Fire back for woodburner

[John Carlyle-Clarke]

We had a standard 22" square open fire with a clay fireplace. We've now removed this with precision hammers, and are in the process of getting a woodburner installed.

I want to put something in behind the woodburner, for two reasons: firstly, to tidy up the appearance by hiding the rather unsightly brickwork, and secondly to reflect heat back out.

I was thinking stainless - basically about 2' x 4', with the sides folded round to fit the hole.

I've been quoted 90 quid for heavy gauge mild steel, painted in black stove enamel, and 180 quid for stainless (apparently it will need to be good quality to stand the heat, which makes sense).

I'm happy enough with black painted steel from a cosmetic point of view, but I'm wondering about heat reflection. My memories of physics lessons suggest that if the front is painted but the back is left unpainted, it will tend to absorb heat and re-radiate it back into the room. Is this correct?

[Andy]

Silver will reflect heat, black will absorb and when the fireback has heated up enough, reradiate. The cheapest option IMO is to go for a black painted fireback, with a bit of rockwool behind it. You can make space for an inch or two of rockwool presumably?

Andy.

[Stewart Devereux]

We have had numerous wood burners over the years, some with similar problems to yours. First you must be aware they can generate ALOT of heat, so metal might not be the best idea. I would go along with first reply. 1-2 inches loft insulation pinned to brick, then cut a piece of fireboard to size and cover. Can easily be painted matt black. The burners work best by allowing air to circulate around them-I don't think once you have it up and burning you will be worried about reflecting heat back in !

[John Carlyle-Clarke]

Thanks for the reply, and to Andy too.

This one is a tiddler, and only 4kW. Nonetheless, I agree it should put out a lot of heat.

One installer told me they could not put it in without enlarging the aperture, because all the heat would get absorbed by the brickwork and none would come out into the room.

Another installer (the one I want to use) said that was true, but he proposed to use a 90 degree elbow from the back rather than the top, and put the unit 3/4 way out of the hole, so only 1/4 of it is inside the aperture.

That is really why I was thinking about the reflective qualities of the backing, but I guess with a stove obscuring most of the opening, re-radiated or reflected heat from the backing is not going to make much difference.

[HLAH]

I think you may be missing here one the greatest benefits of woodburners. Whilst the stove is burning the room is heated by radiant energy whilst the mass of the brickwork around the stove warms up and stores the heat. That heat is then released slowly over time even when the stove is out. Of course if the wall behind is an exterior wall then it's going to be a lot less efficient.

Our front room , which besides having a woodburner has an inadequate radiator, is a much nicer place to be for at least a couple of days after having had the woodburner running.

Some woodburners are designed to use the thermal mass of the brickwork around the stove to store energy and increase efficiency. Google for "russian stove" to see examples.

H

[The Natural Philosopher]

cheapest is to render the whole fireplace frankly..I've got a rendered behind the stove back. It works well

Stoves don't put out fierce heat to the fireplace, unlike an open fire. They radiate a far more even heat - the high temps are all inside, as you will discover when firebricks disintegrate and grates buckle and bend. And finally oxidise and fail ;-)

When you operate solid fuel devices, you get to understand how primitive man discovered how to smelt metals..

Also bonfires on clay soil make quite GOOD lumps of brick..

[The Natural Philosopher]

And where does he think the heat will go when the brickwork has absorbed it?

I'd say that was a plus. My massive open fire chimneys and masonry surrounds may take three hours to warm up, but they keep the temperature up all night afterwards..and in summer, down all day too.

The aga flue heats the bedroom upstairs as ell.

Nope. Render it. All you really need is an air gap around it to allow convection off it to come out to the room, A couple of inches is fine.

The actual stove temps are not that great. Couple of hundred C at the most outside. OK too much for wood, and maybe plaster, but fine on masonry and render.

Or as John says, use some fireproof board painted black. Thats quick and simple. and will let less heat into the structure than render. But I think render - with sharp sand and white cement - looks nicer.

4KW is a powerful fire. The UFH in my house is rated at 100w/sq meter. Thats 3KW in a 6x5 sq meter room. I get a rate of rise of about 1 deg C per hour with that..the open fires do about three times that once the brickwork is warm.

I think you are going to love that stove.

>

[The Natural Philosopher]

Mmm. My sister had one of those things installed in a house in Germany. Its basically a stove built into a vast brick and concrete block structure with convection vents and double skins.

It certainly made a great space heater, till they got too old to faff around carting fuel for it. Also a great room COOLER in summer, when unlit.

Agas are the same. A quirky and indifferent cooker, but the best and most efficient space heater I have ever used. The flue is cool to the touch..all the heat goes into the room. FAR better efficiency than any pumped boiler. Even the heat that DOES go up the flue ends up in the room above.

Also useful in summer when unlit to keep daytime temps down.

[John Carlyle-Clarke]

Thanks for all your comments. I thought the same thing about the brickwork, but the HETAS registered installer that I spoke to first was so firm about it being a problem that I assumed he must be right and I must be wrong. It is an internal wall.

Rendering I suppose is a good solution, and cheaper than the £90 for painted steel.

I'm hoping we're going to love the stove too :) This room is also about 6m x 5m.

Here is the little beauty.