make up air for a wood burning insert?

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

just clint

New Member
Sep 21, 2022
5
canada
Hi everyone , I was looking for some input into makeup air.
When shopping for an insert for our old open fireplace, I noted that many of the built in high efficiency wood stoves for new construction had fresh air intake plumbed right into them.
I chose a 24 inch Supreme fusion model. We installed it without the surround to try it out. It made beautiful rolling flames and put out good heat from the glass front.
I have a couple of challenges...
1. When you open the door it bellows smoke into the house. To ty to solve this we open a patio door across the room, which helps with the smoke but cools the large room down.
Now to clarify, I only open the door when the burn has come down and is ready for more wood to be added, but I get the smoke. If i let it burn right down to embers and open the patio door is best results, but the fireplace has quit giving heat and we still get smoke.
2. The 2 fans that flank each side of the fireplace blow decent heat out with the face cover off, but as soon as you put the cover on- closing off the chamber created between the stove box and the old masonry fireplace it cannot seem to move air.
The fans are blowing from the heated space creating a vacuum in the space.
The old fireplace had an ash flue going down to capture the ash with a door to open in the basement so you could remove the ash and then close the door again.
My question is this.
Could you run afresh air line from the exterior of the home and connect it to the ash flue?
this would provide fresh air for combustion to the chamber which would feed the damper control at the top of the stove, and it might allow the 2 fans to push out more hot air as it draws air in through the fresh air intake.
Thoughts?
 

stoveliker

Minister of Fire
Nov 17, 2019
6,229
Long Island NY
I can't help with the air issue, but the smoke roll out might be related to the chimney. How tall is it? And is it the correct cross section for this insert?
 

Ashful

Minister of Fire
Mar 7, 2012
17,602
Philadelphia
Aside from a too-short chimney, smoke roll-out is often an indicator that an outside air kit is required. The standard test for this is to open a door or window in the room with the stove, a minute or two prior to opening the stove door, to let pressures equalize. If this resolves your smoke roll-out, then an outside air supply is likely warranted.

If your stove has provisions to connect one, then bringing fresh air in thru the old ash cleanout, if that is indeed what that is would seem to make sense. However, we need to clarify two things:

1. Is it actually an ash clean-out, as you assume, or is it a fresh air intake for the fireplace. It was quite common to add fresh air intakes to the floor of open fireplaces, we had them on both the 1950's and 1980's fireplaces in the house where I grew up.

2. If it is not a fresh air intake, and indeed an ash clean-out door, can fresh air be brought into it legally? I say this because modifications to fireplaces must not make the fireplace fail code if converted back to an open fireplace, most often seen in the form of hearth extensions atop flooring. but also applicable to other modifications.
 

stoveliker

Minister of Fire
Nov 17, 2019
6,229
Long Island NY
I agree with Ashful; the chimney seems to be of decent length. And I had not seen the remark that when you open a patio door, the smoke roll out stops.
This indeed suggests an outside air supply might be needed.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,346
South Puget Sound, WA
It does sound like a negative pressure issue. This can be caused by exhaust fans, furnaces, clothes dryers, etc. It can also be caused by air leakage on the 2nd floor. Prime suspects in this case are leaky attic doors or vents or leaky upstairs windows.

One thing to check is to make sure the flue is clean and that the cap is not causing restriction. This can happen if the cap has a screen that is starting to plug up. I looked at the manual and it doesn't appear that the Supreme Fusion has an outside air connection option so I'm not sure how effective using the ash door would be, but it's worth a try. A basic test would be to open the ash pit door in the fireplace and open the ash pit cleanout door to see if that improves things. It may not because the circulating chamber floor may block off the ash pit door hole.

If the house is exceptionally tight, another possible solution is a fresh air supply via an HRV that balances room pressure with fresh incoming air that is preheated with outgoing exhaust air.
 

just clint

New Member
Sep 21, 2022
5
canada
Aside from a too-short chimney, smoke roll-out is often an indicator that an outside air kit is required. The standard test for this is to open a door or window in the room with the stove, a minute or two prior to opening the stove door, to let pressures equalize. If this resolves your smoke roll-out, then an outside air supply is likely warranted.

