would negative pressure impede my stoves heating ability

[phil ward]

I installed an avalon spokane last year and it doesn't throw nearly as much heat as my old non air tight acorn brand stove. I was told by a factory representative that the problem sounds like negative pressure but my stove contractor doesn't agree. He suggests that we install a device that will warm the chimney prior to lighting. I plan to put a thermometer on the stack and hope that will provide more information so that i can solve the problem.
My stove is in the basement and I have a masonry chimney that is on the exterior of the building.Any input would be appreciated.Phil Ward

 

[Backwoods Savage]

Welcome to the forum Phil.

It is common to have poor drafting when the stove is in the basement. The thermometer on the flue will tell you the temperature there but that won't be of help knowing about draft.

Have you tried stuffing some newspaper in the flue and lighting it before starting the fire in the firebox? Maybe even a torch or a hair drier? How about opening a window until the fire gets established?

btw, the masonry chimney doesn't help a lot. What size is it or do you have a liner?

 

[jimbom]

This might help:

http://www.woodheat.org/how-chimneys-work.html

Perhaps the new stove has more pressure drop than the old. So now, you need a little more power in the chimney.

 

[begreen]

Welcome Phil. An EPA stove often will require more draft to pull air through the secondary passages and manifold. If this is the case with your stove, then improving draft will improve the burn.

However, at this point we need a bit more information. Could you escribe how you are running the stove once the fire is going? There are other variables that might affect draft.

1) Do you get smoke spillage when first start a fire and open the stove door? If yes, that indicates weak draft.
2) How dry is the wood you are burning? When was it cut/split and stacked? What species? An EPA stove really likes dry wood. You might try some carpentry scraps in a test fire to see if this makes a big difference.
3) Have you tried opening a near to the stove window or door a little to see if that improves draft? If so, the stove may need an outside air kit (OAK).
4) Do you have windows or doors open upstairs or an exhaust fan running? Try closing them or turning off the fans to see if this improves the heat output.
5) Can you describe the flue and chimney setup? How is the stove connected to the chimney and how tall is the chimney? If the stove has elbows or a short chimney, draft can be weak. Connecting the stove with 45's, lining the chimney, or adding an extension to the chimney are some solutions if this is the issue.

 

[phil ward]

Welcome Phil. An EPA stove often will require more draft to pull air through the secondary passages and manifold. If this is the case with your stove, then improving draft will improve the burn.

However, at this point we need a bit more information. Could you escribe how you are running the stove once the fire is going? There are other variables that might affect draft.

1) Do you get smoke spillage when first start a fire and open the stove door? If yes, that indicates weak draft.
2) How dry is the wood you are burning? When was it cut/split and stacked? What species? An EPA stove really likes dry wood. You might try some carpentry scraps in a test fire to see if this makes a big difference.
3) Have you tried opening a near to the stove window or door a little to see if that improves draft? If so, the stove may need an outside air kit (OAK).
4) Do you have windows or doors open upstairs or an exhaust fan running? Try closing them or turning off the fans to see if this improves the heat output.
5) Can you describe the flue and chimney setup? How is the stove connected to the chimney and how tall is the chimney? If the stove has elbows or a short chimney, draft can be weak. Connecting the stove with 45's, lining the chimney, or adding an extension to the chimney are some solutions if this is the issue.

Thank you for the excellent questions and suggestions ! I definitely get significant smoke spillage when I try to light the stove. I find it impossible to get the stove lit without pointing an industrial fan toward it .
This season I have three cord of hardwood that has been seasoned in a shed for three years so I think that my wood is good . I will definitely try the "carpenter scraps idea".
I have not tried opening a window an idea that I will definitely try.
I am running a straight six inch pipe into a masonry chimney.The stove is below grade which I believe is a part of the issue.
The stove salesman wants me to put a thermometer on the stack and use that information to determine the next steps. He also suggests that we install an electric chimney heater. The chimney heater is supposed to make starting the stove easier but it will not address the lack of heat from the stove. Even when the stove is running open with a decent fire my basement that is well sealed is a best luke warm. I appreciate your input because I thought that buying an airtight stove would improve our heating but it has not actually my little acorn stove did a better job as in it actually warmed the house using the same chimney system.

 

[Backwoods Savage]

Phil, is this basement insulated?

 

[fossil]

The Avalon is not an "airtight" stove. No modern stove is. Sounds to me like you need to do (at a minimum) two things: 1.) Install an insulated full height liner inside that exterior masonry chimney, from the stove to daylight. 2.) Get busy insulating that basement. Rick

 

[DanCorcoran]

"...my little acorn stove did a better job as in it actually warmed the house using the same chimney system. " Granted, an insulated basement is a big plus, but his Avalon should produce more heat than the Acorn, if it's running right.

 

[begreen]

Phil, try opening a nearby window with the next fire. It doesn't have to be a lot, just an inch should do. The Avalon will heat much better once it has proper draft.

Do you know the interior size of the clay liner in the exterior chimney? If not, can you measure it? Also, if there is a cleanout door on this chimney, make sure it is sealed shut. You can use duct tape to do this temporarily.

