I think the title explains itself. Commercial range hoods or downdraft exhaust are becoming popular in new homes and kitchen renovation projects. You know they look cool or have the ability to hide in the counter top, and man can they suck. Hold your hair piece around some of these because you could lose it. They actually pull so much air out of the house, that they cause very harmful conditions in the home. And I have been conducting energy audits on more and more of these homes lately and leaving with not so happy customers.
The issue that these exhaust units create is that they are pulling so much air out of the home that air has to come back into the home somehow and this is causing standard atmospheric water heaters and the less efficient furnaces that are still in operation in lots of homes to backdraft. So anytime you turn on the exhaust, it actually pulls the combustion gases from your water heater into the home increasing ambient levels of carbon monoxide. And this situation can occur in any old, new, large, and leaky home.
I mention not so happy customers because when I come across this condition, all incentives from the local utility to make efficiency improvements are halted until the back drafting issue is resolved because we don’t want to tighten up a home and make the conditions worst. Although this is not really a green building issue, it is just that green builders and designers who look at how the house works as a system takes these kinds of issues into consideration. Therefore here is a preview of a great article from GreenBuildingAdvisor.com on ways to prevent the back drafting from these high cfm rated exhaust fans that any homeowner, architect, designer & builder/remodeler should read if considering one of these units.
Makeup Air for Range Hoods
If your kitchen has a powerful exhaust fan, it may be pulling air down your chimney or water-heater flue
Most homes have several exhaust appliances. These typically include a bathroom fan (40-200 cfm), a clothes dryer (100-225 cfm), and perhaps a power-vented water heater (50 cfm), a wood stove (30-50 cfm), or a central vacuum cleaning system (100-200 cfm). But the most powerful exhaust appliance in most homes is the kitchen range-hood fan (100-1,200 cfm).
Every time an exhaust fan removes air from your house, an equal volume of air must enter. The air that enters cracks in a home’s envelope to replace air that is exhausted is called “makeup air.” Two trends affecting makeup air are causing increasing problems for homeowners: homes are getting tighter, and range-hood fans are getting more powerful.
So where does a powerful range-hood fan get its makeup air? If the house doesn’t have enough random air leaks around windows, doors, and mudsills, the makeup air is often pulled backwards through water-heater flues or down wood-burning chimneys — a phenomenon called backdrafting. Since the flue gases of some combustion appliances can include carbon monoxide, backdrafting is dangerous. In some cases, it can be life-threatening.
Continue reading the article at GreenBuildingAdvisor.com