Winter-time downdraft (suggestions welcomed)

[ajthatch]

I have a Hearthstone wood burner in my basement. I enjoy using it in the fall, but when winter arrives I have issues with a bad downdraft through my chimney. I believe it is caused by my furnace creating a draw through the chimney. Once a downdraft has begun, it is hard to overcome it. It seems similar to a siphon action - once it starts it keeps going. I have even resorted to trying things like removing the chimney clean-out when not in use and stuffing an old towel in to prevent the downdraft from beginning (this gives only limited improvement and of course I have to remember to remove it when I want a fire). I imagine if I used the stove continually, there would be no problem since once I do get a draft going it works fine. However, I only use it a few nites here and there. Even after I get a draft going (usually by using a hairdryer) and I then let the fire die overnight, the next morning a strong downdraft will once again be going and the smell is not so pleasant. I'm at the point where I think I'll only use it in the fall (before it gets too cold to begin running the furnace). This is kind of a bummer since there are some cold nights when it would be really nice to have it going. Again, this seems to be a problem only when winter arrives and I'm using the furnace - I don't have downdrafts otherwise. Have others of you had similar problems? If so, I'd be interested as to any solutions you may have come up with. Thanks!

 

[Corie]

I'm not trying to ask a stupid question, but I just want to first be sure that the wood stove and the furnace are on two seperate flues?

My second question is, are the two flues in the same chimney? Do they terminate at the same height?

 

[wg_bent]

Corie, you didn't ask any stupid questions. If that stove is running (especially in the winter) you shouldn't have ANY down draft issues.

 

[Corie]

Yeah I suppose it isn't really that dumb! Thanks Warren! haha

THere are a few situations that I could consider causes of "downdrafts" and we really need more information about your installation before we climb into this one.

 

[webbie]

This sounds like smoke crossover - meaning when not in used one chimney reverses and sucks the smoke from the other chimney down into the living area. See (broken link removed) for some explanation.

So there are really two issues....

The smell and gases going from one to the other can be largely solved by raising one flue using that Boost-a-cap or a chimney pot or even the Proper Topper thing at http://www.extendaflue.com - preferably on the stove chimney.

As to the reversing flue, that is a common problem caused by many factors - but the basics are that cold air falls (and you probably have an exterior masonry chimney) - so the chimney is very cold and that cold air falls. Another factor is that the house wants to suck air in to make up for air lost - think of your home interior as a big chimney - air inside rises up and eventually finds it way out. The chimney provides an easy way for the house to get make-up air.

Lots of little things you can do - like cracking a window when you start stove, installing a tee or cleanout in chimney near wall so you can shove a piece of paper in and light to start chimney, line chimney, air to air heat exchangers (house pressurization), and even Exhausto electric draft fan on top of chimney.

Most important is to understand two separate problems - flue reversal and smoke crossover....the 2nd easier to solve.

 

[Corie]

You beat me to it Craig! I was going to recommend the extendaflue as well beause I was thinking that would be a good solution to the problem which I think is occurring here.

 

[Roospike]

Second thought ........... Why such a big downdraft ? Just a wood stove and a furnace in the basement ? gas hot water heater also ? Washer and DRYER? Big basement / half basement ? All units in one room ? Does the down draft increase when the furnace fan is running ? Lots of things to look at to narrow the issue down. Then there are things that can help once any issues there might be are fixed .

 

[ajthatch]

The furnace and wood stove each have their own separate chimney. The chimney for the wood stove is a through-the-wall type (metal pre-fab) and extends up the outside wall and through the edge of the roof. The height above the roof (at the point where it goes through the roof) is just over 4 feet (the total chimney length is 15 feet). The wood stove chimney is roughly 7 feet from the roof peak and extends above that peak by around 2 feet. The furnace chimney goes through the roof at the center of the house and is 20 feet from the wood stove chimney.

The only reason I bring up the gas furnace is that's the only thing I can think of which might be pulling air down the chimney (maybe creating a vacuum of some sort). On a cold winter's day, you can open the stove and feel the cold air just rushing in (if you light a match it can sometimes literally blow it out). In the past I've placed a hair dryer in the fire box and leave it for 5 minutes. At that point the draft will usually have reversed long enough to get a fire going. Once I have that going, everything is fine (but if I don't get it going fast enough, it's smoke city!)

I can take some pictures of the chimney and stove if that would help any. Thanks!

