Blocking off/insulating masonry chimney

[ColdInOz]

Gday all,

Looking for some advice about how best to solve an issue I’m having.

Recently had a pacific energy true north TN20 Installed in an existing fireplace.

There is a 150mm (6in) stainless steel flue that goes up the existing internal masonry chimney and outside (last 1m/3ft of the flue is also insulated).

However the installers didn’t install what I now know to be a closure or register plate above the stove.

End result is the stove just about heats a pretty small room with all the doors closed but not much else!

Reading on here and some common sense tells me I need to occlude the existing chimney to stop all that warm air from flowing upwards into the chimney breast.

So wanted to run my plans past the hearth.com elders and see if they sound like a good idea:

Going to use a galvanised metal sheet - rectangular placed just above the stove top with a cut out for the stove pipe.

Questions- what’s the recommended thickness for the sheet? What are the best materials use to anchor it in? Also - should I insulate above the metal plate as this will obviously itself get hot and I want to try and capture as much heat as possible - have seen people use things like rock wool for this - can this go right around the stove pipe itself?

I will be able to screw it into the metal lintel at the front but will have to use some sort of mortar around the back and sides.

Last question is a fan - currently the unit doesn’t have one as installer said there wasn’t enough depth in the fireplace to fit one (however can easily solve this by removing some of the masonry at the back - don’t imagine it would need to be that much as the fan only protrudes 90mm from the back and the unit currently isn’t flush with the back) - in people’s experience does this make a big difference?

Wood I’m using is Ironbark (an Australian hardwood- room temp split shows a moisture content of 18%). Think I’ve got the hand of getting the fire going alright and don’t think wood is the issue but definitely admit to being a novice and so welcome any tips on burning technique too.

 

[TomMcDonald]

My advice would be to move that sucker into the room and close the chimney for good.
Even with a block off plate you'll be wasting precious kW heating the bricks.

Your iron bark, if actually seasoned and burning well is not the issue. However, make sure you're taking advantage of the secondary burn system and turn down the primary air appropriately. leaving the air open will just be sending more precious kW up the pipe.

The fan is likely to help but again I'd advise you not to waste your time trying to make do with a suboptimal situation.

Or did you buy the insert version? If so, yes insulated block off plate and yes definitely a fan.

Cheers.

 

[Ashful]

My advice would be to move that sucker into the room and close the chimney for good.
Even with a block off plate you'll be wasting precious kW heating the bricks.

I'd agree with you, if the OP had said it's on an exterior wall. But he seemed to indicate this was an interior fireplace/chimney, which has me thinking it's more centrally-located, and thus any heat going into that masonry is radiating back out into the house. Many people use this to their advantage, as it can level off the high/low swings inherent to heating with a wood stove, creating a bit of a poor-man's masonry heater.

As to the block off plate, it's more a reflector than an insulator, although any fire proof insulation (eg. rock wool or chimney liner blanket) laid above the block-off can only help. The liner should have been wrapped in a blanket prior to install, for best efficiency and safety, although many run without. Depending on several factors (chimney height, how much stack is exposed above roof line, efficiency and burn rates of your stove), this may or may not be an issue.

My chimney installer used only plain steel, not galvanized, for my block-off plates. He used galvanized perf angle steel TapCon'd into the masonry to create a shelf that holds this plain steel sheet and blanket, since that angle is not close to the liner and will never get hot. But I think you want any metal touching a hot liner, collar, or stove pipe to be non-galvanized, as the galvanization gives off dangerous fumes if heated above a certain temperature.

The gauge of steel isn't critical, just whatever doesn't sag, given the span/size of your plate. Mine is heavy sheetmetal, probably close to .063", and two squares with half-moon cutoffs that drop in around the liner on one stove. On the other stove, the chimney opening was so large he used three plates to cover the opening, with a hole cut into the center plate that had to be installed before liner was connected to stove plate. On that one, the plates on either side easily lift out to service the connection.

 

[begreen]

Here are some tips and links for installing a block-off plate.

Why damper seal is needed, block off plate install

Should fireplace inserts and hearth stoves have a metal sealing plate installed at the damper area? Here is the simple answer. It is almost impossible to correctly seal most insert panels to the fireplace front. A lot of air can get through them - this works both ways.....hurts the draft when...

www.hearth.com

A blower on the stove or a fan set so that it blows air behind and around the stove will also help convect heat out into the room.

 

[Solarguy3500]

You are on the right track in thinking about a block off plate to keep the heat from going up the chimney. Others have already provided some helpful advice and links.

