is it going to do anything bad to my furnace if i pump 424 cfm into one of five cold air return lines. im guessing that when the furnace is off all the pressure will pump into bedrooms so i will always have a smell issue without good filtration but im mostly just worried about that much air pushing that fast into the furnace. or is it going to be the exact opposite and increase my efficiency by making air move easier. oh ya forgot to mention the reason its an emergency, the gas company has to get in my house for a "line safety check" there also digging some shit up but the main gas lines run into a room where you have to see my grow room to get into so im moving it to a different bedroom and this is my only vent option as windows are all visible from street
you cant exhaust into the attic? or is this a apartment.... can you describe your setup any better? are you using a carbon filter? or ozone generator? ona bucket? anything to mask the smell? are you 100 percent positive that this is a return line? if it is... it should be no problem.. and like you said it will increase your ducting efficiency .. as long as the furnace does does not have a flap that stops positive pressure some how once the furnace turns off... in which case it will start to create leaks some place else..... 50 50 i guess pictures of the attic lines? can you not duct into the attic and attach a carbon filter?
It probably would be OK, but it's possible you would overwhelm your system which would result in all the return air in your HVAC would be coming from your grow op, leaving stagnant air in the rest of the house. Where are you intaking air from? If from the house then it's OK, you're still circulating air within the house, but not OK if your grow is drawing in from outside.
i would never exhaust a system into an hvac b/c even in late flowering stages a filter isnt going to rid you of all the smell.. you are gonna be pumping MJ scented air all throughout the house and that is pretty counter effective. also not sure how much this applies to your system..but if you are effectively running a "closed loop" you are never introducing new co2 into the air and never evacuating o2.. this isnt good for plant health. steady stream of "fresh air" or co2 rich air is quite neccesary