Poor draft or negative pressure issues?

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neverstop

Member
Oct 11, 2020
135
new hampshire
Unfortunately this is going to be a long post so below is the quick summary.

TL;DR - New EPA stove installed with 6" SS liner. I get smoke escaping from the stove when I open the door, and when not in use there is a "smoke" smell in the room with the stove. Previous Vermont Castings Vigilant in same chimney without a liner never exhibited the smoke escaping from the stove with the door open issue, and the "smoke" smell with that stove was minimal. I don't know if this is solely a negative pressure issue or if I have poor draft.
I had a new Hearthstone Shelburne (EPA/Cat) stove installed on the main floor of my house and with it a 6" SS liner (non-insulated). It was installed in an already existing exterior masonry chimney with a rear flue exit. The previous stove was a 1977 Vermont Castings Vigilant that was venting directly into the masonry chimney via a rear exit. Chimney height about the flue is 15+ feet. I've only had 2 burn in fires to force the moisture out of the stove, but with each fire I've experienced smoke escaping from the firebox when I open the door. Additionally, when not in use I am getting a strong "smoke" smell from the stove/flue pipe. With the previous stove I got a slight "smoke" smell when not in use. Outdoor temps were probably in the low 40's/50's the 2 times I attempted the fires, and the oil burner was firing or had been firing and I also believe the clothes dryer was in use.

I opened the door as slowly as possible and smoke still escaped. It usually happens when the door is cracked open 2". Prior to that I can see smoke rolling on itself at the top of the firebox near where the baffle is. I'm surprised by how small the opening is in front of the baffle; there is maybe 1.5" clearance for the smoke to escape.

During the summer I had a floor AC unit (one that pushes hot air out through the window) on the main floor of the house and it was causing air to be pulled down the oil burner chimney and I was getting an "oil" smell in the basement if I didn't leave a window in the basement open. So I've been leaving a basement window open to mitigate the "smoke" smell from the wood stove chimney and it has remedied the problem as long as the window is open enough (needs roughly 2-3" opening).

The house was built in 1987, the 2 chimneys are on opposite sides of the house. The oil burner chimney runs from the basement to the second floor, the wood stove chimney runs from the basement level to above the first floor (wood stove is in a room with vaulted ceilings). I believe the insulation and windows have been replaced since new, and that the house is pretty tight based on the above experiences.

However, I don't know if the sole issue is negative pressure in the house. The plan is to install an OAK for the oil burner and the wood stove. Will that most likely solve my problems? As I stated above, the previous stove (old smoke dragon VC vigilant) never had any problems with smoke escaping with the doors open. I ran it as a fireplace with doors fully open from time to time. The only problem I have with that stove was that it would backpuff every once in awhile most often when it was windy outside or during an overnight burn. But I'm wondering if this behavior was also caused by negative pressure starving the stove of oxygen and causing back puffing.

Thanks for any input and sorry if I left out any important information.
 

ABMax24

Minister of Fire
Sep 18, 2019
1,522
Grande Prairie, Alberta, Canada
Does it still spill smoke if a window in the house is cracked open?

That will determine if you've got a draft issue or a negative pressure/air makeup issue within the house. Given your issues with the AC I'm leaning toward it being caused by a lack of makeup air entering the home.
 

neverstop

Member
Oct 11, 2020
135
new hampshire
Does it still spill smoke if a window in the house is cracked open?

That will determine if you've got a draft issue or a negative pressure/air makeup issue within the house. Given your issues with the AC I'm leaning toward it being caused by a lack of makeup air entering the home.

I don't believe I tried to open a window when I was attempting the fires. I have a newborn though so my memory is garbage currently and I may just have forgotten that I tried that. I was surprised by how much I had to open the basement window to mitigate pulling air into the house through the chimney, so even if I had cracked a window it probably wasn't sufficient. Cracking a window did almost entirely mitigate backpuffing on the old stove though.

