
Get a good one though.

That page i sent you the link form is run by our local stove emporium and they *really* know their stuff. I doubt they have any rubbish stoves in their inventory.

http://www.homeandheating.co.uk

[DarrenSV650S]

I love the heat you get from real fires. It's awesome

Sorry, nothing helpful here, just wanted to add that

[yorkie_chris]

Yes for temporary fix I have my mate cutting me a decent slab of steel to replace the boiler.

New stove is not an option!