Any HVAC experts? Want to connect exhaust up to Chimney flue.

All, I have been a cab grower for the past year and want to expand my capabilities somewhat. Today, my cab sits in a utility room that also contains the house furnace and the hot water heater. The cab exhausts into the room through carbon filters and a small fan on the room itself gently exchanges air through a 3 foot passive vent louver.

I am interested in breaking out of the cabinet and expanding my space a bit into my utility room. Both the furnace and hot water heater exhaust gases into a flue that goes up and out through the chimney. The flue is lined. I have a double flue design as my house has a fireplace on the main floor. One flue is for the fireplace, the other flue handles the HW heater and gas furnace.

I am interested in seeing if it's possible to exhaust my grow into and out of the flue. I have done some research, but a friend of mine who's a plumber (but not an HVAC expert) said it might not be a good idea as exhaust gases from the mechanicals could back up if I 'splice' into the existing stovepipes with a 'Y' or 'T' fitting and if I don't use a flapper vent. My point is that since the grow fans are always on, there is no chance for backup and therefore no need for a flapper.

The water heater is a 'draft induction' type where air is drawn into the exhaust and out into a 3" stovepipe through an open manifold. The furnace is direct draft (4" to 5" stovepipe)

Both connect up to the same flue. The HW heater is piped into the flue just above the furnace about one foot...

I can't find my camera, but I hope to post some pics if that helps.

Do I need to cut into the flue masonry? If so, then higher or lower than the other mechanicals? Is there an easier way, perhaps a Y fitting or something? If so, which mechanical should I should splice into?

Not sure if anyone has any similar experience in this regard and can give me some details, photos, or other useful info. Any input would be greatly appreciated.

The issue is odor, you can then smell the flowers outside. Yes I did this, build a scrubber instead.
H

It's extremely dangerous to piss around with venting. First and foremost issue would be, if chimney became blocked, fan from lights would force furnace/tank exhaust back down thru draft hood. This is just my opinion, but I have been servicing/installing HVAC for 30 yrs. and seen many cases where homeowners have caused unsafe conditions by touching things they shouldn't

Haps thanks for the input. I will be drawing through carbon filters to cut down on the smell. I am most concerned with exhausting the hot air into a place that doesn't heat up my room, I am planning on 600 watts and am hoping this helps to disguise the fan noise a bit too.

Smokerman, thanks for the expert opinion. OK, I think I can be talked down from the ledge...I am not going to cut into existing ducting to exhaust my air. Though if you look at the pic below you'll notice my furnace comes into the flue just below my WH, which is draft induction. If one accepts the overpressure when the furnace is on, but the WH is not burning--does that mean that furnace gas can back up out of the draft induction, or is there something here I am not seeing? My thought is that the exhaust from my grow will always be on, I never turn the fans off...

I guess my question is: can I impact drill a new inlet into the flue and exhaust my grow into that or is that just a bad idea? If so, should I drop that in below the furnace? Any input would be much appreciated here.

Can't figure out how to do pics on the new site, but here's a shot of my flue now.

http://www.icmag.com/gallery/data/500/38655IMGP1490-med.JPG

as long as the fan is above all exausts for any furnace or what have you your cool

i just looked at the pic hmmm

i dunno how to do it this way but you need to not ahve any blow back in those exaust vents

i would install a carbon monoxide dectector right there while your doing this to be sure and stay home for like 48 hrs to make sure

Not an expert but I would tap into that furnace pipe with 1 of these if it were mine.

http://americanhvacparts.com/Merchant2/merchant.mvc?Screen=CTGY&Category_Code=duct-saddle_tap_Twyes