Help!! Horrible back drafting furnace

[Hunter130]

Hi all!
New member here and unfortunately an unhappy one! I have a hotblast stove (1500) series I believe.. all the tags and decals are removed so I'm not 100% on the model.
Any how, it is in the basement and no matter how hot the fire, when adding wood it blows huge clouds of smoke back into the room. Secondly, if not a hot burning fire, occasionally it will seep smoke through the vent in front door, on some occasions even out the dampener on the very bottom ash tray door. I am desperate to get a fix for it, and in dire need. I have tried adding 4' of chimney to the pipe(already 3' of peak of roof), also clean the chimney every year(it's never very dirty). I have opened windows, pretty much any trick I can figure out and cannot get it to stop.

My fireplace in my living room, the next level above this furnace, does not have any draft issues what so ever. Any ideas of what I may be able to do?

 

[Lawson111]

Wet wood? Green wood? I to have been having this similar issue. I have found that when I (shut down) close the vents on the front blower and the knob on the ash pan my stove will get to air right and puff back. I have since open then vents more resulting in a hotter fire and my house being warmer but it’s seemed to stop the back drafting.... for now. I also removed my chimney cap because it was just collecting so much creosote but I’m afraid when it gets windy I the next day or two i might have to put cap back on. One more thing to check... is your ashes cleaned out so you can supply enough air under the fire to keep it going even with the knob on the door open?

 

[Lawson111]

https://www.hearth.com/talk/wiki/prevent-puffback-aka-flashback/

This also helped me understand why and what was going on when it happened. Good info here

 

[Hunter130]

Yes, burning very dry elm, and mixing locust and walnut with it. Seasoned and dry. Also, I should add that the vents are open fully pretty much always

 

[JRHAWK9]

are you absolutely sure your stove pipe and/or chimney are not plugged.....possibly by an animal nest?

 

[Hunter130]

I am not, going to find out tommorow, however, it has always been a problem while opening stove door to feed wood, even immediately after a fresh clean chimney. Also, it has gotten so bad that if I open the bottom ash tray door, it will actually cause smoke to push through the vent on the main door of the stove as well. Which is extremely strange to me because I should only be increasing draft by opening that door, correct?

 

[JRHAWK9]

yeah, it would increase draft if you have a draft to increase. Seems to me something is plugged somewhere.

 

[Hunter130]

Jrhawk9, that's definitely what it seems like. I guess I will know tommorow, however it has always been bad about smoking while opening the door to feed wood.. like burn you're eyes and stink you're clothes bad... I wonder about The way the pipe is ran? It comes out the back of the stove approx 1', then 90's up 3', then 90's again, followed by approx 3' horizontal before going out and up the chimney.

 

[taylorfarms]

does your fan run off of plenum temp or is it on all the time? we had a furnace in our shop when I was younger that was a smoky beast, that just had a fan that we switched on. when it got cold we were removing too much heat from the fire to overcome our poorly drafting chimney. It is a vicious cycle lower flue temp makes less draft, less draft makes less fire, less fire makes lower flue temp. this also plugs a marginal chimney even faster.

we finally put a temperature switch on the plenum that turned the fan off and on, then finally put a smaller fan on that seemed to eliminate the constant on and off cycling.

 

[Lawson111]

You said you added chimney length so I’m assuming it’s a double wall insulated chimney. Is one of the joints loose? Leaking? Seems odd to have one stove with no draft issue and another one in the house have issues. How close are the chimneys to each other?

 

[jatoxico]

New problem?

 

[Hunter130]

The blowers are ran by a on stove thermostat. They kick on when hot/off when cold. Yes it is a double wall insulated chimney, I do not believe any of the joints are loose or letting air/smoke escape on the outside. It appears to be pretty straight and also whenever a fire is going, even if it's smoking out my dampeners on the door, the chimney will be rolling smoke out the top like normal

 

[JRHAWK9]

Jrhawk9, that's definitely what it seems like. I guess I will know tommorow, however it has always been bad about smoking while opening the door to feed wood.. like burn you're eyes and stink you're clothes bad... I wonder about The way the pipe is ran? It comes out the back of the stove approx 1', then 90's up 3', then 90's again, followed by approx 3' horizontal before going out and up the chimney.

I would eliminate the 90's and put some 45's. This will make your 3' piece at a 45 and not horizontal.

 

[cumminstinkerer]

Hunter130, You summed it for me in the description of how you flue/piping is. you need to eliminate the 90's and go with say 45's and get that horizontal section out. Especially if the horizontal part is flat it will never draft well. Very bare minimum in three foot you need to come up like 6 inches. That horizontal section is acting like a blockage, remember that the smoke is rising due to the air temp difference, but in a horizontal run it really doesn't rise just becomes stagnant. If I remember correctly each 90 is the same as taking a foot of height off the chimney too. like I said take the 90's out go with 45's and get the pipe in between running up hill a lot more.