If your stove has provisions to connect one, then bringing fresh air in thru the old ash cleanout, if that is indeed what that is would seem to make sense. However, we need to clarify two things:

1. Is it actually an ash clean-out, as you assume, or is it a fresh air intake for the fireplace. It was quite common to add fresh air intakes to the floor of open fireplaces, we had them on both the 1950's and 1980's fireplaces in the house where I grew up.

2. If it is not a fresh air intake, and indeed an ash clean-out door, can fresh air be brought into it legally? I say this because modifications to fireplaces must not make the fireplace fail code if converted back to an open fireplace, most often seen in the form of hearth extensions atop flooring. but also applicable to other modifications.
Hi Ashful, thanks for your comments. The ash cleanout has a door, currently full of ashes. I was going to run a sleeve in it to the outside with a power controlled valve. The combustion air intake for the fireplace is on the top toward the front, but I was thinking to just supply air to the cavity between the sealed burner box and the old fireplace cavity now closed in by the faceplate. My thought is the fireplace intake, and fans would draw air as needed. I was also thinking that I would try to seal up this cavity from the chimney so it does not draw air from the space between the chimney flue and the liner.

fusion image.JPG
 

stoveliker

Minister of Fire
Nov 17, 2019
6,229
Long Island NY
The last thought is a good one; it's called a block off plate. It'll make a big difference in heat output.

The former, though, I'm not sure about. Supplying cold outside air not directly pipes into the firebox, but to the place where the fans also draw from (because the cold air would have to cross the jacket where the fans are at work) means you'll be blowing more cold air into the room?

Maybe I'm mistaken as to the design of this thing.
 

Ashful

Minister of Fire
Mar 7, 2012
17,602
Philadelphia
Agreed with stoveliker on all points!

But it’d be good to get @bholler’s take on this, he’s an actual chimney professional. Most of the rest of us have just spent enough time here to learn some of what’s right from him, or a few of the other pros that have here.
 
  • Like
Reactions: stoveliker

just clint

New Member
Sep 21, 2022
5
canada
The last thought is a good one; it's called a block off plate. It'll make a big difference in heat output.

The former, though, I'm not sure about. Supplying cold outside air not directly pipes into the firebox, but to the place where the fans also draw from (because the cold air would have to cross the jacket where the fans are at work) means you'll be blowing more cold air into the room?

Maybe I'm mistaken as to the design of this thing.
Thanks for the block off plate info, I will look that up.
I agree on the cold air coming in, and wondered if the makeup air coming in should run through an HRV so it is not too cold. The cold air intake line would have to be about 30 ft long to get to the outside, and would travel through the heated basement, so not sure if that would make a difference or not. To make sure it didn't sweat, or cool off the basement, I was thinking I would have the intake line insulated so the inside air wouldn't warm it up much anyway- maybe coming through a HRV might be wise.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
30,185
central pa
Thanks for the block off plate info, I will look that up.
I agree on the cold air coming in, and wondered if the makeup air coming in should run through an HRV so it is not too cold. The cold air intake line would have to be about 30 ft long to get to the outside, and would travel through the heated basement, so not sure if that would make a difference or not. To make sure it didn't sweat, or cool off the basement, I was thinking I would have the intake line insulated so the inside air wouldn't warm it up much anyway- maybe coming through a HRV might be wise.
Pulling makeup air through 30' of pipe probably isn't going to work very well. Just too much resistance
 
  • Like
Reactions: stoveliker

stoveliker

Minister of Fire
Nov 17, 2019
6,229
Long Island NY
In this case, why not install an hrv just anywhere (same floor or lower floor, I'd say) to equilibrate the pressure of the home (alleviate the underpressure of the room), and install a block off plate..

Easier, more likely to be effective.
 

begreen

Mooderator
Staff member
Nov 18, 2005
96,346
South Puget Sound, WA
Yes, agreed and suggested that option. This insert does not lend itself to an outside air connection for the reasons I explained previously.