Does the chimney cap design have any bearings on the efficiency of our woodstove and other ventilation needs?
Hi all,
We need to make a decision about chimney cap design, soon. In the region there seem to be two main designs. More than the looks I wonder about the efficiency:
1) a simple triangular finish, with two flat pieces of terracotta making a triangle (as if you had put two playing cards to make a tent), that sits on the square base of the chimney that sits on the roof.
2) or a square/rectangular base which finishes with single bricks standing on their narrow ends on each corner of this with a flat piece of stone on top (like a little table that sits on the chimney).
after that there are the modern metal finishes in all shapes and sizes. We tend towards the traditional ones but the two are so different in shape we wondered if one will be better than the other efficiency-wise. and apperantly we don’t need to worry about birds or squirells coming in the chimney here in Piedmont (Italy).
We have very high winds often coming from SSW, if let’s say we chose the triangular option would it matter in which direction the open ends are facing?
also we will have 3 chimneys does it matter what type of chimney cap you have for these 3 different uses: one for our boiler ventilation, one for our woodstove – a small Jotul, and one for our kitchen ventilation. The baths will vent with tiny tubes which hopefully get little terracotta fittings.
your input will be much appreciated.
sincerely,
Canan
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Canan,
If the chimneys are designed to industry and code standards (correct flue diameter for appliance, min. 3' above highest roof penetration, min. 2' above anything within 10' horizontally, sufficient separation to avoid recirculation), then they should function well with any cap configuration. A directional cap, such as the "tent", should be aligned to lift prevailing winds.
However, a woodstove chimney should be cleaned at least once a year, and this requires a cap that is easily removable such as a metal cap. There is a large variety of stainless, painted, and copper chimney caps on the market.
Dear Robert,
Thank you for your guidance. May I please ask the amateur's question: what does it mean "to be aligned to lift the prevailing winds? does it mean that the prevailing winds hit the tent wall (so to say)?
thanks for your patience,
Canan
Yes. Lifting the wind can create a negative pressure zone which will increase the draft. Direct, channeled wind can create a positive pressure zone which can decrease or reverse the draft.