 

[Hunter130]

Hunter130, You summed it for me in the description of how you flue/piping is. you need to eliminate the 90's and go with say 45's and get that horizontal section out. Especially if the horizontal part is flat it will never draft well. Very bare minimum in three foot you need to come up like 6 inches. That horizontal section is acting like a blockage, remember that the smoke is rising due to the air temp difference, but in a horizontal run it really doesn't rise just becomes stagnant. If I remember correctly each 90 is the same as taking a foot of height off the chimney too. like I said take the 90's out go with 45's and get the pipe in between running up hill a lot more.

That is what my father in law suggested as well; however, how would I get the horizontal piece to not be horizontal as it goes through my block wall?

 

[JRHAWK9]

you need to limit the distance it's going horizontal. There's a big difference between 6" going into your chimney thimble and 3 feet.

 

[brenndatomu]

If I remember correctly each 90 is the same as taking a foot of height off the chimney too.

Make that 3' for each 90.

Put your 45 as close to the wall as possible...make the pipe through the wall the only horizontal section.

Also, how tall is the chimney? Is it a 6"?

Have you ever tried cracking a window or door to the basement...see if that helps? If so then you need a source of outside air to makeup what the furnace is venting up the chimney...in other words, the house is too air tight. But even drafty houses can still pull a "vacuum" on the basement...make a chimney smoke back.

Any new changes to the house? Air sealing, insulating?

A vent fan running more now than before, or clothes dryer? These all compete for makeup air...

 

[maple1]

As always with threads looking for help - pictures can be quite helpful.

 

[cumminstinkerer]

Make that 3' for each 90.

Put your 45 as close to the wall as possible...make the pipe through the wall the only horizontal section.

Also, how tall is the chimney? Is it a 6"?

Have you ever tried cracking a window or door to the basement...see if that helps? If so then you need a source of outside air to makeup what the furnace is venting up the chimney...in other words, the house is too air tight. But even drafty houses can still pull a "vacuum" on the basement...make a chimney smoke back.

Any new changes to the house? Air sealing, insulating?

A vent fan running more now than before, or clothes dryer? These all compete for makeup air...

Thank you, I couldn't remember for sure but I new it had a huge effect

 

[cumminstinkerer]

Hunter130, that does become an issue, about the only thing you can do there is enlarge the hole and at least get it angled up as much as possible then Hydraulic cement back around the pipe to fill the bigger hole in,

 

[Marshy]

Jrhawk9, that's definitely what it seems like. I guess I will know tommorow, however it has always been bad about smoking while opening the door to feed wood.. like burn you're eyes and stink you're clothes bad... I wonder about The way the pipe is ran? It comes out the back of the stove approx 1', then 90's up 3', then 90's again, followed by approx 3' horizontal before going out and up the chimney.

This could very well be your issue. Are the horizontal pitched with at least 1/4" per foot of horizontal run?
Can you use two adjustable elbows, one at the back of the stove, the other at the chimney connection and run a continuous straight section between the two elbows? If yes then that is what i would do.
DuraVent makes double wall 6" and 8" diameter adjustable elbows. I don't believe Silkirk makes as adjustable elbow. However most offer 45 and 30 degree fixed elbows.
Do you know the maker of your flue connector between chimney and stove?

 

[Hunter130]

I don't know the maker... I will try to get a picture of it here shortly. Also, I should add that currently my ckeanout outside is open. I just talked to someone at a stove shop that suggested I cap that clean out off and see what happens. Fingers crossed that will work

 

[Marshy]

I don't know the maker... I will try to get a picture of it here shortly. Also, I should add that currently my ckeanout outside is open. I just talked to someone at a stove shop that suggested I cap that clean out off and see what happens. Fingers crossed that will work

That is a huge issue to have it open. It draws cold air into the chimney and mixes with the hot flue gas. When the flue gas gets cold from the mixing it will kill your draft. Draft is generated from buoyancy effect the hot air has vs the outside ambient air. Not only do you need to close the clean out door but you need to seal it. I suggest you get some plumbers putty and make a bead all around the door and close it so the door squishes into the putty and makes an air tight seal.

How much distance is between your clean out door and where the thimble is that connects the stove to the chimney?

Some people have advised me in the past to take some unfaced fiberglass insulation and reach into the thimble and shove it below where the thimble enters the chimney. It theory it helps to separate the stagnant cold air below the thimble but above the clean out from cooling the flue gas. The only problem is that fiberglass insulation is combustible so it's not thst good of an idea.

 

[Hunter130]

To be honest, I'm not sure what the thimble is.

 

[brenndatomu]

Also, I should add that currently my ckeanout outside is open. I just talked to someone at a stove shop that suggested I cap that clean out off and see what happens.

Ahhh, yeah! That is 99.99% of the issue then!
Surprised it works at all!