Have to get humidity down: glass tops or canopy?

[wickedfrags]

Is a possibility, most likely with olders homes not equipped with powered direct vent equipment. Realistically unless the fan is located in very close proximity to the exhaust ducting, most fans do not draw enough air to reverse the flow of exhaust. That being said, if your pilot light keeps going out, you hay have a problem!

Fascinating about that code issue and the furnace interlock - any idea how many CFM this relates to?

Originally Posted by Delphinus

Need to be a little careful with this .. If you have negative pressure in your house then if there's any incomplete combustion in the furnace or hot water tank, carbon monoxide can be drawn into the house and not exhausted out the exhaust vent as normal. If you have a strong kitchen fan for example, code will require you to interlock it with your furnace so that you can't create a negative pressure in your house. A standard bathroom fan might not be enough to cause a problem but it's something to consider.

[lastlight]

I know when we built a new house last time this one big honkin fancy microwave we wanted would have made HRV a must have...no choice. It had to do with the CFM rating on it apparently. I of course pushed for that one but we chose a smaller microwave.

[Delphinus]

Originally Posted by wickedfrags.com

Fascinating about that code issue and the furnace interlock - any idea how many CFM this relates to?

I find sometimes that "code" must mean "secret code" because it can be a challenge trying to pinpoint what's in code. On the Calgary municipal website though I found a PDF document for "site supervisors handbook for new home inspections" that has this to say:

HVAC Inspection

• Heating appliances operational
• Fresh air intake requirement, grills, registers, and thermostat installation completed
• Principal exhaust fan interlock completed
• All exhaust fans over 180 CFM – require interlock with furnace blower or separate make-up air
• All exhaust fans over 300 CFM – require that the extra make-up air and may require pre-heating before entering furnace duct work depending on site conditions
• Auxiliary systems (i.e. heat recovery systems) in place must be complete and operational
• Hydronic heating systems (if installed) must be complete and operational

Edit: forgot to post the link - here: http://www.calgary.ca/DocGallery/BU/...s_handbook.pdf

I've never quite figured out if code is national or regional or if there's two and regional usually exceeds national standards, or what. But I imagine in this case it will be pretty close to the same in most if not all places. So there we go - looks like 180cfm requires interlock with furnace, 300cfm requires HRV. I did find another site where it was mentioned it's more about not having exhaust gas backflow down the exhaust chimneys and not so much if your furnace has a incomplete combustion or whatever it was I first thought.

[lastlight]

Yeah that totally rings a bell Tony it was 300+ CFM.

Dez runs a fan through his canopy maybe he can pipe in on how he did it.