chimney downdraft

[HoosierMark]

I have a new house and had a stainless steel double wall chimney put in from the basement thru the first floor and out the roof. I find that I have a back draft on the chimney. The stove installer thinks it is a result of the house being too tight. I foamed the walls an inch and then batts of insulation. I find that when I open the stove door I feel a draft coming in. If I open a window near the stove for a few minutes, the draft does reverse itself. If I do not do this the smoke comes out the cold air inlet for the stove until it gots hot enough to go up the chimney. Opening the window first is not a big deal but I am concerned that when the stove cools, I will end up with the smoke entering the house rather then exiting thru the chimney.
My installer mentioned an outside air supply for the stove. The stove is a Vermont Castings Intrepid II. I am contemplating putting a pipe from the outside and attaching it to the stove air intake but do not have a plan or design yet.

Comments, thoughts, etc?

 

[kd3pc]

in the old days, we would start the chimney drawing with a roll of newspaper or kindling on fire and hold up well in to the chimney, not sure if you can get in to the stove safely, long enough to do this.

Check the damper, else who ever designed the system needs to look at it.

 

[danski0224]

If you can still breathe in the house, it isn't too tight.

There is something else acting as a chimney, causing negative pressure in the home.

 

[HoosierMark]

I am old school and crumbled up several pieces of newspaper, then lit them. The draft is such that it pushed the smoke out the fresh air vent. It is a simple pipe up thru the roof that is about 4 feet high. I know it may need to be higher but I get the draft if it is windy or still. I plan to ask them to try putting a simple piece of pipe up another 3-4 feet as a temporary measure to see if that changes the draw.

 

[HoosierMark]

Installer suggested it might be from the dryer pushing air out and it not being replaced. Also there is a whole house fan at the top of the stairs to the second floor with a plastic louver that probably leaks air. There are doors at both the top first floor stair from the basement and the top of the stairs to the second floor.

 

[danski0224]

Doubtful it is the dryer.

Whole house fan is certainly a culprit. So are any can lights in the ceiling adjoining the attic.

If they set it up without verifying draft, sign of a poor install.

 

[rburke65]

I have had my wood burner for 30 years and before I strike the match, I crack the sliding door 2". It starts to draft in 15 seconds and I close the door. I do use newspaper strips to start the wood and it heats the flue quickly.

 

[TractorJeff]

I agree that you need to heat the chimney to get the draw you require. Any leak in the house will increase the draw up the chimney if the chimney is heated. I live in a leaky house and if the insulated chimney is cold, it won't draw till it heats up. If it is really cold outside and the furnace is on so the house is warm, it will usually draw if the fire hasn't been out to long as it is sucking heat out of the house. My chimney is only 2 feet higher than the peak of the house.
Also if I had a new house that was really tight, then I would definitely figure out a way to bring in outside air to the Stove air Intake so as not to create a draft through the house.

 

[backintheday]

I have the same insulation and issue as you. I plan to install a heat recovery ventilator I also think the chimney isn't tall enough. I have a 7/12 pitch, I think there is an issue with air pressure and the pitch, when the wind directly hits the side of the roof with the chimney I get a down draft. The chimney is about 18'' above the ridge and over 10' away. I'm going to install another 2' and see if that fixes it.

 

[nehog]

...
My installer mentioned an outside air supply for the stove. The stove is a Vermont Castings Intrepid II. I am contemplating putting a pipe from the outside and attaching it to the stove air intake but do not have a plan or design yet...

I have a Vermont Castings Vigilant. One of the smartest things I did was designed and built an outside air intake for it. Before we did this, we had this flow of cold air across the living room floor that made the room very uncomfortable.

It works well, but that pipe is wicked cold when the stove is burning! I guess that proves it works.

 

[MagKarl]

Newer homes that are more air tight than they used to be can cause this. Especially if you have any equipment exhausting such as kitchen/bath fans, or the dryer as mentioned. Every bit of air exhausted needs to be replaced by coming back in wherever it can. Do you have a make up air duct that goes outside? Any chance that's blocked?

I have an outside air kit on my stove but I have to make sure the kitchen hood is not on when I first light a fire in the cold stove or I'll get smoke back into the room.

