Can someone provide some clarification,or point me in the right direction to get a better understand about Canadian Code (specifically in Calgary, AB) with regards to high CFM hood fans?
When we build our last house, we selected an over the range hood/micro combo. We were told that due to the CFMs of the fan selected (it's around 400cfm) installation would be more because Alberta Code required it to be wired to the furnace ventilation fan. I understand the rational behind negative air flow, potential back drafts, etc and the appliance selections were made early on in the construction process before wiring was completed, so we never questioned the advice we were told. And, the hood fan is definitely connected to the ventilation fan - when the microwave is on, or when we turn on the hood fan the ventilation fan on the furnace does turn on.
Now, both my parents & inlaws are in the process of doing kitchen renovations. And they are both looking at hood fans of over 500 CFMs. Knowing how our fan is wired, they have both asked numerous sale people & no one has ever heard of needing to connect a hood fan to the vent. fan. I decided to do a bit of Internet research and I too am coming up with limited advice on whether this is required or not, and more importantly how it's done during a renovation.
Were we given incorrect information which has caused some disillusion in our mind? Or, are people just ignoring the requirement & avoiding inspections?
The bit of info I have found, I believe some sort of 'interlock' is required which would connect the hood fan & furnace fan, correct? What access is required for installation - are they installed at the hood fan location, furnace location or electrical panel? Ie. Both house have fully developed basements, with finished drywall ceilings, so the ability to pull any new wiring from the kitchen to the furnace room or electrical panel location would be near impossible.
I will leave this thread up for the time being, this is not an Electrical code Issue in BC it is covered under the BC Building code and only refers to new homes and the bathroom fan not hood fans in homes.
I think you need a make-up air unit interlocked with the exhaust fan. The design is a mechanical trade problem, so I'm not sure of the rules.
Recently, I interlocked an exhaust fan with a furnace and the furnace had a large duct on the return air side that drew fresh air from outside. They were using the furnace as a make-up air system. A heater was installed in the fresh air duct, because cold winter air can damage the furnace.
Unless your furnace draws air from outside, it won't solve the negative pressure problem.
I've been away from this forum for a while. This similar situation has been a baffling question for me also. When I started in the trade, we had to wire for OTR microwave interlocks in every new home. A few years ago we stopped. Occasionaly we will still wire for an interlock on larger hood fan units. Seems to be up to the HVAC contractor if they are going to install a makeup air setup. Often I just run the wire just in case if its a larger CFM unit. 18/2 is cheep compaired to the cost of fishing and the service call later because the electrician is always at fault when they decide to add a MUA at finishing stage and there is no wiring for it.