Getting heat out of the fireplace

[Fried Chicken]

I've been told adding an air source can make a significant difference. A friend of mine did this by literally boring holes through the floor in front of his fireplace & he swears by it

This works: the fireplace pulls outside air instead of inside air and radiates heat out.

I built a Rumford designed fireplace from I think about 1790. It has a shallow back wall revealing a large area to reflect heat out. It also has a full width throat with a smoke shelf behind and an adjustable flap to help prevent downdraught and also to stop heat escaping if fully closed when perhaps you are using other heat sources
My old fashioned builder gave me an earful saying he had never seen anything like it and it would never work, but in the Winter I caught him and his mate warming themselves when they should have been on the roof tiling! “ Well I never would have believed it!” They said!

He clearly wasn't old fashioned enough!


I did some reading about fireplace inserts, and maybe I need to overcome my biases. They achieve efficiencies of up to 80% where an open fireplace is happy to get 20%

https://forestry.com/best/best-wood-burning-fireplace-inserts-of-2024/

That said, I don't live somewhere cold so heating needs are minimal. I wish I could burn firewood inlieu of an air conditioner.

 

[Hermio]

I've done a bit more research and slept on the thought.

I don't like the idea of an insert when there's already a perfectly good fireplace. It's a very space inefficient solution.

I do like the idea of glass doors with a blower/heat exchanger of some sort. Unfortunately the only solutions I've find (like this one) similar to the inserts throw a lot of otherwise usable space away. It also looks like a nightmare to clean.

I found a product that kind of looks like it might achieve this

That is similar to what we had. I am a bit shocked by the price, though.

 

[Hermio]

I've been told adding an air source can make a significant difference. A friend of mine did this by literally boring holes through the floor in front of his fireplace & he swears by it

No need to do that. The cold air still needs to be heated up to the firebox temperature whether it comes from room air or a special duct. It cancels out.

 

[Hermio]

I built a Rumford designed fireplace from I think about 1790. It has a shallow back wall revealing a large area to reflect heat out. It also has a full width throat with a smoke shelf behind and an adjustable flap to help prevent downdraught and also to stop heat escaping if fully closed when perhaps you are using other heat sources
My old fashioned builder gave me an earful saying he had never seen anything like it and it would never work, but in the Winter I caught him and his mate warming themselves when they should have been on the roof tiling! “ Well I never would have believed it!” They said!

I also put two four inch diameter pipes feeding air from outside to the sides of the fireplace so the air was not pulled under the doors or through gaps in windows
I put a length of bar from the bottom of the flap over the throat so that I could adjust it from outside with a screw thread.
A pair of mesh doors finished the job over 40 years ago so that it could be safely left unattended or the room shielded if it became too hot

https://images.app.goo.gl/2pxecQnbbyEogX7v6

The Rumford style is much more efficient than most modern designs. The outside air makes no difference though; it reduces the flame temperature a bit.

 

[Hermio]

It is a hot as my wood stoves, an Aarrow and a Danish Aduro and has never smoked even when lighting. Behind the smoke shelf I installed a hinged metal door which can be opened and the chimney swept with the throat flap firmly shut and the soot going outside

With a masonry heat exchanging fireplace such as Tulikivi, you would not get any soot. But these days they usually go for more than $20,000 installed cost.

 

[Hermio]

This works: the fireplace pulls outside air instead of inside air and radiates heat out.

He clearly wasn't old fashioned enough!


I did some reading about fireplace inserts, and maybe I need to overcome my biases. They achieve efficiencies of up to 80% where an open fireplace is happy to get 20%

https://forestry.com/best/best-wood-burning-fireplace-inserts-of-2024/

That said, I don't live somewhere cold so heating needs are minimal. I wish I could burn firewood inlieu of an air conditioner.

Woodstoves and inserts can be efficient if they are allowed to burn the wood completely with no CO or soot or creosote formation. That means burning hot with a small excess of oxygen. But very few people would operate them that way, as under such conditions, the metal will actually glow red hot and the heat output would drive people out of the room. In the real world, people operate such stove with a slow, smoldering burn, which creates a lot of crap in the chimney and reduces efficiency to maybe 30-50%. The Euro style heat storage fireplaces get maybe 85% efficiency by always burning hot and fast but storing the heat in the stone. I have had one in my house for 29 years, burning about 6 cords per year, and there is no creosote in my chimney. I have never had to clean it. I just have to remove the ash from the pit and the internal channels of the unit once per year.