 

[yeldogt]

In a tight house running the dryer will create a negative pressure. So will kitchen and bath fans as well as open combustion water heaters and furnaces. Can also get a stack effect if there are leaks to a vented attic.

A spray foamed house needs make up air. Normally they have sealed combustion appliances and a fresh air inlet.

A heat recovery ventilator does not provide make up air -- they provide fresh air.


I'm in the mid atlantic -- so my make up air goes through a whole house dehumidifier. I keep the house slightly pressurized.

 

[Jackfre]

I would say your stove dealer is correct and your tests prove it. Negative pressures in homes are quite common and one of the biggest reasons for having sealed combustion direct vent heating appliances. Do put the outside air kit on the stove. That should handle the stove, but the negative pressure overall will persist. I am all about improving the efficiency of my home, but would rather pay for a bit more fuel than to be "stewing in my own juices" all the time.

I ran into this problem on a lot of homes in my business. It would especially show on oil fired appliances because you could smell the oil backdraft. Look at the number of vents coming out of the house. Laundry, fart fans, range, etc. how many allow air in? If you heat with gas and have a negative pressure, make sure your CO detectors are good

 

[theoldwizard1]

My installer mentioned an outside air supply for the stove. The stove is a Vermont Castings Intrepid II. I am contemplating putting a pipe from the outside and attaching it to the stove air intake but do not have a plan or design yet.

Yep !

The real experts are at www.Hearth.com

 

[HoosierMark]

To follow up. I have geo thermal heat. The bathroom fan(s) are on maybe once a week for five minutes or very seldom. Only air expelled is the gas dryer. As mentioned, at the top of the stairs to the attic is the whole house fan with plastic louvers and the door to the attic area. I am thinking that the air loss is due to heat rising and escaping thru the louvers or when the dryer is running as all is sealed. I can shut off two rooms in the basement where the stove is and I am going to check chimney for amount of down draft in this scenario since there will not be any leaks. I need to be there a while to open a window to equalize air before I observe stove draft. Stay tuned.

 

[big.jim]

in the uk by law for a solid fuel appliance you have to have an outside air source and a co detector fitted

 

[rburke65]

So how large of an outside air source does one need for a wood burner. Metal pipe? A piece of PVC through the wall? What? My outside wall is only 3' away from the bimetallic controlled damper of my wood burner. Would 1 1/2" PVC pipe do it? How do I keep the mice out?

 

[nehog]

So how large of an outside air source does one need for a wood burner. Metal pipe? A piece of PVC through the wall? What? My outside wall is only 3' away from the bimetallic controlled damper of my wood burner. Would 1 1/2" PVC pipe do it? How do I keep the mice out?

My installation uses 3" aluminum pipe (I didn't want plastic). Seems to deliver enough air. I based that size on the size of the air intake on the stove.

 

[big.jim]

we use pre built vents ,core drill a hole and fit sleeve ,baffle and draught cowl , google manthorpe core drill vent

 

[sms1974]

I have the same insulation and issue as you. I plan to install a heat recovery ventilator I also think the chimney isn't tall enough. I have a 7/12 pitch, I think there is an issue with air pressure and the pitch, when the wind directly hits the side of the roof with the chimney I get a down draft. The chimney is about 18'' above the ridge and over 10' away. I'm going to install another 2' and see if that fixes it.

BINGO!!! we have a winner!!!

insulation isn't the culprit, older homes even with great R value of insulation, had more air infiltration ( loose construction ) a house that's been spray foamed is going to have very little air infiltration hence the need for mechanical ventilation. I've yet to see a spay foamed house that didn't need mechanical ventilation.

the air going up the chimney, out a bath fan, recessed lights, ect. has to be replaced. hence the back draft down the chimney. the easy answer is a form of make up air vent. this can be as simple as a barometric damper on a pipe from outside or a heat recovery ventilator. the benefit of the heat recovery ventilator is being able to slightly pressurize the house this prevents the cold drafts you sometimes feel around doors and windows. some of the modern controls can actually vary the amount of air brought in depending on what is being exhausted.