 

[ajthatch]

Didn't quite read all replies bofore I replied:

Second thought ........... Why such a big downdraft ? Just a wood stove and a furnace in the basement ? No - also washer/dryer (gas) and H/W heater (gas)

gas hot water heater also ? YES (in separate room with furnace and washer/dryer)

Washer and DRYER? YES (see above)

Big basement / half basement ? 1000 Sq Ft (150 sq ft utility room with furnace, gas water heater and wash/dry, 200 sq ft bedroom, 80 sq ft half-bath and the rest is open living space (where the wood stove is located) Utility room closed off with door.

All units in one room ? NO wood stove in living area - 20 ft from utility room

Does the down draft increase when the furnace fan is running ? (doesn't seem to matter - once the downdraft is going, it keep going even when furnace fan is off)

Lots of things to look at to narrow the issue down. Then there are things that can help once any issues there might be are fixed .

 

[Todd]

You have the same problem I had a couple years back. I extended one of my flues, and it helped to some degree. What really helped was this. (broken link removed to http://www.condar.com/asv.html)

Basements are notorious for negative pressure, especially with other appliances competing with each other. This ventilator will help equal out your pressures in the house. I placed mine down low about 3' from my stove. Problem solved.

 

[ajthatch]

Here is a pic of the chimney

 

[ajthatch]

For some reason I couldn't get this pic attached with last. This is the inside view. I have a window (basement type) near the stove. If I were to use an air supply ventilator as suggested, could I remove a pane of glass from the window and mount it there? (drilling another hole through concrete doesn't sound like fun - the chimney already goes through the concrete). Also, someone mentioned a chimney fan to induce draft - do you think it would work with this installation? Thanks again for the help.

 

[Todd]

Oh, it's an outside metal chimney. That could be the problem too. Are you going to build an insulated chase around it in the future? That would help. Those chimneys get real cold since their exposed to the cold air. It will take some time for it to heat up and maintain a draft.

 

[wtyamamoto]

If your house is very airtight as many superinsulated builds are today and your furnace draws combustion air directly from your basement rather than having an outside source, the loss of air pressure within your basement has to come from somewhere.

You said the draw down your stove chimney occurs when your furnace is firing, so I would tend to think this is occuring. Can you temporarily hook an outside air supply to your furnace and see if it cures the problem? If it you can and it does, you can go for a permanent fix. Another thing you can try is just open one of those basement windows I see in the picture and see if that relieves the vacuum and stops the downdraft.

 

[ourhouse]

I'm beginning to think I might have the same problem with my new install in my basement.

 

[Todd]

Window would probably work but look wierd. When I installed my ventilator, I drilled through the header just above the sill plate in a different room, and used dryer vent tube to run down low near the stove. But maybe you can install it near your furnace. Anywhere in your basement probably would help.

 

[wg_bent]

Interesting. My next door neighbor has an install that looks almost identical, and now and then she has some down draft issues. Her's happens now and then in the middle of the night. Stove is a small Avalon that's around 10 years old.

Does it happen while the stove is running?

I've never had any problem while the stove is running, but now and then if it's warm out... Like 40+ I'll get some smoke into the room while lighting a fire, but only if the stove is stone cold. My solution was to place my coleman camp stove in the mouth of the stove for 5 minutes to get some heat going up the chimney. Once I tried that trick, it never happened again.

 

[elkimmeg]

Lets assune a few things here 100,000 BUT furnace 50,000 BTU gas hot water heater and 20,000 btu used for the dryer wood stove 30,000 Btus According to code 50 cubic ft of air vollume is required for 1000 BTUs output for combustion appliances Plus the air removed by the dryer which is common to be 150 cfms. Assuming you have 7'6 ceiling height you have just enough combustion air for only the gas hot water heater and furnace. Everytime you run the dryer and the other appliances are on air has to come from some where. Enter your wood stove chimney once it gets cold and the down flow is being drawn in no wonder it is hard to reverse
Multiplying the problems as previously mentioned is the negavive pressures in the basement to begin with. So if you get that stove up and running it uses the air vollume that will short change all competing appliances none well be opperating properly in peak demand. You need to do a few things you need to bring in outside makeup combustion air and a that will also eleviate some of the negative pressure. One wat would to supply your largest appliance completely with an outside air feed./ A draft fan as suggested might work for you stove but would reak havoc increasing defeciencies to your other appliances. So for get that idea


Spike was on to this as were others, lack of combustion air from all competing appliances Is there also a bath fan in the Bath room?
another device removing the existing air air already lacking Unless your boiler room has louvered doors you are starving out all applainces from the required air of the entire basement That bedroom is removing that vollume of free flowing air. No appliance is working effeciently in that cellar. you need to address these issues if you have any hjope to getting the most effecient opperations for $$$ spent. I hope you have a carbon Monoxide sensor down there ans smoke detectors you mentioned one room being a bed room. Man this has to be addressed for you own personal safety. Many are here to help you. Your first step is outside air to the boiler room enought to take care of what is in there

 

[BrotherBart]

Help me out here Elk. The draft kit Todd suggested brings on-demand outside air into the basement, not the stove, to alleviate all negative pressure in the basement no matter the source. Why would that not help the situation?

