Chimney cap or not?

[Mark P]

Chimney used only for furnace vent. I usually recommend it be covered, but I guess it has been like this for 80+ years and I’m now wondering what is the point. Is there any benefit to covering the opening ? I never understood where the rain goes in this type set up, but I see it from time to time. And yes I see the bird nest.

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[kurt]

The miracle of old mortar & *breathable* masonry assemblies........

[Scottpat]

A cap would keep out water and would most likely cut the bird population to the point that you might be responsible for the endangerment of of an entire species. This in turn could upset the entire ecological balance of the local wetlands, thus impacting the sensitive balance of life on earth as we now know it. Think "Snail Darter", that little critter caused a whole lot of problems for some folks!

[]

[chicago]

I think that was a yes?

[randynavarro]

Yes, I always recommend caps even thought its old.

Water from soaked masonry can wick into the ceiling drywall inside, create musty odors in the basement (if there is one) and all sorts of undesirables.

No water in the building envelope. That's my theory and I'm sticking to it!!

[hausdok]

Well,

I'm just down the street from Randy and I don't recommend they put a cap on chimneys. Not because they won't help keep a little bit of water out, but because they just aren't necessary.

Probably 95% of the chimneys I look at around here don't have any caps on them and have never had any caps on them. Many of them are pushing 80 - 90 years old and the biggest problem they have is cracked crowns that allow water to permeate the stacks or they're in a serious hurt because they're unlined and someone had been venting either a furnace or water heater through them for decades.

The amount of water actually going into the opening of these is very little as far as I can tell. Don't know why - maybe it's because there's always so much heated rusing up through these that a whole lot of evaporation takes place. If people ask me if it's a good idea to add a cap, my response is usually, "It can't hurt," but I don't flog the things.

ONE TEAM - ONE FIGHT!!!

Mike

[kurt]

Well, think about it. That opening is approx. 1sf. How much rain actually falls in 1sf? Not much.

I think the benefit of the old mortar is missed by most folks. New masonry retains moisture & needs water mgt. systems to deal w/water. Old masonry deals w/moisture by the mass of the masonry; it soaks up a little, then evaporates it back out. Moisture mgt. is accomplished through mass, not flashing, wicks, & weeps.

It's part of my unified building theory; I'll get back to y'all when I get it completely figured out.

[Bill Kibbel]

It needs to be capped, but not because of the rain that might enter. The chimney is now a "cold" chimney since it is no longer venting what it was originally constructed for. There is now a moving cold air current and condensation will rapidly deteriorate the mortar in the joints at the coldest (top) part of the chimney (they're already eroding).

Soon, the bricks will begin to spall.

If it didn't have a cap in my area, they're would be a pair of glowing eyes in the second picture and the nest occupants would have been a snack.

[randynavarro]

What about the fireboxes on 40+ year old homes; specifically the rear of the box, where 9 of 10 times I'll see efflorescence and deteriorated mortar.

And don't forget rusted dampers.

Kurt, remember we're in Seattle. You're right. . . probably not a lot of water down 1 sq. ft. but a little water over an extended period of time adds up.

[kurt]

True. I know. I'd tell 'em to put a cap on it.

But.......

I look @ soooo many chimneys that are 80-100 years old lacking caps, tight joints around liners, and lacking any moisture resistant characteristics, and they are not in bad shape at all.

Why? I think its the composition of the masonry.

[hausdok]

Hi,

Randy, most of the efflorescence I see I can trace directly to cracked crowns. Where I've had intact crowns and good mortar, I don't think I've ever seen any serious efflorescence. About a month ago I was up on a roof in the pouring rain. When I looked down the stack, there was barely a trickle running down the inside of the stack.

However, the water at the back of fireboxes could simply be caused by warm interior air that's condensing on the back wall of a cold stack as it moves up into the stack and then it drains back onto the smoke shelf and into the brickwork. The dampers and stacks are cold, the warm air moving into the flue from the house is laden with moisture. It condenses on the stack and over a lot of years soaks through the stack. It's a theory, that's all.

ONE TEAM - ONE FIGHT!!!

Mike

[Erby]

Ya get 144 cubic inches of water down a 12" square chimney for every inch of rain. That's slightly over 1/2 gallon (0.62 gallons).

If the chimney is hot, some of that will evaporate.

I primarily recommend rain cap / spark arrestors for the wildlife and sparks, but who wants a 1/2 gallon of water down their chimney every time it rains an inch.

