chimney cap question

[maccrazy2]

Hello all. The hide has never let me down before so here is another question for you guys.
I have a 2 level house with a fireplace on each floor. Both flues are side by side exiting the roof and are in the middle of the brick fireplace. They are approx 10 in square masonry type material. They have been covered with a board since I bought the place. I did remove the board and burned both fireplaces in the past but had a bad snowstorm and could hear water dripping in the basement 1 time so I replaced the board to keep the weather out. I never used the fireplace anymore anyway.
Fast forward 10 years and now the old lady is living here and is excited about using the fireplace this winter. Lol I was out sweating balls at the range today and she is thinking about fires? Anyway, I let her know I needed to look into a cap too keep the weather out of the vents but let the smoke out. I will get exact measurements this week when I get up on the roof. It is approx 40in long by 18 wide . I was looking at some caps that slide over the whole chimney that have expanded metal sides and a peaked roof. I threw in the above measurements in one place online and it says $1100 plus shipping.
I have all the equipment to fab my own. Does anyone know anything about doing something like this? I guess I just need to know how tall to make the sides so smoke can exit properly as well as notbe too tall so snow doesn't get in when not in use. I seem to remember something about airflow/ siphon effect in chimneys but I have no idea if that is an issue or not. Any help is appreciated.

 

[pawprint2]

What you need is a chimney spark arrestor, they come in almost every shape and size, you'll find one that looks good on your house. Google, Chimney Spark Arrestor and you'll be set! Good luck!

 

[MarshalTex]

My dad is a homebuilder been at it with him since I coukd walk. If you can fab your own go for it itll save you big money. Spark arrestors are for living in the forest ect. We never put one on a house. Typically however we had our hvac guys buikd the chimney vap for us out of galvanized and then had the painter shoot it while he was painting the drip edge and flashing for the house. Theres no rule of thumb to follow just make it to what you think looks/functions best with ample export for smoke and a lip to go over edge of chimney to kick water onto exteroir of the fp.

There are logistics on height of fireplaces for drafting reasons and it really only applies to the chimney being to low as wind would come over the ridge of you house and cause a back draft filling house with smoke. As long as the fp functions now you shoukd be good. I would. However add screen to keep the swallows out. And by swallows I mean birds the other kinds are ok

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[maccrazy2]

Thanks I will get up there this week and take some measurements for materials. I think I will make a template out of cardboard and see what looks right for height of the sides. There is a lot of surface area so I don't expect there to be a big issue with interrupting the smoke flowing out..
One other thought is anchoring the cover so the wind can't rip it off. Do you think masonry screws around the perimeter would work? I never put them in brick before.
I did use some lead anchors that take a screw . I will ask at the hardware store

 

[rookie101]

tapcon blue screws are a very effective masonry fastener and will work fine in brick or cmu. If drilling into cmu turn the hammer off on your roto hammer or masonry drill as you may blow out a lot of the inside of the block. If you have two flues coming through one chimney, you should have a galvanized cap with down turns that is cut out for both flues, cross bending to give a little slope away from the flues is a good idea. Then a preformed cap for the flues can be bought anywhere. If you have two ceramic flue liners you are on the right track, however in my neck of the woods you rarely see or worry about it. As long as you don't affect your draw you can do what you want.

 

[MarshalTex]

+1 for tapcon

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[DocB]

mac,

Check with your insurance company, they usually require a UL certified cap or spark arrester to keep the insurance in force.

HTH,
DocB

 

[maccrazy2]

thanks guys, I found some more genaric style caps online today. They are much cheaper than the ones I was looking at before.
I will look into the insurance requirements just to make sure I dont screw myself

 

[xs hedspace]

You can probably get two caps, one for each flue, and it would be an off the shelf item, just slides into the ceramic flue pipes. If the space between is enough for the cap roofs. This would lessen the probability of a wind blowing smoke down a flue from the next flue. Mesh screens on the caps will keep beasties from dropping in for a visit. While you're up there, caulk with silicone any gaps in the masonry, to prevent future rainwater from freezing and flaking off the masonry.

 

[maccrazy2]

They are fairly close together. That is why I was looking at the larger type setup