Wall insulation behind log stove

Another Dave

unread,

Dec 21, 2010, 3:01:48 PM12/21/10

to

The dining room/parlour of my 1928 house has a log-burning stove set
into the old fireplace. This means there is one leaf of bricks between
me and the outside world. Three questions:

a. Can I put some insulation on the wall? There's a 4" gap behind the
stove but it gets hot - what should I use?

b. Is it worth doing?

c. There's a similar arrangement in the lounge but with a coal-effect
gas stove - I assume the same answers apply?

Another Dave

John Williamson

unread,

Dec 21, 2010, 3:16:50 PM12/21/10

to

For a quick and easy test, try lining the back of the recess with
aluminium foil. If it helps noticeably, then replace the foil with a
sheet of unpainted metal with an air gap behind it. The heat there is
mostly radiation, so the foil/ metal will reflect this back.
--
Tciao for Now!

John.

andrew

unread,

Dec 21, 2010, 5:07:11 PM12/21/10

to

John Williamson wrote:

>> a. Can I put some insulation on the wall? There's a 4" gap behind the
>> stove but it gets hot - what should I use?
>>
>> b. Is it worth doing?
>>
>> c. There's a similar arrangement in the lounge but with a coal-effect
>> gas stove - I assume the same answers apply?
>>
> For a quick and easy test, try lining the back of the recess with
> aluminium foil. If it helps noticeably, then replace the foil with a
> sheet of unpainted metal with an air gap behind it. The heat there is
> mostly radiation, so the foil/ metal will reflect this back.

Yes, I like the idea of a curtain of foil, open top and bottom, to reflect
heat plus allow a convection path, the back wall still needs a non
combustible insulation though and watch the distances comply with part J.

AJH

Tim Watts

unread,

Dec 21, 2010, 6:41:20 PM12/21/10

to

The only things I can thick of that would stand the heat are asbestos,
glass(etc)wool and vermiculite.

Ignoring the first one, one option might be to make up a false back out
of shiny metal (eg stainless sheet) then, leaving as much of a gap as
possible between that and the bricks, fill the gap with glass wool or
vermiculite.

Watch that you leave the required space between the back of the stove
and the new wall surface (my stove wants >=2")

So you might manage 2" insulation if your stove is happy - roughly
equivalent to a cavity wall.

Obviously use nothing remotely combustible back there - no wood battens
- all mountings done in metal etc etc. Rawlbolts could be a decent
method and mount the sheet on studs with nuts both sides to achieve the
required standoff.

It might be worth doing as that section of the wall could run really
really hot during use so the power loss will be significant. Does that
part of the wall outside get hot to the touch?

--
Tim Watts

cynic

unread,

Dec 22, 2010, 5:42:58 AM12/22/10

to

Fibrefrax sheet with a metal panel in front of it

harry

unread,

Dec 22, 2010, 5:52:26 AM12/22/10

to

On Dec 21, 8:01 pm, Another Dave <dmars...@nospam.com> wrote:

Definitely worth doing. It will all have to be fire proof of course.
You can use mineral wool finished with fibre cement board, spaced away
from the wall with the metal studding intended for partition walls.
A shiny finish (cooking foil?) would be good.

The Natural Philosopher

unread,

Dec 22, 2010, 8:55:47 AM12/22/10

to

Tim Watts wrote:
> On 21/12/10 20:01, Another Dave wrote:
>> The dining room/parlour of my 1928 house has a log-burning stove set
>> into the old fireplace. This means there is one leaf of bricks between
>> me and the outside world. Three questions:
>>
>> a. Can I put some insulation on the wall? There's a 4" gap behind the
>> stove but it gets hot - what should I use?
>>
>> b. Is it worth doing?
>>
>> c. There's a similar arrangement in the lounge but with a coal-effect
>> gas stove - I assume the same answers apply?
>>
>> Another Dave
>
> The only things I can thick of that would stand the heat are asbestos,
> glass(etc)wool and vermiculite.
>

Masterboard will take heat up to dull red. Its a glass/cement board I think.

I used it when soldering plumbing, and to make up stove surrounds

Expesnive, but works.

Insulating properties similar to plsterboard.

Foil covering is possible, but not that much use id say.

Andy Dingley

unread,

Dec 22, 2010, 11:07:40 AM12/22/10

to

On Dec 21, 8:01 pm, Another Dave <dmars...@nospam.com> wrote:

> The dining room/parlour of my 1928 house has a log-burning stove set
> into the old fireplace. This means there is one leaf of bricks between
> me and the outside world. Three questions:
>
> a. Can I put some insulation on the wall? There's a 4" gap behind the
> stove but it gets hot - what should I use?

It's hard to do this in such a small gap. There are also regulatory
limits on how close you can get.

One of the best ways (and cheap) is just a sheet of steel, with a
large air gap on its cold side and enough gap above and below to allow
air circulation. This acts as a radiation barrier between stove and
wall, and becomes a convection heater in its own right. Most modern
box stoves are double-walled for just this reason. You can also mount
this on the rear of your stove (useful for regulatory gap
measurements), although it's useful if it's also shielding the flue
outlet (using two plates can be useful, one notched to clear the flue,
the other covering this gap from the back). The reason it works is
because of the Stefan-Boltzman law - radiation is proportional to the
fourth power of the absolute temperature. So a hot stove radiates a
lot of power (into the cold wall), but this cooler plate will radiate
far less of it into that wall. Your lossy wall now has less valuable
energy hitting it for it to lose - this reduces the waste at source,
also reduces the wall temperature and thus the difficulty of
insulating it.

I have a similar problem in the near future, and I'm planning on
adding insulation to that wall over a fireplace-sized patch, but doing
it on the outside rather than the inside.

Dave Starling

unread,

Dec 22, 2010, 11:34:45 AM12/22/10

to

On Dec 22, 4:07 pm, Andy Dingley <ding...@codesmiths.com> wrote:

> One of the best ways (and cheap) is just a sheet of steel, with a
> large air gap on its cold side and enough gap above and below to allow
> air circulation.

Taking this one step further, why not fit a single rad with fins on
the wall. Does the same job as a plain sheet of metal, plus the fins
will give you much better heat transfer and you have the stand off
from the wall.

Whether you plumb it into anything or leave it open ended is a good
experiment.

Dave.

Another Dave

unread,

Dec 23, 2010, 11:05:00 AM12/23/10

to

I'm the OP.

I didn't make myself clear, sorry. I'm not interested in retaining the
heat of the log stove - the room gets so hot when it's running we have
to open the door to let the heat circulate through the rest of the house
;-) I only run the stove when the temperature gets below 5C i.e. every
day for the last month.

However, the single leaf of bricks (1.5 M square) must lose a lot of
heat at other times when I rely on the central heating. Thanks for all
the suggestions - I'll report back when I've done something about it.

Another Dave

george [dicegeorge]

unread,

Dec 23, 2010, 7:15:05 PM12/23/10

to

On 21/12/10 20:01, Another Dave wrote:

cant you put insulation on the outside of the wall?
[g]