Re: Introduction to combustion spillage

[Guest guest]

>

> As requested, here is one summary of the issue of combustion

spillage,

> flue gases, depressurization, etc. from the CMHC website:

>

> http://www.cmhc-schl.gc.ca/odpub/pdf/62028.pdf

>

> Don Fugler

> CMHC Policy and Research

>

Thanks for that Don.

I get into a lot of 'heated' debates with a well known American

instructor who teaches combustion analysis and carbon monoxide

issues to heating technicians through the National Comfort

Institute. The TSSA would have a fit over the furnace

tuning procedures he teaches.

But a valid point he makes in his arguments is how useful the smoke

test at a drafthood is. It basically proves that room air is getting

drawn into the flue and that the flue is not backdrafting, but it

does not really prove that products of combustion are being drawn

into the flue and out of the home, or drawn in at the correct rate.

The draw from a flue will seek the path of least resistance and it

is possible that the dilution air in through this path of least

resistance (aka the drafthood), will compete with the products of

combustion. This could lead to carbon monoxide issues.

Some times moving dilution air can entrain products of combustion

and 'drag them along with them', but perhaps it is possible that

this dilution air can function like a ' Marrs air door' at times as

well, in particular in heating appliances with the built in

drafthoods as illustrated in the pdf link you gave.

So with problematic venting in a drafthood appliance that still

passes a smoke test, he is teaching them to block off the drafthood,

and then add a double acting barometric to control the flue draft

and a spill switch.