Bad draft - is it humidity and rain?

[jwscarab]

Hi all, I have been burning for years now and all of a sudden I have smoke coming out the door of the stove when I open it. I am burning 24/7 so its not a start up issue. I keep my flu very clean - its a 6" ss run up almost 30ft thru my clay liner - outside wall masonary chimney. Birds could have not built a nest as I've been burning 24/7 for months.

So my question is - could this be weather related? It is VERY humid right now - maybe upper 40's - been raining for 2 days - everything is sopping.

I have about 2 days of wood left in my basement to burn up before I run out. Then I am going to quit for the season so I dont want to stop now. And the roof is too wet to climb up and take a peek down the flu anyway.

I've felt fortunate to always have strong drafts. Is the air so wet and humid and heavy my draft is too weak? I have never had this happen before - in all weather conditions.

 

[Jimbob]

I do suspect the relitively warm weather and high humidity is causing that.
If the fire is already going, you should have enough draft to overcome that.
Was that from a cold start, or a hot re-load?

 

[begreen]

Low pressure possibly? When it combines with mild temps, draft can be poorer.

 

[jwscarab]

This is from a hot reload. Its burning fine but if I open the door - smoke comes out the door half way decent flow into the room - during mid burn! So I have to relaod quickly and shut door!! Thanks again!

 

[bogydave]

I get that too sometimes. Low pressure area & high humidity.
I have to burn a little hotter (more inlet air)
To compensate for not getting the house too hot, I burn smaller fires hotter to keep
the flu hotter so it drafts well.
I think you hit the problem, weather changes effect stove more than some think.
Air to fuel mixture adjustment, you should be able to finish your burn season.

 

[jimbom]

I get that too sometimes. Low pressure area & high humidity.
I have to burn a little hotter (more inlet air)
To compensate for not getting the house too hot, I burn smaller fires hotter to keep
the flu hotter so it drafts well.
I think you hit the problem, weather changes effect stove more than some think.
Air to fuel mixture adjustment, you should be able to finish your burn season.

BogyDave makes sense to me: Give it a little more air and a little less fuel.

This web pagehttp://webdh.munters.com/webdh/BrochureUploads/Munters High Temp Psych Chart.pdf is a psychrometric chart.

However, there is very little difference in the weight of air at the same temperature and different relative humidity. If you look on the psychrometric chart, 50 F air at relative humidity of 20% is in the very lower left corner. The intersection of 50 F and 20% RH is just to the left of the 13 ft^3/lbm of dry air line. You could say 50F-20%RH air is about 12.9 ft^3/lbm of dry air. Following the 50 F line up to 90% RH you see the intersection at 13.0 ft^3/lbm of dry air. So the difference between 20% and 90% RH at 50 F is a very small 0.1 ft^3/lbm of dry air.

Compare to a flue gas temperature of say 250 F and 4% relative humidity. This is on the top right of the chart and shows an intersection at about 19.4 ft^3/lbm of dry air. So a pound of 250 F air takes up 19.4 cubic feet and a pound of 50 F degree air takes up either 13 cubic feet at 90% relative humidity or 12.9 cubic feet at 20% relative humidity. Not much change in the draft from feed air humidity. Especially when you think about the same outside air is on the intake side of the stove and on the exit side of the stove. All in all, relative humidity should be a wash when it comes to draft. Especially when it is compared to the big effect from temperature difference across the stove. I am sure somebody on here has a better handle on this regarding wood stove operation than me and will be able to straighten me out.

Air at the same temperature, but a higher relative humidity is lighter than dryer air at that temperature. That always seemed wrong to me. But if you think about it, clouds are usually in the sky. And the condensation on the mirror when you take a shower starts forming at the top of the mirror, not the bottom.

Rereading this makes me think I need to get a life.

 

[begreen]

This is from a hot reload. Its burning fine but if I open the door - smoke comes out the door half way decent flow into the room - during mid burn! So I have to relaod quickly and shut door!! Thanks again!

Got that yesterday morning under similar circumstances. 43ºF outside, stove warming up with a new fire. I had a piece of holly on top of the fir bed that wasn't in an ideal place to ignite. Foolish me, I opened up the door and moved it with the poker. It rolled over to the side of the fir and snuffed itself out. Smoked like the dickens, so I closed the door and just said screw it. Later on I went up and checked the flue pipe and cap. All fine up there, but still I got a snootful of smoke. Will try again tomorrow morning as we have a high building now. But not today, it's 50 outside. Time for the first mowing.

 

[NH_Wood]

This time of year makes having small splits very important. I just finished (yesterday) resplitting a lot of my bigger splits into ~ 2" splits. When it's in the mid to upper 40's, I don't need a lot of heat, and a medium size load of smaller splits takes off much better, and gets the stove hot enough. Even with decent coals, warmer temps and slower draft can make a bear of getting larger splits to flame quickly - I don't like the longer smoke period. Cheers!

 

[Battenkiller]

Air at the same temperature, but a higher relative humidity is lighter than dryer air at that temperature. That always seemed wrong to me.

Yeah, it's kinda counter-intuitive. We think of water as being denser than air, and it is when it's in the liquid state. Water vapor, however, is a gas. Fact is, water molecules (H2O) weigh less than nitrogen molecules (N2) or oxygen molecules (O2). Therefore, the more water molecules in the air, the lighter the air will be... even though it often "feels" heavy to us, especially on hot, muggy days.

BTW I never have any of these weather-related draft problems. I must be doing something wrong. Either that, or it's the 25' tall chimney. ;-P