Decorative brick liner: More efficent, or less, or no difference?

[tubbster]

The fake bricks are lining the firebox on three sides. They seem to be made out of some ceramic foam. Are they adiabatic enough to change efficiencies?

 

[R&D Guy]

Yes, ceramic firebacks make the appliance less efficient because it helps to insulate the firebox. In general you want the thinnest amount of material (sheet metal only) between the fire and the combustion chamber.

 

[Fire Bug]

The fake bricks are lining the firebox on three sides. They seem to be made out of some ceramic foam. Are they adiabatic enough to change efficiencies?

Hi Tubbster,
I have the brick kit installed on my Jotul GF 600 DV Firelight Propane stove and was wondering the samething after I bought the stove.
I could put my hand on the side of the unit and it will only be warm to the touch, all the heat comes from the grate on top of the unit and especially from the front of the ceramic glass.
Even though the sides of the stove might not heat up, I am wondering if these brick kits acting as an insulator help direct and push the heat out towards the front and through the glass.
I have a Heat & Glow FB Grand Fireplace Insert with the total ceramic firebox and the idea of this is to insulate the firebox and push the heat out the front of the glass. Of course, this is a fireplace insert not a freestanding stove, so you want the heat to go out the front and not through the metal sides of the insert into your existing firebox.
I can believe a quality company like Jotul would make a brick kit that would greatly cut down on the units overall efficency by having this kit istalled as an option, but who knows!
Thanks,
John, (Firebug)

 

[tubbster]

The brick sides and back were a $70 option that I threw in with the order. They are installed now, I really think it makes the stove look much better. I do wonder how much the efficiency has changed however. If it was only maybe 1%, no problem, they stay. If it was 10%, they would have to go.

I am always trying to optimize everything with the stove to get the most out of my $1.74/ therm! The exhaust is way hotter than it needs to be IMHO. It is so hot that the outside pipe of the DV is hot to touch. And that is cooled by the incoming air!

I do realize that most people buy gas stoves for looks/comfort. But if I am burning gas, no reason not to get all I can out of it. Seems to me they could get quite a bit more efficient before they have to give up looks. IIRC, the exhaust has to stay above 300 or so to negate condensing. I have yet to measure the EGT, but I am guessing it is more than double that! Not much I can do about it anyway.

 

[Fire Bug]

The brick sides and back were a $70 option that I threw in with the order. They are installed now, I really think it makes the stove look much better. I do wonder how much the efficiency has changed however. If it was only maybe 1%, no problem, they stay. If it was 10%, they would have to go.

I am always trying to optimize everything with the stove to get the most out of my $1.74/ therm! The exhaust is way hotter than it needs to be IMHO. It is so hot that the outside pipe of the DV is hot to touch. And that is cooled by the incoming air!

I do realize that most people buy gas stoves for looks/comfort. But if I am burning gas, no reason not to get all I can out of it. Seems to me they could get quite a bit more efficient before they have to give up looks. IIRC, the exhaust has to stay above 300 or so to negate condensing. I have yet to measure the EGT, but I am guessing it is more than double that! Not much I can do about it anyway.

Hi Again Tubbster,
I agree with you about the looks of the stoves with the brick kits, I think they do look better.
Woodstock Stove Co. makes excellent wood and gas stoves out of soapstone but they do not offer a blower option for neither.
The soapstone maybe effective for holding and releasing heat gradually on the wood stoves but I have to believe that it is purely decorative for the gas stoves especially when they are on a thermostat.
Woodstock claims that all of their heat produced by the gas stoves is pushed out the front of the ceramic glass and no blower is needed. I believe that the decorative brick panels do the same thing but I may be mistaken.
Thanks,
John,(Firebug)

 

[jtp10181]

Some units we sell actually have an entire molded firebox made of a fiber ceramic material. This stuff helps reflect heat back into the firebox and out through the glass. You can get much more noticeable heat out of them without running a fan (compared to a steel unit the same size).

 

[Fire Bug]

Some units we sell actually have an entire molded firebox made of a fiber ceramic material. This stuff helps reflect heat back into the firebox and out through the glass. You can get much more noticeable heat out of them without running a fan (compared to a steel unit the same size).

Now your talking "Turkey With A Gobbler". I believe the "FB,(Firebrick Series), fireplaces and inserts and even possibly the Tiarra II gas stove has these molded ceramic fireboxes for the reason JTP just stated. I also believe Quadrafire is getting into this design.
Thats why I have stated that my Jotul GF Firelight DV II propane stove might being utilizing the same priciple with their brick kit. Maybee the cast iron sides of the stove don't heat up because of the insulating characteristics of the ceramic brick liner kit but I think it absorbs the heat and directs it out of the top and front of the unit.

Thanks,
John

 

[Inside Guy]

There's just too many variables involved to say that adding optional components such as blowers and brick kits will change a fireplace's efficiencies.

 

[R&D Guy]

Maybee the cast iron sides of the stove don't heat up because of the insulating characteristics of the ceramic brick liner kit but I think it absorbs the heat and directs it out of the top and front of the unit.

Thanks,
John

I've added ceramic liners to the fireplaces I've designed to get closer clearances to combustibles. That means they end up being required when you are done. So at least for the designs I've worked on I can tell you adding ceramic liners insulated the firebox more. I quite sure that's why jtp noticed more heat coming out the glass - because there is. By insulating 3 walls of the firebox, less heat can escape out of the firebox, so the air temp inside the firebox increases, and the glass and flue temps increase. This might not be all bad for a fireplace, especially if its installed in a dog house. Smaller enclosure's seem to be high on the priority list.

But again, looking back at some of the projects I've worked on, adding ceramic liners decreased the enclosure temperatures including the combustibles touching the top of the fireplace. The side effect is hotter glass temps and hotter flue temps. Flue temps increase by a good 60° which can be a problem if your temps are close to the limit where your pipe passes through the wall, and if you are using temperd glass it can push you over the limit.

Same flue temp increases with inserts too, but the components under the appliance get quite a bit warmer since the unit can't breath like it use to. Again, this could be a good thing.

I've never tested the differences on a free-standing stove because if the surface temps are over the limit there are real easy ways to exempt that area from the test, but I can't image that it would behave differently which is NOT a good thing for a free-standing unit. Since each side of the firebox radiates and convects heat into the room it would be a negative thing to reduce that and do anything that increases the flue temps. I just don't see any positive trade offs efficiency wise with a free standing unit.

Make Sence?

 

[R&D Guy]

IMO Fire Bug has had the best suggestion so far, and I think it's something Tubbster already has working for him which is to restrict the flow rate in the flue as much as possible. Listening to tubbsters problems it sounds like his flue is already operating as slow as possible and even a little slower than it should. This will give you the max firebox temps. One thing to keep in mind is that by doing this you have improperly installed the unit which I'm sure the install manual warns what can happen if you do that.

Another nice trick to increase your AFUE is have a lot of DV flue pipe venting your fireplace. I've found vertical sections of pipe to add the most points since the exchange is uniform. In general what this does is it allows your hot flue gases to pre-heat the combustion air reducing the amount of heat at the flue termination while increasing firebox temps. This type of countercurrent heat exchange is also the most efficient form; as the combustion gas travels closer to the firebox the inner flue pipe gets hotter and hotter exchanging more heat energy into the combustion air.