I am in the process of installing my insert and I took the block off plate/heat shield idea a step further. In fact, you could very aptly call it overkill or at least overthinking, but I have metal working skills from a previous job as a metal roofer so, what the heck? Why not use them?

I used 22 gauge steel (not galvanized) and made cardboard templates of the back and sides of the fireplace as well as a template for the block off plate that will go above the stove. I then transferred the cardboard templates to the 4'X10' sheet of steel I bought locally and cut out the heat shields and block off plate. On each piece, along the sides that I will need tabs to screw them into the brick, I made another cut line 2" out from my marks from my templates, and bent those tabs in the appropriate directions after cutting the pieces out. It helps to have a really good set of right and left cutting snips, and a good set of metal bending pliers. I originally planned to make the block off plate one piece, but at the last minute decide to do it in two pieces and just left 2" of overlap on each piece to make it easier to insulate above it and install it with the liner in place.
Back heat shields:

Sides:


You can see one half of the two piece block off plate in the background there before I bent the tabs on it.

I have 2" thick Roxul foil faced rigid insulation that I will be installing between the firebrick and metal heat shields to further prevent heat loss through the brick chimney. I also have rock wool batt insulation that I will use above the block off plate. Next winter will be the first test with it installed, so I'll report back here or in my old stove install thread on how it works.

 

[KDubU]

You are on the right track in thinking about a block off plate to keep the heat from going up the chimney. Others have already provided some helpful advice and links.

I am in the process of installing my insert and I took the block off plate/heat shield idea a step further. In fact, you could very aptly call it overkill or at least overthinking, but I have metal working skills from a previous job as a metal roofer so, what the heck? Why not use them?

I used 22 gauge steel (not galvanized) and made cardboard templates of the back and sides of the fireplace as well as a template for the block off plate that will go above the stove. I then transferred the cardboard templates to the 4'X10' sheet of steel I bought locally and cut out the heat shields and block off plate. On each piece, along the sides that I will need tabs to screw them into the brick, I made another cut line 2" out from my marks from my templates, and bent those tabs in the appropriate directions after cutting the pieces out. It helps to have a really good set of right and left cutting snips, and a good set of metal bending pliers. I originally planned to make the block off plate one piece, but at the last minute decide to do it in two pieces and just left 2" of overlap on each piece to make it easier to insulate above it and install it with the liner in place.
Back heat shields:
View attachment 312995
Sides:
View attachment 312996

You can see one half of the two piece block off plate in the background there before I bent the tabs on it.

I have 2" thick Roxul foil faced rigid insulation that I will be installing between the firebrick and metal heat shields to further prevent heat loss through the brick chimney. I also have rock wool batt insulation that I will use above the block off plate. Next winter will be the first test with it installed, so I'll report back here or in my old stove install thread on how it works.

I like this idea!

 

[vbu]

You are on the right track in thinking about a block off plate to keep the heat from going up the chimney. Others have already provided some helpful advice and links.

I am in the process of installing my insert and I took the block off plate/heat shield idea a step further. In fact, you could very aptly call it overkill or at least overthinking, but I have metal working skills from a previous job as a metal roofer so, what the heck? Why not use them?

I used 22 gauge steel (not galvanized) and made cardboard templates of the back and sides of the fireplace as well as a template for the block off plate that will go above the stove. I then transferred the cardboard templates to the 4'X10' sheet of steel I bought locally and cut out the heat shields and block off plate. On each piece, along the sides that I will need tabs to screw them into the brick, I made another cut line 2" out from my marks from my templates, and bent those tabs in the appropriate directions after cutting the pieces out. It helps to have a really good set of right and left cutting snips, and a good set of metal bending pliers. I originally planned to make the block off plate one piece, but at the last minute decide to do it in two pieces and just left 2" of overlap on each piece to make it easier to insulate above it and install it with the liner in place.
Back heat shields:
View attachment 312995
Sides:
View attachment 312996

You can see one half of the two piece block off plate in the background there before I bent the tabs on it.

I have 2" thick Roxul foil faced rigid insulation that I will be installing between the firebrick and metal heat shields to further prevent heat loss through the brick chimney. I also have rock wool batt insulation that I will use above the block off plate. Next winter will be the first test with it installed, so I'll report back here or in my old stove install thread on how it works.

Man that looks nice. I need to pull my insert out this summer and do something similar. I'm afraid mine won't look near as good, I'm used to messing with robots, not sheet metal lol

 

[bholler]

Man that looks nice. I need to pull my insert out this summer and do something similar. I'm afraid mine won't look near as good, I'm used to messing with robots, not sheet metal lol

He didn't have an insert he had a prefab fireplace