 

[Fried Chicken]

Woodstoves and inserts can be efficient if they are allowed to burn the wood completely with no CO or soot or creosote formation. That means burning hot with a small excess of oxygen. But very few people would operate them that way, as under such conditions, the metal will actually glow red hot and the heat output would drive people out of the room. In the real world, people operate such stove with a slow, smoldering burn, which creates a lot of crap in the chimney and reduces efficiency to maybe 30-50%. The Euro style heat storage fireplaces get maybe 85% efficiency by always burning hot and fast but storing the heat in the stone. I have had one in my house for 29 years, burning about 6 cords per year, and there is no creosote in my chimney. I have never had to clean it. I just have to remove the ash from the pit and the internal channels of the unit once per year.

I'm looking at an insert right now, used, but I could have it installed.
Seller says the blower is broken, so I'd have to look into fixing it. Unfortunately parts are no longer available (Country Flame brand). Are these any good?

 

[Fried Chicken]

No need to do that. The cold air still needs to be heated up to the firebox temperature whether it comes from room air or a special duct. It cancels out.

It's not a question of the temperature of the air being burned. If you pull air in from the outside with a dedicated duct, you're not pulling air into the house via a vacuum

 

[sean donato]

Woodstoves and inserts can be efficient if they are allowed to burn the wood completely with no CO or soot or creosote formation. That means burning hot with a small excess of oxygen. But very few people would operate them that way, as under such conditions, the metal will actually glow red hot and the heat output would drive people out of the room. In the real world, people operate such stove with a slow, smoldering burn, which creates a lot of crap in the chimney and reduces efficiency to maybe 30-50%. The Euro style heat storage fireplaces get maybe 85% efficiency by always burning hot and fast but storing the heat in the stone. I have had one in my house for 29 years, burning about 6 cords per year, and there is no creosote in my chimney. I have never had to clean it. I just have to remove the ash from the pit and the internal channels of the unit once per year.

your cart blanc statement about efficiency and burn rate is bs. Any even semi modern listed furnace will be very efficient even when not burning wide open, and not produce creosote in the chimney. Reburn chambers, secondary air injection, and cats have improved output and efficiency greatly over smoke dragons of yesteryear.

 

[Hermio]

I'm looking at an insert right now, used, but I could have it installed.
Seller says the blower is broken, so I'd have to look into fixing it. Unfortunately parts are no longer available (Country Flame brand). Are these any good?

I don't know.

 

[Hermio]

It's not a question of the temperature of the air being burned. If you pull air in from the outside with a dedicated duct, you're not pulling air into the house via a vacuum

One way or another, the combustion air has to be heated. It will take the same amount of heat away from the fire if added directly as it will if it goes through the house, so that theoretically cancels the benefit. The folks at Tulikivi researched this and found that letting cold air go directly to the fire actually reduced combustion efficiency, so the end result was actually a slight heat loss. They do not recommend an outside air duct going directly into their fireplaces.

 

[Hermio]

your cart blanc statement about efficiency and burn rate is bs. Any even semi modern listed furnace will be very efficient even when not burning wide open, and not produce creosote in the chimney. Reburn chambers, secondary air injection, and cats have improved output and efficiency greatly over smoke dragons of yesteryear.

I am aware that the features you mention improve efficiency. But it is simply a fact that a smoldering fire is less efficient than one which achieves complete combustion. The catalyst may prevent creosote but it will likely get clogged at some point. Would you trust such a system to go 20 years or more with no chimney cleaning?

 

[sean donato]

I am aware that the features you mention improve efficiency. But it is simply a fact that a smoldering fire is less efficient than one which achieves complete combustion. The catalyst may prevent creosote but it will likely get clogged at some point. Would you trust such a system to go 20 years or more with no chimney cleaning?

Yes, with proper care, use and seasoned wood there's zero reason a secondary burn system or cat stove will give issues in a 20 year period. The cats will eventually use up the precious metals used so naturally they will eventually need replaced. Secondary burn systems are self contained and have no real wear parts. I have the latter. So long as I keep pipe outlet temps above 300* there's virtually zero build up in a years time. Heated secondary air combustion burns off any soot/ unburned gassed in the case of my stove. Start up smoke is minimal, and not any worse then a rocket mass stove till it gets some heat in it.
Most people's issues are lack of knowledge of how to use the systems, improper care and wet wood. Everyone want to bag on the systems as junk, but when pointed out they were using wet wood, took a wire brush to the cat or choked it down to the point secondary combustion can't take place, they get all butt sore and defensive. Doesn't make it any less true. Certainly there are old stoves, fireplaces and furnaces that will burn like crap not running wide open, but that's been a load of bs for many years now.