Why does it smell worse when not in use now? Have the issues just been exacerbated by the SS liner?
 

bigealta

Minister of Fire
May 22, 2010
773
Utah, NJ
I'll take a stab here, sounds like make up air is needed. As to why the smoke smell in summer, i'll guess maybe your VC stove had the draft closed in the off season. With the new epa stove, the secondary air draft is not adjustable or closable? On my Jotul f400 the secondary air is not closeable and i'm not sure even the primary air closes completely in the closed position. So air from the flue could have an opening into your indoor space 24/7 with the new EPA stove.
 

neverstop

Member
Oct 11, 2020
135
new hampshire
I'll take a stab here, sounds like make up air is needed. As to why the smoke smell in summer, i'll guess maybe your VC stove had the draft closed in the off season. With the new epa stove, the secondary air draft is not adjustable or closable? On my Jotul f400 the secondary air is not closeable and i'm not sure even the primary air closes completely in the closed position. So air from the flue could have an opening into your indoor space 24/7 with the new EPA stove.

the secondary air intake is not adjustable on the current stove I have no idea where they're even located. Would installing an OAK and leaving the by-pass/primary air open result in a system that smells less since its open to outside air?
 

bigealta

Minister of Fire
May 22, 2010
773
Utah, NJ
So if you are needing make up air, it should help.
So why does air flow down a chimney?
1. House pulls it in to supply dryers, kitchen exhaust, bath exhaust, furnace, gas water heater, etc.
2. A cold surface (flue) cools the air inside enough to make it fall downward and thru any openings. Hot outside temps and cold air in the flue make this happen. Think Hot and Warm days with windows open all day. Cool air will drop down all day if not stopped.

Secondairy air inlet can be blocked by some tinfoil or the like if you can locate it on your stove.
 
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kennyp2339

Minister of Fire
Feb 16, 2014
6,545
07462
It sounds like negative pressure, but with no actual tests it hard to say for sure. The "oak" either way is a good idea as long as the intake isn't higher then the stove, if you have poor draft you dont want the "oak" to act as a secondary chimney, you may want to consider adding a damper to the black smoke pipe to keep closed off when the stove isnt in use, the other investment will be a co detector, if by any chance the stove is cooling off (ash and coal stage) and the draft reverses, you dont want co to leak back into the house.
You may also solve the stove draft issue with adding more chimney length, this would require adding a anchor plate to the top of the chimney for the liner and then a length of class a pipe.
During the summer I had a floor AC unit (one that pushes hot air out through the window) on the main floor of the house and it was causing air to be pulled down the oil burner chimney and I was getting an "oil" smell in the basement if I didn't leave a window in the basement open. So I've been leaving a basement window open to mitigate the "smoke" smell from the wood stove chimney and it has remedied the problem as long as the window is open enough (needs roughly 2-3" opening).
But this right here suggests that you have a tight house and that appliances that compete for air (mechanically) will take air from easy sources like the 2 chimneys, a fresh air intake or oak may solve that issue, but both the stove and boiler will need independent fresh air sources.
 

Rearscreen

Minister of Fire
Dec 21, 2014
768
Vermont
On page 23 of the manual: OPEN the bypass handle - towards you, Fully open the primary air - pull out towards you on bottom of stove, crack door slightly until kindling catches. I assume you did these 3 things? Adding an OAK to a wood stove is one thing, adding one to an oil burner is different as you are changing the air fuel mixture. The right test equipment is needed to adjust for it.
 

ABMax24

Minister of Fire
Sep 18, 2019
1,522
Grande Prairie, Alberta, Canada
I think your negative pressure issue still needs to be rectified regardless of whether an OAK is installed or not. Even with an OAK when the door is opened the house pressure will still be below that of the stove, pouring smoke into the house.

