Insulating / sealing around fire box

[dmck1122]

I have spent the morning looking at / pulling apart our fire - it's a Masport (Australian brand) inserted into an old chimney and I've always knew there was cool air being drawn from the chimney cavity into the room - mainly when the fire fan is running.

Once the fire sides / surround were off it's clear that whoever installed it didn't worry about sealing it all up: there is 150mm space on either side of the fire box and a 100mm gap at the top to the lintel, and then empty space above the fire and flue. The chimney cavity is pretty big so there's a lot of room up above the fire box.

The fire itself seems to be working as it should - the sides are a little hot and top of the box not at all. So any heat generated seems to be heating the baffle plate and the (noisy!) fan pushes air from the front bottom inlet around the fire box and out the top vents.

The flue temp near the fire box is around 100-120 degrees C - is this normal?

I spoke to a fire retailer and they recommended using Hebel blocks to pack around the fire box and then use a sealer between the fire place and the surround plates. I guess the Hebel will insulate a bit?

So I'm wondering if following the Hebel block advice is good to stop the draft? Should I also look to insulate around the flue as well? Or above the firebox?

 

[Grisu]

Welcome to the forum!

Does the chimney have a(n) (insulated) stainless steel liner all the way to the top? Here is a pic: (broken link removed to http://www.woodlanddirect.com/core/media/media.nl?id=120894&c=483668&h=e91c29bb40e5daffa7ec)
If not, you definitively need to have one installed to improve the performance of the insert and for safety reasons. It will also be much easier to clean in the future. Make sure to have the chimney cleaned professionally before the install.

To keep the heat in your home you should then get a block-off plate with some mineral wool (e. g. Roxul insulation in the US) on top. Here are some instructions how to make one: https://www.hearth.com/talk/wiki/make-a-damper-sealing-block-off-plate/ It is usually not that difficult but you will probably need to pull the insert out.

First, is your fireplace at an interior or exterior wall? At an interior wall you only need to insulate the flue but not the walls as those will radiate the heat back into the room. At an exterior wall insulating around the insert can help provided you have enough space. I looked up those Hebel blocks and found a r-value of 9 to 11 for an 8 inch (20 cm) block. That is not that great although better than nothing. Some members here used Roxul batts to insulate around their inserts, here is a thread about it: https://www.hearth.com/talk/threads/finally-got-around-to-insulating-my-fireplace.75755/ Maybe you can find a similar product in your place?

The flue temp near the fire box is around 100-120 degrees C - is this normal?

That sounds low but since I am not familiar with your insert I am not sure what you should be seeing. After looking at the manual it looks like is a secondary burn insert similar to the models sold here in the US. How dry is the wood you are burning? How much can you close the air control without smoldering the fire? When you don't have a liner I would not be surprised that the insert is not putting out that much heat.

 

[begreen]

Pictures of the existing setup and concerns would help a lot here. Is there a full liner on the stove?

 

[dmck1122]

Welcome to the forum!

Does the chimney have a(n) (insulated) stainless steel liner all the way to the top?

Not that I can see - nor does it have a block off plate - thanks for the link. I suspect its literally being put into the old open fire chimney with only the flue.

First, is your fireplace at an interior or exterior wall?

Interior....but it's a double chimney with the other side / back in a bedroom and this is unused....and not sealed either!

That sounds low but since I am not familiar with your insert I am not sure what you should be seeing. After looking at the manual it looks like is a secondary burn insert similar to the models sold here in the US. How dry is the wood you are burning? How much can you close the air control without smoldering the fire? When you don't have a liner I would not be surprised that the insert is not putting out that much heat.

I'm sure it's a similar model - they're quite widely sold here. Nothing fancy about them but work well enough.

The wood is dry and seasoned - I don't think fuel is an issue.

I can close down the vent to the minimum and it still burns ok - will slowly die out in a couple of hours of you close it down and leave just 1-2 medium logs on there.

 

[dmck1122]

Pictures of the existing setup and concerns would help a lot here. Is there a full liner on the stove?

No liner as far as I can tell - the view is limited to me sticking my phone camera into the cavity and shining a torch.

I'll upload some photos.

 

[dmck1122]

Front of fire with surround sides removed. Gap either side is 150mm

 

[dmck1122]

View up the chimney - there is a bend before it exits.

 

[dmck1122]

Top of fire box / flue

 

[dmck1122]

Closer view of the side gap

 

[Grisu]

Have you checked your manual whether the clearance to the wood trim is ok? I don't know of any unit here that could be installed that way. My surround often gets hot enough that it would scorch any wood trim that would be as close as in your picture. Please do that first before even lighting another fire in the insert.

You don't have a liner but stovepipe in your chimney. Pipe sold in the US would not be approved for that kind of application; not sure about down under. I would ask a certified chimney sweep if that is permissible. Once you have figured that out you can think about a block-off plate. How tall is the chimney from the top of the insert? What angle does the bend have?

Do you want to heat the bedroom on the other side or not? If yes, the only thing to do would be to close the damper of the unused chimney/fireplace there. I would not worry about the gap on the sides; that heat will end up in your home eventually.

Your dirty glass suggests that either your fuel is not as dry as you think or you turn down the air too much/too early. How long has the wood been sitting split and stacked out in the open with lots of sun and wind? When in the burn do you reduce the air and how much do you close it?

 

[begreen]

I could be mistaken, but besides the wrong pipe in the chimney (not stainless?) it looks like the chimney was not cleaned first. This could be quite a dangerous combo, especially with an uninsulated liner. Looks like this needs to be re-done after a proper and thorough chimney cleaning first.

 

[dmck1122]

The glass I clean each day but it does get a little sooty - mainly if wood is near the door or when left to slow burn at night when we go to bed. I don't think I cleaned the morning I took those pics

I don't have the manual so will try and find one on the net. The fire was already installed when we moved in 3 years ago. We have found the house has quite a few diy jobs that don't meet good standards!

The sides and top of the insert don't get hot - they're quite separate from the main fire box and even when burning full on you can easily touch them. That said I agree it needs checking.....so looks like I need it all pulled out and redone + some proper sealing etc