 

[elkimmeg]

BB that outdoor air supply or pressure eleviation can be activated by a pressure switch turned on when pressure reaches xx and shut off when elevated to xx the only problem who wants to introduce 0 degree air without tempering it Now as I suggest one feeds the burner head or combustion chamber with outside air you are feeding it into a closed system not cooling down the entire area

 

[webbie]

Chimney looks good and should work good. I concur with everyone else that it is a negative pressure problem.

If anyone wants to really study the problem and solutions:
(broken link removed to http://www.gulland.ca/NegativePressureTestProtocolRPT.htm)

and

http://www.gulland.ca/reports.htm

 

[ajthatch]

Thanks, for all of the suggestions. I'm still a bit baffled by the force at which the air comes down the chimney - I would never have imagined that. As for the house being super-insulated, some extra insulation has been added over the years along with new windows/doors so I guess it is probably fairly tight. The furnace is around 10 years old and draws combustion air directly from a vent outside. Still, air is drawn back in through cold-air returns as well so I imagine there can be a pretty good pressure difference.

By the way, I have tried opening the basement window near the stove when I use it. Obviously I only do this when I'm getting ready to use the stove. The issue is that the down draft is still present even after I open the window and shut off the furnace fan. As I mentioned before, it's almost like a siphon- effect in that once it gets going it is hard to get it stopped. Getting out the hair dryer and warming up the fire box seems to be the only way to get it to reverse. I have considered enclosing the chimney and insulating it, but I have my doubts as to whether that will stop the problem.

One other question have is in regard to the indoor chimney pipe. This is double insulated pipe and it has slots in it (Security brand pipe). These slots are around the ends of each pipe section (you can see the inner pipe through these slots). In the winter when a down draft is going, I can feel cold air blowing out into the living space through these slots. I have often wondered if these are contributing to the problem. Would changing to a solid double insulated pipe be worth it?

 

[Roospike]

First I would like to say that a very nice looking install with your wood stove AND I love to see all that GOLD shimmering steel from the out side ( Ops , I meant STAINLESS STEEL = $$$ , ha. ) In my opinion only i think you have a lot of little different issues . The replies have stated them already .......... boxing in your chimney to help keep it warm and the cold and wind off of it even tho the stainless steel looks nice. All that stainless steel is going to draw a lot of cold onto it and make for a harder down draft. ( i hope the pipe is not on the north side of the house ) As we know , cold air is heavier than warm air and when the pipe gets cold its going to drop that cold air right down the pipe. The chimney needs to stay warm = box it in. I think elkimmeg stated your other options/issues with combustion air and some options for your basement . (post #10 ) The CO2 and smoke alarms are also a good suggestion. ALSO to help out with draft on starting a fire ( after you look into the other issues first ) you can always take a ceramic 1500 watt heater and put it on top of your stove aimed at the pipe (or in your stove ) to heat up your pipe and to get the draft going in the right direction before you build a new fresh fire . Be safe .

 

[ajthatch]

The help keeps coming - thanks!

To answer a few more questions - yes I do have both CO and Smoke detectors (and a fire extinguisher) in the basement. Currently, no one is using the basement bedroom. Also, the basement bathroom has no vent fan. Since I'm not up to speed on requirements for air supply from other appliances, I really appreciate the feedback given on this.

The basement stairway is opened to the upstairs (no door) so I don't know how that factors in either (obviously the kitchen vent, upstairs bath fan, etc. figure in to some extent. There are a few neighbors with burners in their basements (similar houses) but they don't seem to have the problem (at least not to the extent of mine). But I understand every install is different (although it is just a bit frustrating).

 

[elkimmeg]

Your situation with an outside metal chimney is a common situation. There are two type of class A chimnies the one you have using an air space between the liner and outer jacket and then more espensive the solid filled with insulation. In your case the soild insulated one reacts better at holding in the heat and drafts better. Roo and others mentioned another solution box in your chimney in an insulated chase or opt for soild pack clas A chimney. I agree that looks like a good install. We had a post last week where enhanced kindling startups might help slove your problems. You may use Fat sticks and build your fire adding bigger and bigger kindling to small splits to get it going. Pre heat options will also help. How dry is your wood?

Since you burner has an outside air feed then todd mentioned pressure relief as a pisibility but the open window should have done that