Insulating Fire Brick and Insulation behind Fire Brick

[Huntindog1]

I will start this new topic just to combine some threads on the subject.

I plan on trying some of this stuff sometime just dont know when.

Has anyone tried to improve efficiencies with theses ideas?


https://www.hearth.com/talk/threads/are-all-fire-bricks-the-same.83203/
https://www.hearth.com/talk/threads/fire-brick-shrinkage.54769/
https://www.hearth.com/talk/threads/ceramic-blanket-on-a-nc-30.74142/#post-1175740

 

[laynes69]

Our furnace which is EPA certified has a 1/4" insulation blanket behind the firebrick on the walls. There's other manufacturers also that use a blanket behind their firebrick. The cleaner burning furnaces have this, but I think it's due to the large fan cooling the firebox. The insulation helps maintain higher temperatures to promote cleaner combustion. For us there's a heat exchanger after the firebox separate from where combustion takes place to extract some heat.

On a stove, those walls are at a much higher temperature than a furnace. I would think at that point the insulation blanket isn't needed to keep firebox temperatures higher. I'm sure some stoves use it, but most don't. Not sure what improvement would be seen from the stove with an blanket behind the brick.

 

[ScotO]

I can't see the benefit of putting insulation BEHIND your firebrick in a woodstove. Isn't the point of burning the wood in the firebox to get the stove itself (including top, rear, and sides) hot and radiate heat outwards? Wouldn't insulating the sides reduce the convection of heat to the outer stove walls? Just my two cents....

 

[corey21]

I can't see the benefit of putting insulation BEHIND your firebrick in a woodstove. Isn't the point of burning the wood in the firebox to get the stove itself (including top, rear, and sides) hot and radiate heat outwards? Wouldn't insulating the sides reduce the convection of heat to the outer stove walls? Just my two cents....

+1 I agree.

 

[laynes69]

I can't see the benefit of putting insulation BEHIND your firebrick in a woodstove. Isn't the point of burning the wood in the firebox to get the stove itself (including top, rear, and sides) hot and radiate heat outwards? Wouldn't insulating the sides reduce the convection of heat to the outer stove walls? Just my two cents....

That's my thought also. There's gotta be a happy medium between heat output and performance.

 

[ScotO]

Now, we did talk before about some stoves having a blanket of thin ceramic-based insulation on top of the baffles, but that wasn't really for insulating purposes.....that was more to seal up drafts where hot gasses could leak around the baffles. On my Napoleon 1900P, the smoke goes up near the top of the stove, mixing with the secondary air under the baffles, and working it's way around the front of the baffles, along the top of the stove housing and out the flue exit. But with the small gaps around the baffles, you can see some leakage of smoke up through that area. I thought about installing a thin piece of insulating blanket (1/4" to 1/2" thick) on top of the baffles to help seal up those small gaps around the edges of the baffles. I imagine the benefit would be small, but it may make for a better secondary flame lightshow. I know I'm overthinking, but I didn't get the handle 'Overkill' for nothing.....

 

[Huntindog1]

I see your point about heat radiating out the sides. One thing I have noticed is most my heat already radiates thru the top and front of the stove.

But it can be a tricky way of looking at things as if the firebox is kept hotter then there is a more efficient burn going on at any one setting that you care to set the intake air at. Plus at the lowest setting alot of stoves the secondaries will go out. If there is a more efficient burn going on then there is more heat to radiate out the top and front of the stove and even the sides as its not going to keep all the heat from radiating out the sides. As one person who posted in another post that its temperature difference that determines how much heat transfer there will be. So simply put, if the stove is burning more efficient the stove is a little hotter and that means temperature difference is greater for greater heat transfer.

Here is a description I found:

Basic Concepts

Heat transfer in engineering consists of the transfer of enthalpy because of a temperature difference. Enthalpy is the name for heat energy, to distinguish it from other sorts, such as kinetic energy, pressure energy, useful work. There has to be a temperature difference, or no heat transfer occurs.
(If we insist on moving enthalpy from a cold body to a hotter one, we will have to do extra work, as in the case of a refrigerator. This invariably involves some other process, such as mechanical work, and cooling by expansion of gases, but within the overall activity heat transfer always goes from the hotter to the cooler.)
The temperature difference is called the driving force. Other things being equal, a greater temperature difference will give a greater rate of heat transfer.

Wes999 said after he did the insulation he could turn his air input all the way down and keep his secondaries burning which translates into the extra BTU's of heat at over night low setting for a all night burns. Maybe not as good as a blaze king getting a 40 hour burn but better than our stoves were getting before. Someone in another post said the blaze kings were using pumice firebricks which are the firebrick that have a higher insulation value to keep more heat in the fire box so the cat can keep active at lower settings/longer burns.

 

[FyreBug]

Mmmmm... The reason the insulation blanket is used in a furnace is you dont want a furnace to radiate heat on the sides but concentrate it in the heat exchanger.

As mentioned, additional insulation on the sides and back would theoretically concentrate more heat at the burn tubes level and possibly up the flue. Thereby doing the opposite of what you are trying to achieve. It may actually reduce your efficiencies (more heat up the flue), affect your EPA rating and since this is considered a firebox modification void all your safety and EPA rating.

If something goes wrong and the house burns down it might disallow your insurance. I dont think it's worth it.

 

[corey21]

Mmmmm... The reason the insulation blanket is used in a furnace is you dont want a furnace to radiate heat on the sides but concentrate it in the heat exchanger.

As mentioned, additional insulation on the sides and back would theoretically concentrate more heat at the burn tubes level and possibly up the flue. Thereby doing the opposite of what you are trying to achieve. It may actually reduce your efficiencies (more heat up the flue), affect your EPA rating and since this is considered a firebox modification void all your safety and EPA rating.

If something goes wrong and the house burns down it might disallow your insurance. I dont think it's worth it.

Very true.

 

[Huntindog1]

There are already guys who have switched to insulating fire bricks and there are stove companies using the insulating fire bricks. Quadrafire stoves are one of them.

The insulation is a cheap way to not have to switch your firebricks. And easily reversible.

But you guys are too late I ordered the insulation this morning on WES999 testimonial for performance improvements and I have to say the technology seems to be backed up by previous designs.

This was only a discussion of the technology no body has to tweak their stoves.

 

[DexterDay]

My stove has angle iron welded into the top to hold the bricks. No extra room for insulation.

Also, the amount of heat vs cleaner burn is trivial. Your probably talking minutes. Not hours of longer burns.

I can turn my 30 down to a 1/2" from closed (where its sitting now/little chilly ). To be able to go the other 1/2'? When the primary already doesn't close all the way, The doghouse air is unregulated, and secondary air is unregulated. So that extra 1/2" I close it, means that one of those 3 already open air spaces is gonna suck (draw) that little bit of extra bit anyways.

I want heat from my stove. A clean burn already happens. Unless its a cold start, or a reload (even reloads dont smoke much). Its already producing no smoke. So if the stove is already burning all the excess gases? Whats left to burn?

Does your stove produce a lot of smoke during normal operation?

 

[Huntindog1]

My stove met emissions just like everyone elses did in a certified lab, just tweaking it a little to see if how much improvement I can get out of it.

We need a forum for new ideas on stove designs and such, alot of us work in engineering for our day jobs. We are always asking the question "What if?".

But by all means if you dont feel comfortable tweaking your stove a little dont do it as its fire your playing with. This is just a discussion is all it is. Exchanging ideas.

 

[begreen]

There is the DIY forum which could be used for modification ideas/questions.