Chimney draft

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jarvis

New Member
Oct 2, 2009
26
midwest
I have a Woodchuck 2900 indoor furnace that I started using regularly this winter. It heats the house well, but I'm wondering if my chimney is pulling too much of a draft. I have two sections of black pipe with two elbows connecting the furnace to the chimney, and about 30' of 8" insulated pipe outside. I also have a thermometer mounted on the black pipe right next to the elbow thats connected to the flue. With a good, hot fire it usually runs in the 300-350 degree range.

Here's my concern: I've noticed many times when I have a fire going, there is so much draft suction it will actually spin the wheel on the draft blower, even though there is no power to it. Also, when I have a good fire the furnace blower runs constantly...sometimes for two hours straight. I keep my thermostat set at 68 but its got as warm as 75 in here. It seems that even without the draft blower running that its still sucking too much air, causing the fire to burn hotter than it needs to. But, my flue temperature appears to be in the normal range so its not like my fire is burning too hot. I have a manual damper on the black pipe but I haven't tried shutting it down yet.

Any thoughts?
 
It sounds like you have an overdraft with a chimney that tall. Ours is a 5.5" insulated liner thats 32' and its too much. With a woodfurnace as long as there is fuel in the firebox the blower will run. Thats the nature of a woodfurnace. If you want less heat, then smaller fires farther apart will help. As far as your flue temps they aren't bad. Without having a true secondary combustion furnace, you want that heat which helps keep the flue clean. It sounds as if your forced draft fan is letting alot of air into the unit. If your not needing it, then close the fan if you can. You can close the flue damper maybe 1/4 way for a start and see how that works. How often do you have to load the furnace?
 
laynes69 said:
It sounds like you have an overdraft with a chimney that tall. Ours is a 5.5" insulated liner thats 32' and its too much. With a woodfurnace as long as there is fuel in the firebox the blower will run. Thats the nature of a woodfurnace. If you want less heat, then smaller fires farther apart will help. As far as your flue temps they aren't bad. Without having a true secondary combustion furnace, you want that heat which helps keep the flue clean. It sounds as if your forced draft fan is letting alot of air into the unit. If your not needing it, then close the fan if you can. You can close the flue damper maybe 1/4 way for a start and see how that works. How often do you have to load the furnace?
There's really no way to close off the inlet to the draft blower. Usually I get home from work around 6 PM and start a fire. It takes about two hours to get a good bed of coals before it starts putting out steady heat, so I fill it about 3/4 full around 8 PM. By 10:30 its mostly burned out, so I fill it completely full before going to bed at that time. I've never checked what time its burned out, but I would guess around 3 or 4 AM. There are still enough hot coals left to restart it the next morning.
I have no complaints with the heat output; it does an excellent job heating the house. But, it seems like there is a bit too much draft since there is enough suction to cause the draft blower wheel to spin.
I briefly read the thread about measuring draft. Not something I have the equipment to do right now...but maybe in the future. Hopefully in another month I won't be using it as much.
 
I thought about the forced draft, and in that case using the manual damper probably isn't the best option. For around 40.00 you can get a manometer which then takes just a few seconds to verify draft. Thats quite a bit of wood to burn through. No doubt its heating well pushing that much wood. If the manufacturer suggests it, a barometric damper will help keep draft under control. The downside to one is a decrease in flue temperatures and possible accumulations of creosote. But keeping an eye on things and cleaning when needed will help keep things safe. You really need to get that draft under control and your wood usage should drop a bit. That furnace has a huge firebox, actually double the size of ours and we go 8+ hours on a load of hardwood.
 
Hi All. If you are still out there I have a question for you. I Just setup an older woodchuck in my basement and am having a little trouble getting it to burn hot. Did you guys run an outside air inlet to your combustion fan? Also, when you say you fill up the furnace, just how full do you make it? Up to the top of the fire brick?
Thank You!
 
I just about guarantee that you have high draft with the results you are getting. If you don't want to install a barometric draft regulator, just spend $10 on a key damper for the pipe. You just can't close it down too far or the draft blower will be blowin smoke in the house! Also, as laynes said, get a manometer. $20 will get you a Dwyer Mark II on fleabay if you shop and wait a bit. The Mark II works great for chimney draft, I leave mine on all the time.
 
Thanks for the advice. I actually put a damper in the other day and it did help a little. I was wondering if the combustion blower is forcing too much air under the fire as opposed to above it. The new furnaces have what Meyer calls and 80/20 switch. Mine does not have this and I was going to try to partially block off the lower output an see if that helps. How do you leave the manometer in all the time? Doesnt the plastic hose melt?
 
Doesnt the plastic hose melt?
Attach the hose to a copper tube that is stuck into the pipe...foot or two long, it's completely cool by that point
 
Make sure you have a good flue temp guage too, so you can also assess how much heat is going up the pipe.

I used a section of brake line for my Dwyer tube. It came with fittings that I used to hold the line in the flue pipe hole. Just picked something out of the bin at the parts supply place that looked right & was right diameter & went with it.

But not sure what you mean by trouble getting it to burn hot. That could mean you don't have enough draft for the fire to burn right, and damping it would make it worse in that case. What is the size & type of your chimney? Could also be a sign of wood not dry enough.
 
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