Twin or triple wall Chimney systems in low energy homes has been a issue for some time. Installers and architects trying to make a building as air tight as possible and with little or no breaks in the insulated envelope.
So what is the issue? Chimney systems for solid fuel appliances (wood burning stoves, boilers, pellet stoves, etc) all get warm / hot and have the potential to have a chimney fire internally. This can lead to temperatures in excess is 1000 degree centigrade internally.
To keep the property safe manufactures dictate a gap around the chimney system which must be maintained from combustible materials (to stop the building going on fire).
So as the chimney goes through a wall or ceiling / roof the air gap contains no insulation so it effectively means a gap in the insulation envelops of the building. Not the end of the world, right?
As homes and commercial space try to reduce carbon emissions and costs associated with space heating , stopping heat leaking around chimney systems is essential. On top of that we are now more so than ever trying to create air tight buildings with seamless insulation. So how do we achieve it?
There are 2 manufacturers on the European market that have developed products for low energy passive house /building market. Both are tried and tested and we have used both on projects.
The first is Schiedel, a uk manufacturer , who makes our bread and butter twin wall products. They make the protect box kit for their twin wall range.
Second is Poujoulat a French manufacturer who make a air tight kit for a number of there products. Their bog standard twin wall (Therminox).
The balanced chimney system we use for pellet stoves and small boilers (pgi).
A triple wall chimney system , yes triple where the extra gap in the chimney system is used to duct air into the fire box (efficiency) range.
Both of the manufacturers utilise the same idea and effectively do the same thing. They both use a high density wool insulated sleeve, which fits snuggly over the chimney system , this sleeve is located as it passes through the insulated part of the roof or wall to ensure there is no gap in the insulated envelope.
But what about air tightness? As most of us in the construction industry are aware new buildings have a air tight membrane. This membrane is sealed throughout the building around windows / ducts / joints in construction etc.
The manufacturers have created a steel plate with a flexible edpm rubber seal for the chimney to pass through to create a snug seal around the chimney system. The plate also has a rubber seal to the rear so can be sealed to the air tight membrane or ceiling / wall, alternatively it can be taped on the face using air tightness tape . They also come with a decorative wall plate.
We hope this helps people understand how chimney systems work safely in air tight and low energy construction.
Created by Dave Adams. Pictures created and remain the property of Gondwana green heat, no reproduction without consent.
This is not a technical instruction manual , always follow the manufacturer’s instructions and seek professional install help. All information here is subject to change. Always seek up to date technical advise from the manufacturer. This document was created in April 2023.