Just another note, is the bypass being opened before opening the stove door?
 

neverstop

Member
Oct 11, 2020
135
new hampshire
It sounds like negative pressure, but with no actual tests it hard to say for sure. The "oak" either way is a good idea as long as the intake isn't higher then the stove, if you have poor draft you dont want the "oak" to act as a secondary chimney, you may want to consider adding a damper to the black smoke pipe to keep closed off when the stove isnt in use, the other investment will be a co detector, if by any chance the stove is cooling off (ash and coal stage) and the draft reverses, you dont want co to leak back into the house.
You may also solve the stove draft issue with adding more chimney length, this would require adding a anchor plate to the top of the chimney for the liner and then a length of class a pipe.

But this right here suggests that you have a tight house and that appliances that compete for air (mechanically) will take air from easy sources like the 2 chimneys, a fresh air intake or oak may solve that issue, but both the stove and boiler will need independent fresh air sources.
Just got an OAK on the boiler today by heating company, need to source some materials for stove OAK

On page 23 of the manual: OPEN the bypass handle - towards you, Fully open the primary air - pull out towards you on bottom of stove, crack door slightly until kindling catches. I assume you did these 3 things? Adding an OAK to a wood stove is one thing, adding one to an oil burner is different as you are changing the air fuel mixture. The right test equipment is needed to adjust for it.
Yes, kindling caught fire. Primary was open and door was open extremely slowly. Heating company just installed the burner OAK.

I think your negative pressure issue still needs to be rectified regardless of whether an OAK is installed or not. Even with an OAK when the door is opened the house pressure will still be below that of the stove, pouring smoke into the house.

Just another note, is the bypass being opened before opening the stove door?
Wouldn't an OAK increase overall pressure in the house thereby reducing the problems associated with the negative pressure? Maybe not eliminating, but reducing significantly.

Yes, bypass is open when opening the stove door.
 

ABMax24

Minister of Fire
Sep 18, 2019
1,522
Grande Prairie, Alberta, Canada
Wouldn't an OAK increase overall pressure in the house thereby reducing the problems associated with the negative pressure? Maybe not eliminating, but reducing significantly.

Yes, bypass is open when opening the stove door.

Yes and no, if its a sealed connection it's really only delivering fresh air to the stove, in practice this isn't going to be perfectly air tight and some may leak out the stove or connections into the room. Whether or not it's enough to counteract the pressure imbalance is something can't say for sure.

I'm not knowledgeable on US codes. But in Canada we require a fresh air intake for the house that's alleviates many issues surrounding negative pressure in a home.
 

EbS-P

Minister of Fire
Jan 19, 2019
2,663
SE North Carolina
How long is the horizontal rear vent length before the T?
 

neverstop

Member
Oct 11, 2020
135
new hampshire
Yes and no, if its a sealed connection it's really only delivering fresh air to the stove, in practice this isn't going to be perfectly air tight and some may leak out the stove or connections into the room. Whether or not it's enough to counteract the pressure imbalance is something can't say for sure.

I'm not knowledgeable on US codes. But in Canada we require a fresh air intake for the house that's alleviates many issues surrounding negative pressure in a home.
I understand what you are saying. I also have no knowledge about the codes.

My assumption is that the oil burner was a large draw of air that no longer exists with the OAK installed. Even when not firing I'm assuming the draft was still pulling a decent volume of air up the burner chimney. So the situation should at the very least be improved
 

bigealta

Minister of Fire
May 22, 2010
773
Utah, NJ
Are you going to try a fire now and see if there is a difference.
 

bigealta

Minister of Fire
May 22, 2010
773
Utah, NJ
Yeah same here in NJ. Only 2 fires this season. Heat not turned on yet.
 

neverstop

Member
Oct 11, 2020
135
new hampshire
I started the fire with a top down method E/W loading, primary air full open, the door cracked, and a nearby window open 1.5". The fire took off pretty well. After the kindling caught and some of the smaller splits started to catch (maybe 5 minutes later or so?) I attempted to open the door. I slowly opened it and couldn't really tell if there was smoke escaping or not. The stove is still so new it is still off-gassing and smells; so it was hard to tell if it was smoke from the fire or smells from the new stove this time.

