Sounds like it's time for a change for the condo board. Old condos that weren't build up to snuff need to be updated. The board need to come up with a solution to allow your appliances to be properly installed. Your exhaust hood cannot share a duct. It needs it's own dedicated vent.

Why do you need a 700 CFM range hood? Do you do a calculation for this amount of air flow? In order to move 700 CFM of air you will need a 12 inch duct. If you can't install a vent of that size they you might as well buy a less powerful range hood. If you don't you will have a noisy range hood will lower air flow than you paid for.

You are considering connecting the range hood to your furnace exhaust? What will prevent the furnace exhaust gas from entering your kitchen? This is a dangerous idea.

Do you have a furnace and gas hot water heater in your condo? If you do then even if you had a dedicated vent you may have back draft issues. The general rule is anything over 400 CFM needs make up air. You need to think about this carefully.

I agree with the other posters and strongly suggest getting a variance from the HOA. Anything other than a proper vent is going to be a compromise and/or cost a lot more money. On the other hand, a well-functioning hood increases the value of the unit, if you ever plan on selling.

If installing a vented hood isn't viable, then look into the recirculating hoods that Vent-A-Hood makes. They aren't cheap, but they are the only model that is known to actually work. It will probably still not quite match an exterior-venting hood, but it reportedly works surprisingly well in general. Also, the nice thing about a recirculating hood is that you won't have to worry about make-up-air. So, that might help with justifying the cost.

For the VAH recirculating hood, you will need to change filter packs very 5 years or so. So, factor that into the cost.

Up creek with no paddle. You can't patch in and safely "share" any of these three things with a kitchen exhaust fan. Maybe it would be feasible to get a ventless dryer and then use the dryer vent for the kitchen hood, but it may or may not be adaptable for that new use

You need some serious advice from an expert.

Don't waste your money on a "recirculating" vent, they are totally worthless. They are a grease trap (and therefor fire hazard), don't do anything for cooking odors, and where do you think all that water vapor/steam goes?

As for Vent-A-Hood ventless hood, note their caution "for LIGHT residential cooking". You know what that means - same as my Jenn-Air downdraft - might as well not have bothered!

“In order to move 700 CFM of air you will need a 12 inch duct.”

No you don’t. 8” diameter is sufficient. @Mike_home - where are you finding homes with 700 cfms hoods with 12” ducts?

You can install an 8 or 10 inch duct if you don't mind the noise and the reduced air flow. The point I was trying to make is the wall penetration required is much bigger than any which currently exists.

My advice is if you can't support the venting size then buy a smaller range hood fan.

Keep it simple... it needs its own vent to the outside - you cannot combine into another vent. You might be able to press the board for a variance, otherwise recirculating is your only option...

Good luck!

mike_home

Your point is correct.

The point I failed to make is that the ducting is supposed to be sized for minimal impingement deposition of grease particulates that aren't captured by the hood filter -- thus the intent of the velocity range specified by NFPA 96. (Also please see the reference below.) In any case, for a duct meeting velocities up to 2000 ft/min, a modest duct length will have much lower pressure loss than the baffles or mesh filters in the hood. (And, I should note, lower noise generation than the blade tip turbulence of the blower producing that velocity.) Hence the duct size does not dominate the volumetric air flow, the hood filtering does in concert with the limitations shown on the hood blower's fan curve plot.

I would recommend against a duct size so large that the actual, not the rated, air flow velocity is below 500 ft/min during grease particulate generation, unless the duct is so short that absolute grease collection is negligible.

Ref: ASHRAE Journal, November 2002, pages 26 - 31, New Rules For Kitchen Exhaust, William D. Gerstler