[kurt]

There has to be something that skews that # to much less water than a 1/2 gallon. Reason being, I've got an old chimney that doesn't have a cap cover; it's open to the remains of an old LR firebox. The opening is approx. 11"x11", not a SF, but reasonably close. ( I stuff it w/insulation in winter to prevent heat loss, leave it open in summer for "ventilation"; yeah, I know, I'm weird, but someday I'm putting a fireplace in there....)

In the 20 years there's never been a cap cover, I've never gotten any visible or apparent water down the flue. How's that work?

[Jim Katen]

Originally posted by kurt

There has to be something that skews that # to much less water than a 1/2 gallon. . .

I imagine that almost all of it hits the side of the chimney interior and simply gets absorbed into the brick or liner.

- Jim Katen, Oregon

[chicago]

Interesting thoughts.Would the water hurt the masonry more if it is from two sides?

Does it soak up more water and deteriorate faster?

[charlieb]

Originally posted by Jim Katen

Originally posted by kurt

There has to be something that skews that # to much less water than a 1/2 gallon. . .

I imagine that almost all of it hits the side of the chimney interior and simply gets absorbed into the brick or liner.

- Jim Katen, Oregon

Could the water be collecting on the smoke shelf?

What is a LR firebox?

[msteger]

I always recommend a level 2 clean & service by a qualified chimney professional.

This is whether there is a fireplace, wood/coal stove, or the chimney is used for exhausting the HVAC system.

[Jim Morrison]

You can't really say there's been no damage to the interior of the chimney until you've sunk a camera down there. Ask a chimney sweep with gray hair and they'll tell you that the presence or absence of a cap is one of the best indicators of the condition of the interior of the chimney.

[kurt]

Originally posted by Jim Morrison

You can't really say there's been no damage to the interior of the chimney until you've sunk a camera down there. Ask a chimney sweep with gray hair and they'll tell you that the presence or absence of a cap is one of the best indicators of the condition of the interior of the chimney.

That's right.

If one's being smart, they're recommending an NFPA Level II if it's a fireplace, or telling folks to put in a metal liner & cap if it's a natural gas combustion vent.

What if the sweep uses Grecian Formula? Is he still worth listening to?

[hausdok]

Hi,

I recommend level II's all the time.

I had a cute situation the other day. I wish I'd had my digital camera with me 'cuz you guys would have loved it.

Back in 1978, There was a mason who constructed this particular chimney with the flue just about an inch and a half off center. He didn't brick up or fill the void between the outer wythe of the stack and the flue tiles, so when he reached the top of the stack he had to cut a hole in a piece of plywood, rest it on the top course and then apply his mortar cap on top of that. The trouble is, he must have had one too many brews at lunch that day, because he installed his perfectly cut piece of plywood, applied mortar around the perimeter to hold it in place, and then slipped the flue tile into the hole before finishing up the crown.

Now I'm left to wonder whether he'd realized then that the hole wasn't aligned with the flue tiles, because that last section of tile is resting 1-1/2 inches off-center, and I was able to shine my light all the way to the bottom of the cavity between the flue tile and the stack. The opening was at the north side of the stack, so small wonder that the rain, which blows south to north here. had been going into that slot for years. and that the north side of the stack was wall-to-wall efflorescence at the bottom of the stack, while the firebox and the stack itself looked fine.

One has to wonder how lazy or stupid that fellow was to have left that like that all those years ago. Then it also begs the question: What the hell have all of the sweeps who've cleaned that flue over the past 28 years been saying about it?

[:-banghea[:-banghea[:-banghea[:-banghea[:-banghea[:-banghea

[Jim Morrison]

Shit Kurt, I still think you're worth listening to and I had more gray hair than you did last time I saw you.

I even listen to hausdok, and I don't think he's even a real doktor.

[hausdok]

Psst, hey Jimmy..... [:-censore

[Inspectorjoe]

This one from this morning didn't have a cap. Now that I think about it, it might have had a cap, but it could have fallen in. I wasn't about to get near enough to find out. [:-scared]

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[bmargiotti]

GREAT picture!! [:-bigeyes i would have fallen off the roof in enjoyment. thats a Chimney Swift nest with eggs and newborns in it.

[msteger]

I recommend chimney caps and a level 2 clean/service on all chimneys I see. There is too much down there that I can't see... missing or cracked or misaligned terra cotta, cracked bricks, missing mortar, nests and blockages, etc. Why take on all of this added liability?