Having a house built - Does this chimney opening look right?

[Snoochers]

I'm having a house built and the goal is to have a STUV 21-125SF in the main living room. My contractor has framed the first floor and the fireplace opening looks like this:

You can see the hole in the wall here where the unit is suppose to go in the first picture. The second picture shows the hole in the ceiling of the cavity for the flue to go up and it shows the exterior wall of the living room and rigid insulation. The flue will go up along this wall until the chimney ends. There isn't a chimney yet but when things are said and done it should look like this:

The part that caught my attention is how there is rigid insulation along the exterior wall above the unit. In other words, it appears the flue will come out of the fireplace and go directly along the exterior wall and not be part of the thermal envelope. The fireplace unit will be part of the thermal envelope of the house, but as soon as the flue starts it will be going up in an uninsulated chimney structure that is essentially "outside".

Does this look right? Is this standard or best practice? I was under the impression that the whole flue should be "inside" the house, but I'm a layman. Any guidance would be appreciated! Sooner the better...!

 

[Sailrmike]

I'm having a house built and the goal is to have a STUV 21-125SF in the main living room. My contractor has framed the first floor and the fireplace opening looks like this:

View attachment 264259

View attachment 264258

You can see the hole in the wall here where the unit is suppose to go in the first picture. The second picture shows the hole in the ceiling of the cavity for the flue to go up and it shows the exterior wall of the living room and rigid insulation. The flue will go up along this wall until the chimney ends. There isn't a chimney yet but when things are said and done it should look like this:

View attachment 264260

The part that caught my attention is how there is rigid insulation along the exterior wall above the unit. In other words, it appears the flue will come out of the fireplace and go directly along the exterior wall and not be part of the thermal envelope. The fireplace unit will be part of the thermal envelope of the house, but as soon as the flue starts it will be going up in an uninsulated chimney structure that is essentially "outside".

Does this look right? Is this standard or best practice? I was under the impression that the whole flue should be "inside" the house, but I'm a layman. Any guidance would be appreciated! Sooner the better...!

I don't know you can have both 1) an exterior chimney, and 2) have that exterior chimney be part of the heated envelope of the home. It would be a lot of wasted heat in my opinion. Are they using an insulated class a chimney pipe inside of the chimney syructure? As long as you have an insulated all fuel pipe in there, I think you'll be good

 

[Snoochers]

I don't know you can have both 1) an exterior chimney, and 2) have that exterior chimney be part of the heated envelope of the home. It would be a lot of wasted heat in my opinion. Are they using an insulated class a chimney pipe inside of the chimney syructure? As long as you have an insulated all fuel pipe in there, I think you'll be good

What do you mean it would be a lost of wasted heat? At least the heat would be inside the home when the fireplace is running instead of out in the cold! Or perhaps I misunderstand?

 

[Sailrmike]

What do you mean it would be a lost of wasted heat? At least the heat would be inside the home when the fireplace is running instead of out in the cold! Or perhaps I misunderstand?

No worries, what I meant to communicate was that if you were to extend the envelope to include the exterior chimney structure, it's that much more volume and exposed surfaces to keep heated all winter long. As currently constructed, the fireplace is within the heated envelope and doesn't have to waste heat into the exterior chimney structure.

 

[Snoochers]

No worries, what I meant to communicate was that if you were to extend the envelope to include the exterior chimney structure, it's that much more volume and exposed surfaces to keep heated all winter long. As currently constructed, the fireplace is within the heated envelope and doesn't have to waste heat into the exterior chimney structure.

Yeah certainly it would be additional square footage and surface area! I'm just worried the flue will be too cold in winter and when I open the door I get a backdraft or trouble getting air going in the right direction.

 

[qwee]

That is usually what is done - the chimney outside the house. Is it the best practice? Not really. Why? The bulk of your chimney's thermal mass is outside of the house. So some of the heat you generate is transmitted to the outer environment. If your wood burner location was centrally placed within the house it would be better, especially since you are in a colder environment (Canada).

 

[Snoochers]

That is usually what is done - the chimney outside the house. Is it the best practice? Not really. Why? The bulk of your chimney's thermal mass is outside of the house. So some of the heat you generate is transmitted to the outer environment. If your wood burner location was centrally placed within the house it would be better, especially since you are in a colder environment (Canada).

The question is then whether it is worth putting the entire flue/chimney inside the thermal envelope

 

[qwee]

Exactly. Say you built this house twice. In one you put the chimney outside and in the other inside. And you keep the internal temperature the same in both houses throughout the cold months. How much more wood will you need to burn in the outside chimney house?

 

[Snoochers]

Exactly. Say you built this house twice. In one you put the chimney outside and in the other inside. And you keep the internal temperature the same in both houses throughout the cold months. How much more wood will you need to burn in the outside chimney?

Yeah good question! Got the answer? Lol.

 

[qwee]

No. But maybe someone else does. Someone who has been in an inside chimney house and an outside chimney house with similar wood burners.

 

[Snoochers]

No. But maybe someone else does. Someone who has been in an inside chimney house and an outside chimney house.

Haha ! Yes that sounds about right. There is also the issue of fireplace draw, which I believe is better if it is all in the envelope.

 

[Sailrmike]

The question is then whether it is worth putting the entire flue/chimney inside the thermal envelope

I would think at this stage of your project, leave as is. But your concerns are quite valid. You could insulate the chimney with Roxul and provide some air exhange vents into the heated envelope. This might be enough to maintain good draft in cold temps.