 

[phil ward]

My basement is well insulated. One thing I realize is that neither the chimney builder nor the stove dealer gave me the straight dope on my situation. It seems that they would have known the problems inherent in my set up. I am wondering whether I should cancel the chimney warmer and get an insulated liner installed. Do you think that it would be worth it to spend the money for both which would be an easy thousand dollars?
I will check the ash door for a tight seal first thing in the morning. I think that the stove is not pulling enough air through itself.
Everyones comments are certainly appreciated!Phil

 

[Backwoods Savage]

Phil, I do think the liner would do much more than an electric heater in the chimney. You can always heat that chimney with a propane torch or wadded up newspapers, etc. The liner in the masonry chimney should help immensely. Remember that there does need a certain amount of heat in the chimney in order to exhaust the smoke and gasses and once you get the heated chimney it should be no problem. Also, as the air turns colder outside, there will be a greater temperature difference and that alone will help with the draft.

 

[fossil]

If your 6" diam. stovepipe is just stuffed a little ways up into an exterior masonry chimney structure, that could well be a whole bunch of the draft problem right there. The cross-sectional area of your stovepipe is ~28 in². NFPA 211 guideline says in this sort of installation, the cross-sectional area of the masonry chimney flue should be no more than twice that of the stovepipe (ideally, it should be the same all the way to daylight). So, if your masonry chimney flue is ~7½" x 7½" or larger, then what you've got is an unacceptably large increase in area as the flue gases try to move from the stovepipe up into the flue. This will cause the gas flow to slow way down, resulting in both poor draft and lazy upward flow, allowing the flue gases to cool more than you want before they go to daylight, which increases the probability of creosote condensing out onto the inside surfaces of the flue. Overall, not good configuration. Rick

 

[DanCorcoran]

Yes, it's counter-intuitive, but a smaller diameter flue/chimney will produce a better draft than a larger one, within reason.

 

[phil ward]

I had my stove contractor install a chimney heating collar at a cost of close to 500.00 dollars despite the expense the collar has really helped the start up. I would recommend the heating collar to any one who has a similar issues as i described earlier. My current concern is that my stack temperature is only running between 350-375 and i think it should be more in the 400- 450 range is this correct?

 

[shawneyboy]

The one problem I see with the heating collar is that although it addresses the start-up problem it does not address what sounds like a poor draft problem due to an oversized flue. Do you know the demensions of the flue itself ? If you were to put an insulated chimney liner down and connect it properly, I bet you would have addressed both the start up and the poor draft problem. You know 2 birds with one stone.

I am willing to bet, depending on the size of the flue itself, you may be cooling those gasses way to much, prior to "reaching daylight" as was suggested earlier in this thread. Modern EPA stoves need the correct size flue to run properly and safely. The flue is the engine of the system.

If the flue is the wrong size it is like putting crappy gas in a high performance vehicle, yeah, sure, it will run, but ........

Shawn

 

[begreen]

+1 If the chimney is too short or restricted or oversized, the flue heater may solve some symptoms, but may not not the core problem.

We still dont know: The liner diameter, the chimney height, and how the stove is connected to the chimney. Can you provide this information?

Also, if there is a clean out door on this chimney and it is not sealed shut, it could cause draft issues. A temporary test for this would be using some duct tape to seal it.

 

[phil ward]

i appreciate everyones input I am not sure of the liner diameter and the chimney is well above the roof line. I will definitely check out the clean out door today and seal if necessary. My plan is to run it this way this winter and have an insulted line installed next year before winter. On another note I am having a high efficiency gas furnace installed this week. My installer has told me that the furnace will help with air circulation.

 

[begreen]

Hopefully the furnace have its own outside air supply. If not, the furnace will be a competitor for air with the stove. Usually when folks have the wood stove going the furnace remains off, so the affect of the new furnace could be nil.

You can measure the current liner by pulling the thimble connection, then with a flashlight peer inside and take a rough measurement. You might also be able to do this via the clean out door.

So that you don't have to repeat procedures, can you update us on what you have tried so far?

1) Have you measured the temperature on top of the stove (not the flue pipe)? If yes, what is it reading on the stove top?
2) Have you opened a nearby window or door a little (1" is plenty) to see if the fire improves?
3) Have you confirmed that your wood is fully seasoned? When it is resplit, the fresh surface of the wood is dry and warm if placed against your cheek?

 

[Jackfre]

Your flue pre-heater is treating the symptom without treating the problem. The problem, as noted is an outside, oversized masonry chimney and maybe a combustion air issue. If the neg pressure is a factor you have the killer double whammy here. In my years as a factory built chimney rep I cannot tel you how many times a customer with a problem would call and say, "I wanted to make sure i had plenty of draft so I bought the 8" chimney instead of the 6" that is the size of the flue collar." to large a flue is not only costly, but CREATES draft problems. Oversizing on factory built can be problematic. Oversizing on a masonry flue, especially on that is exterior, is a double whammy. When a gas expands, it cools. The tightly pack heat molecules in the proper sized flue connector blow into a much larger space larger space where the hot molecules are then surrounded by many more cold molecules. Your flue velocity stalls, the stack effect collapses, the unit smokes and generally cannot operate up to capacity.

Your fix is not the flue starter, imho, but a properly sized factory built chimney (my preference) or again as noted, an insulated liner in your chimney. If I was worried about negative pressures I would check, after the open window test, to see if I could get an outside air kit for the stove. Good luck!