Once the larger splits started to catch I closed the door with the primary still 100 % open. I didn't keep track of time but maybe 15 minutes later it looked as if the fire was dying so I cracked the door and that somehow managed to snuff out the fire.

I'm wondering if I'm just not operating the stove correctly because I'm used to the old VC vigilant. I'm guessing the way I loaded the stove caused issues with this most recent attempt at a fire. So my questions are:
  1. Does air come in from the front of the firebox or the rear and top or bottom? Manual says to leave a trench and not obstruct the air inlet in the center front of the box, but the box has to be loaded E/W because it is shallow.
  2. Do EPA stoves need to be run "hotter/faster" at start-up compared to old non-epa stoves? Is there a sticky on best practices?
 
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begreen

Mooderator
Staff member
Nov 18, 2005
93,751
South Puget Sound, WA
Can you post a picture of the stove installation that includes the stove pipe. This stove will need a stronger draft than the Vigilant. The firebox on the new Shelburne looks almost the same as the GM60 which has exhibited the same symptoms. Seeing the install pictures will help spot issues.
 

neverstop

Member
Oct 11, 2020
135
new hampshire

begreen

Mooderator
Staff member
Nov 18, 2005
93,751
South Puget Sound, WA
Wouldn't an OAK increase overall pressure in the house thereby reducing the problems associated with the negative pressure? Maybe not eliminating, but reducing significantly.
If this is a basement install, then putting in an oak could be a problem. The oak needs to terminate below the firebox level. You don't want the draft to reverse and turn the OAK into a chimney.
Yes, saw that. I am going to close that thread. Having two threads on the same problem is causing confusion and redundancy.
Here is the setup:

20210916_112646.jpg 285780-2b3ad6b22ae1daea4161ec33f7cebba9.jpg
 

begreen

Mooderator
Staff member
Nov 18, 2005
93,751
South Puget Sound, WA
That is a short chimney. Insulating the liner would help, but the horiz. exit, then a 90º turn, then a shortish chimney appear to be providing insufficient draft for the stove.
Question: on the bottom of the liner tee, did they cap it or leave it open for the cleanout? It must be capped.
 
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neverstop

Member
Oct 11, 2020
135
new hampshire
That is a short chimney. Insulating the liner would help, but the horiz. exit, then a 90º turn, then a shortish chimney appear to be providing insufficient draft for the stove.
Question: on the bottom of the liner tee, did they cap it or leave it open for the cleanout? It must be capped.
Not a basement install. Its on the main floor but that section of the house is 1 story with a vaulted ceiling.

So the primary solution would be to extend the chimney vs just insulating the liner?

I'm not 100% on the capped tee, but my assumption is they didn't cap it in order to clean it out. The clean out for the masonry chimney is at ground level 10 ft below where the tee for the liner is located. How would the liner get cleaned if the tee was capped in this setup?
 

begreen

Mooderator
Staff member
Nov 18, 2005
93,751
South Puget Sound, WA
I'm not 100% on the capped tee, but my assumption is they didn't cap it in order to clean it out. The clean out for the masonry chimney is at ground level 10 ft below where the tee for the liner is located. How would the liner get cleaned if the tee was capped in this setup?
They would have needed to extend the liner after the tee down to the cleanout and then capped the liner at the cleanout so that it could be removed when cleaning. It probably is capped, but if it is not capped, that's a problem. It could ruin draft.
 

neverstop

Member
Oct 11, 2020
135
new hampshire
They would have needed to extend the liner after the tee down to the cleanout and then capped the liner at the cleanout so that it could be removed when cleaning. It probably is capped, but if it is not capped, that's a problem. It could ruin draft.
There is no liner down at the cleanout. I'll move the stove tonight and check the tee to see if it's capped. Not a great line of sight through the thimble though.