Chimney condensation? Any experts out there?

[doublebase]

Hello,

I’m having a leak in my attic and it’s against the plywood where my chimney is on the other side. This ONLY is happening in winter. New roof (didn’t help), flashing (didn’t help).

Chimney inspection seemed to be at a loss for why this would happen. They looked down the heating side of the chimney (clay tile) and mortar was missing between the joints and some shifting. There are some cracks on the top of the chimney too, BUT it doesn’t leak in the summer even in hurricanes. Yet it leaks into the plywood every single day in winter.

I asked if perhaps condensation is getting through the mortar joints and behind the chimney, into the plywood. They didn’t seem convinced that was it. Yet they said I should get a metal sleeve down the chute anyway for safety and perhaps a stainless steel cap that will hang three inches out over the chimney. I was estimated $2,500 for the liner and $600 for the cap. Seemed like good guys.

Any thoughts? My thought is that the condensation is getting through and causing the plywood to get wet. But I’m not expert.

Here’s some pics of the attic.

 

[doublebase]

And here’s the chimney top.

 

[walterjay]

I would put in the metal liner and see what happens. The fact that you are missing mortar in the joints is not good.

 

[Snagglefoot]

Just wondering. There doesn’t seem to be a ridge board at the top of the rafters or is it just the angle of the photograph etc.

 

[vwmaniaman]

I think you are correct. I had a chimney that was 27 ft tall and it had cracks too. I finally installed metal pipe through the chimney. and mortored the top to it and installed a similar chimney cap. This stopped the leaks from the sides then the condensation would leak down into the cleanout. Sand in there would soak it up and just periodically shovel it out and replace it.

 

[vwmaniaman]

I agree Snagglefoot. I don't see that board either.

 

[MasterSolenoid]

My 2 cents -
I would also install a 'liner'.
By adding a 'liner' to the existing chimmney, you will be reducing the area where heat escapes.
The moisture should escape (more easily) along with any heat.

Just the opposite extreme:
If you had a 12 inch diameter liner, the heat would not travel up as much and any moisture would hang around in the chimmney.
If the heat/moisture started to rise in chimmney, the cool air in attic would cool it and the moisture would never leave the chimmney.

Like every thing today, I believe this can all be calculated by a good heating company.

Good luck.

 

[Vern_in_IL]

What is the purpose of the chimney? You got an actual fireplace or a wood stove piped into it?

Here in the midwest alot of older homes had the chimneys sealed up, and the ones that converted from burning wood just ran down double wall chimney pipe, but you need to get it lined.

 

[Fitter30]

On tv just the other day saw a chimney sweep company they cleaned the clay tile set up a gantry on top of chimney lowered a metal devise filled with grout pulled it up coating the clay tile. Then reworked the smoke self from the inside the house.

 

[doublebase]

Just wondering. There doesn’t seem to be a ridge board at the top of the rafters or is it just the angle of the photograph etc.

I actual,y had to look up what a ridge board was, but there is one there. It must be the angle of the photo.

 

[doublebase]

What is the purpose of the chimney? You got an actual fireplace or a wood stove piped into it?

Here in the midwest alot of older homes had the chimneys sealed up, and the ones that converted from burning wood just ran down double wall chimney pipe, but you need to get it lined.

The chimney is a fireplace - that I never use - and the exhaust for the furnace. There’s two sections in the fireplace.

 

[doublebase]

My 2 cents -
I would also install a 'liner'.
By adding a 'liner' to the existing chimmney, you will be reducing the area where heat escapes.
The moisture should escape (more easily) along with any heat.

Just the opposite extreme:
If you had a 12 inch diameter liner, the heat would not travel up as much and any moisture would hang around in the chimmney.
If the heat/moisture started to rise in chimmney, the cool air in attic would cool it and the moisture would never leave the chimmney.

Like every thing today, I believe this can all be calculated by a good heating company.

Good luck.

The interesting part is they said it’s an 8 inch pipe from the furnace. They will need to use a 6 inch liner to fit into the existing clay structure. And even then they said it might need to be widened.

It’s a big house and an older oil furnace. They said it was a big furnace and it’s putting out a lot of heat up that chimney too.

 

[Rand]

if its putting alot of heat into chimney that should be good it rises and takes the moisture out with it??

common problem is furnace is too efficient so you have to go power vent out side and not use chimney.

 

[hemitom]

older oil furnace roughly 30 to 40% of your heat is going out the chimmney so you are getting a lot of sweating on the cold clay pipes which then leaks through the missing mortar you need a liner..

 

[Gyro Gearloose]

+1 on hemitom's answer. I will just add that fuel oil is 13-14% hydrogen so the oil combustion is producing a LOT of steam. The engineering tables I looked at said the dew point temperature of oil furnace exhaust is around 100F to 120F - depending on excess air. If the chimney liner is colder than that at any point, or time, you will have condensation. You may be running a wet stack on the top part of the chimney with water trickling down the inside and migrating through the joints. A Liner sounds like a logical fix. Stainless steel to resist corrosion. Fuel oil still has a teensy bit of sulfur in it.

 

[doublebase]

I’m leaning towards the liner, if anything just for safety.

And I’m tired of worrying about this...the moisture, the wood, potential of serious damage.

I’ve already replaced the roof, and the chimney flashing. When they went up there today to inspect the chimney they said the flashing looked good.

 

[doublebase]

On tv just the other day saw a chimney sweep company they cleaned the clay tile set up a gantry on top of chimney lowered a metal devise filled with grout pulled it up coating the clay tile. Then reworked the smoke self from the inside the house.

I saw something like that when I was googling flue repair. Not sure what the prices are for something like this, or if they can even do that type of repair in the winter?

 

[oilcandave]

+1 on hemitom's answer. I will just add that fuel oil is 13-14% hydrogen so the oil combustion is producing a LOT of steam. The engineering tables I looked at said the dew point temperature of oil furnace exhaust is around 100F to 120F - depending on excess air. If the chimney liner is colder than that at any point, or time, you will have condensation. You may be running a wet stack on the top part of the chimney with water trickling down the inside and migrating through the joints. A Liner sounds like a logical fix. Stainless steel to resist corrosion. Fuel oil still has a teensy bit of sulfur in it.

This^^^...also if the chimney is right against the plywood a cold chimney and a warm day or moist air in attic space will cause this...of course a site specific problem...this happened at my house.

 

[Dinoburner]

Looks like the chimney is outside the structure which enhances condensation. so as said by others a liner is probably called for. An 8 inch vent is a large vent these days for the average home. Wonder what the AFUE rating and combustion efficiency is on this unit. Outside chimneys rarely maintain a good draw in cold climates which allows condensation.

 

[CDX825]

Oil furnaces don't create near the amount of water vapor as a gas or propane furnace. I could see some condensation in the chimney but not that much. The stack temperature of an oil furnace is also way higher than a gas or propane furnace so the chances of the flue condensing are way less.

I agree that a liner would be good but don't be surprised if it doesn't fix your issue.