One of the issues to consider when adding a range hood, or replacing one, is whether it will cause depressurization problems in the house. If the exhaust flow of a range hood (or any other fan) causes high levels of house depressurization, there are some possible negative consequences:

  1. Backdrafting or spillage of vented combustion appliances, including fireplaces and woodstoves
  2. An increase in radon entry from the soil
  3. An increase of air entering the house from attic spaces or wall cavities
  4. Drafts from the outside

The bigger the fan and the tighter the house, the more depressurization that is likely to occur.

Have you encountered this in your work? Have you seen instances where a newly installed range hood requires some monitoring or the provision of make-up air? What levels of depressurization have you seen created?

Back when I was testing houses in the eighties and nineties, we saw several houses exceed 20 Pa of depressurization. Are we seeing that today?

The gradual disappearance of natural draft appliances (those with chimneys) and the availability of consumer carbon monoxide alarms have reduced some of the dangers.

We would be interested in hearing about your experiences.

Views: 62

Replies to This Discussion

Don,

My concern is one of liability. 

Even with sealed combustion devices the manufacturers (for example) of gas fireplaces have in the "fine print" warnings for potential back drafting with CYA clauses and advisement for MUA...no one reads these but they are there in the manuals.

Then there is the issue of attached garages...self closing doors have to be adjusted to close off against the potential negative pressure but the hardware installers don't know enough to put the house into negative pressure to test the setup. Have seen this a lot with fire doors in high rises.

Also there is the introduction of risk when ownership changes hands and the new people put in "sealed wood stoves" which never are... 

I would suggest most HVAC/electrical and kitchen contractors and the wholesalers they work with who take on the design and installation of these systems fail to appreciate the risks. Likewise for homeowners who have little understanding of this subject matter.

We put in our spec the option for depressurization testing but have a hard time convincing the generals and their clients to  carry this out...too bad because in about 60% of the projects where problems of all types (mainly moisture related) show up...a test would have would have discovered the flaw(s)

Cheers,

RB

Robert,

Thanks for that. It is a significant problem with house ownership changes and the new occupants are unaware of the workarounds. I have been in houses that have been owned for several years and the owners were unaware they had an operating HRV (operating poorly by that time). It is counterintuitive to a new owner to open a window when they operate the range hood, if that is the recommendation made to the previous owner at the time of hood installation.

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