Installing Stoves and creating cold bridge

Troy McClure

We are builing a pretty airtight house using a HP for heat and a HRVS. We are looking at putting in 2 stoves with external air intake. I spoke with people in Boru and Stovax asking how to do external air intake and the ramifications. They said if on eternal wall to run a pipe straight through the wall, and if on internal wall to run a four inch pipe down through the floor insulation the out to one side. When I ask them about cold bridges they dont think it's an issue. It would seem to be an issue to me looking at this. What do people think?

Also, we are putting one of the stoves in a sitting room that wont get much use realistically speaking. If we didn't put a stove in here, what could we have as a focal point in the room.? We dont want open fires due to the airtightness issue.

A note also - These company's told me that there is no such thing as really room sealed solid fues stoves. This is only for gas. It was described to me as 'best as a bad lot' for airtight house. This goes against what some salesmen have told us.

sydthebeat

my preference for air intakes is always through the floor.

on the cold bridge issue, the ground will always be warmer than the air on those cold days where cold bridges are more significant ie delta T is greater.

Troy McClure

Thanks Syd,
Why is that your preference? Would you insulate around pipe? Is there an issue with same for going straight through external wall behind?

sydthebeat

the reason for it being my preference is the fact that ground is warmer than air... thus reducing the cold bridge...

insulating around the pipe is kind of pointless when your sucking cold air into the pipe.

also i think aesthetically, a ground intake can be neatly hidden under the stove within a featured breast.

sas

Hi Troy,

Going to agree with Syd and add a little more.

First off, you're getting hung up on the wrong thing I suspect. You're concerned about the air intake pipe but you've not mentioned your chimney. Is it masonry because if it is I'd forget all your worries on the intake pipe, that chimney is a great big cold bridge with bells on!

What you were told re room sealed stoves is pretty much true, there are some very good ones but buy and large they are not room sealed 100%.

Pipes going through the floor are less of an issue because as syd has already said, the gound beneath the house effectively insulates it anyway. This is the exact detail I've used in my passive house.

The ideal set up thermally speaking is for your chimney to be outside the insulation body of the house i.e basically you can see the chimney breast on teh outside of your house. That way the only cold bridge is the 4 inch air intake pipe and the 6 inch flue liner where the smoke leaves. The chimney itself is outside the house.
This is damn difficult to execute properly on site. A friend of mine has 2 chimneys in his passive house, 1 external like this, 1 internal with a special build up to minimize the cold bridging effect. If he was doing it again as he says himself the PHI can "go hump" and the external chimney would be inside the house.

Please give us a little more detail on your proposed chimneys etc but as I said earlier you may be getting hung up on the wrong thing.

SAS

Troy McClure

How does this air intake pipe come into the house. I thought it would go down through the floor insulation then go toward the easiest outside wall. Then come upward to the ground on the outside after going under both walls.
Builder says this would be a problem as rain water or debris would interfere with it by getting into it. He thinks It would have to come up through the cavity, after coming back up through floor insulation then turn again to go out through the outer relief. This would allow the vent to be put on the wall outside. The cavity is 200mm full fill bonded bead. A 4 inch pipe coming up through your cavity has got to effect the efficiency of insulation around this area, no?
Can people who have experience of this tell me how they done this?. I have one stove in an inner wall and another one on an outside wall. HELP

Do-more

Have you considered a flueless fireplace burning gel or bio ethanol?

Troy McClure

Stoves are wood burning. Dont have the budget for specialist items am afraid.

Syd you seem to have done this before, how did you treat the air intake pipe exiting the house and on the outside?

Do-more

Troy McClure wrote: »

Stoves are wood burning. Dont have the budget for specialist items am afraid.

If you go with a flueless fireplace you have no need to install a chimney or an air feed (just be sure your MHRV is working!) so they will cost significantly less to install than your wood burning stoves.

Granted they don't appeal to everyone on appearance grounds or as you won't have the smell of burning wood or turf, but from a cost perspective there is nothing to be said against them.

Troy McClure

We are already committed to this route. But we really need an answer to the above..

glenkeo

Hi Troy

Just finished a self build in Nov 2010 I spent a lot of time on getting it airtight and have MHRV and a stove with outside air. I used a twin flue which came has a kit for whatever height you need and is made up of a kind of rectangle pumas stone which has one large hole that a standard flue pot fits in with space for extra insulation around it and a second smaller hole that takes air down to floor level. Then I cut a 4” hole in to the air chamber and attached a 4” pipe to that and then attached the other end to the stove it has a (4” adapter on the bottom).
I had a fire on all last winter and have to say I had no problems. The stove is not completely airtight, there was very little choice on suitable stoves at the time , I went for one off the boru (I hope it is ok to mention the name) in the end I have had no problem with draw on the fire which I was concerned about has there is a lot of debate about this on other posts I even have a air out vent just above the stove. Not sure if this helps.

Troy McClure

glenkeo wrote: »

Hi Troy

Just finished a self build in Nov 2010 I spent a lot of time on getting it airtight and have MHRV and a stove with outside air. I used a twin flue which came has a kit for whatever height you need and is made up of a kind of rectangle pumas stone which has one large hole that a standard flue pot fits in with space for extra insulation around it and a second smaller hole that takes air down to floor level. Then I cut a 4” hole in to the air chamber and attached a 4” pipe to that and then attached the other end to the stove it has a (4” adapter on the bottom).
I had a fire on all last winter and have to say I had no problems. The stove is not completely airtight, there was very little choice on suitable stoves at the time , I went for one off the boru (I hope it is ok to mention the name) in the end I have had no problem with draw on the fire which I was concerned about has there is a lot of debate about this on other posts I even have a air out vent just above the stove. Not sure if this helps.

Thanks Glenkeo
Was that a system you came up wit yourself or was it something you bought for it? I know of one company starting with 'S' that do chimney systems, but they seemed expensive and a bit unneccessary to me.
I dont think the stoves are any better now and the range of stoves with external air intake could be better, but I was hoping more people, especially builders, would be able to give me some feedback on this.

glenkeo

Hi troy
hi troy
I bought a shield system all in I don’t think it was much more expensive than normal flue system, it came with lintels and a starter cap (not sure that is the right term) and all the flue liners, sealer, insulation, top flue pot and a second smaller pot for air, Copeing, a lead apron that sits in the coping that is filled with concrete to seal it. There is also a collar that your stove flue fits in to. Makes fitting stove a lot hander. The only negative I found with it is you are limited to space between the wall and back of your stove (because of space between two flues) unless you have flue out the back and then up to flue starter, I would have liked to have the flue out the top but would have need a bend and a lot of space above stove (Bit hard to explain here). Has the air comes from above roof level there is no hassle with it getting blocked and it is very well insulted
Has for the range of stove I rang ever company and they were all in development, I have seen a brocher lately for a Stanley with external air I liked the look of it but did not look too much at spec.