View Full Version : Ventilation work for over range microwave/fan

08-17-2009, 09:51 PM
I bought an over range microwave/extractor fan combo for my place. Just wondering if anyone has had to deal with any companies in town that install or repair the vent that goes into your wall and up to the roof.

My vent is off centred from where the opening is in the wall. In order for my unit to work I need to have the vent moved on centre of the opening and made sure its working.

I heard from someone that anything over 300cfm requires a make up unit? Can someone confirm? Apparently its code now.


08-18-2009, 04:36 PM
I dont have any answers for you reguarding moving the venting, but I CAN tell you, that over 300 CFM DOES require a makeup air unit. It is code, and can assure you, by the time you buy a makeup air unit, and pay for its complex installation (wiring and interlock) it wont be cheap..

08-18-2009, 04:58 PM
I think I was quoted $3000 for make up air modification.

08-21-2009, 07:12 AM
I got an HVAC company over to my house and it depends on the CFM rating of your hood fan. The higher the CFM the more stuff that needs to be installed and Lint is right, at least $2000. I'm gonna stay 300CFM and less now.

08-26-2009, 08:46 AM
What are the ramifications for not installing the make up air unit? I understand that you can just crack open a window, but this may not suitable during the winter season. As well, I don't usually have my hood fan at full blast. Aside from that, am I missing the point? :dunno:

08-26-2009, 09:01 AM
Exhaust gases COULD be pulled back into the house. But from what I understand, most bathroom fans are around 100cfm. So this means that you should have make up air if you ever plan on turning on all 3 bathroom fans at the same time as well. Most contractors think it's unnecessary since most homes are not sealed up tight as well, so there will be leaks that air is able to enter the home.

08-26-2009, 09:47 AM
It sounds like the make up air unit is for "worse case" scenarios. For example, if I had all bathroom fans on and my hood fan at full blast, all day long.

How much damage can occur if you had all fans in your house on for 15 mins? 30mins? 1 hr?