Warming house by exhausting ducts into furnace return

Has anyone ever tried this? Or does anyone have any kind of experience that would tell me this is not a good idea??

I've got a newer furnace, the auto pilot kind, and it won't start again this year. And the gas burners aren't in front for me to clean or anything, so I'll have to call the HVAC guy. However, it's going to take me most of the next week to have the basement "HVAC guy ready" lol...so after hours of troubleshooting it myself I remembered that in the winter I don't have to cool the grow room because the cold air coming in from outside to cool the hoods keeps the rooms cool enough...but then I blow that hot air from the hoods back outside. Even when it's below freezing the air coming from the 4th hood is warm.

Now, my house has about 12-15 registers throughout it, but only 2 returns. So I've always been under the impression that it wasn't getting enough return air anyways. So I'm thinking I can just cut a hole in the return in the furnace room and either attach the duct to a flange on the return, or just run the duct in it and tape it off really good. The only possible downside I can think of is that when the lights and fans go off at night, that the return might suck in cold air from outside, but there are filters attached to the fans so I'm pretty sure it wont pull any air through if the fans aren't pushing it.

Any thoughts before I try this out today?

Connect it with a Y connector to the furnace exhaust. Regardless of where the air is coming from it is going out the flue

your plenum will be too small to handle new intake, and it will cause back-pressure i think

Thanks for the quick replies, but I think you misunderstand what I want to do Chesus. I want to route the hot air that is going through my reflectors to the the return right before the air gets pulled from the return, so that the hot air from my reflectors isn't being wasted.

Scrog, are you saying that because the furnace won't be constantly running that the air added to the return will cause back pressure? Because I had thought of that, but I figured as soon as the furnace kicked the fan on it would just pull that air in.

I guess another option would also be to duct into the furnace vent so that the hot air from the ducts keeps travelling in the same direction either way??

Thoughts on that Scrog, or anybody?

Thanks!

hey Bro

I let my hot exhaust air from my new DIY coolhood



in to my apartment, and I don't even have to open my radiators in half of it now to keep it warm (remember I run it at night)

so the idea is good enough, dunno it it works in RL with your system tho ?

I just know my spare bed room and connected hallway normally would be pretty cold with out the radiators open at night time ..

watch for condensation inside the return if your grow exhaust is carrying water vapor.

i run my vents from lights right out the side of the grow room wall helps a lot but i have a small apt.if you duct them right don't even have to worry about smell.

Thanks guys. I've been doing the same thing for the last couple weeks and last year, which was to vent right outside of the growroom to warm the rest of the basement. So I figure this should work the same way, I'm just naturally a little hesitant to cut into the furnace duct lol, but I think this is the way to go for sure. And I'm already glad I posted this instead of just doing it, because I think it makes more sense for me to just exhaust the air from the reflectors right into the furnace duct instead of the return, that way if any of the hot air kinda just sits around in there it will be force out right away when the furnace kicks on.

try to make the cut in a place where you can't see it, make it a nice round one if possible or squared and safe the pice, dutch tape and that can almost fix it as new agin later on if you find out it don't work as you like or summer hit us and you want to dutch it out the house ..

best of luck

I can see a few problems here, but an easy answer also. First, don't even think about cutting into your exhaust flu on your furnace. When your fans are off, it could provide an avenue for exhaust gasses to migrate from the flu back through your hood and into your groow room. Lots of CO2 for your plants, not so good for you. Much more importantly, when your fans are on, this could easily set up a back pressure situation in the combustion chamber of your furnace and force the combustion gasses out the air intake of the furnace and into your house. People die every year in the US and around the world, for that matter, every winter from exhaust issues with their furnaces. I realize that you weren't asking for suggestions on how to get the hood exhaust out of the house. I only mention this in case someone else is reading this thread and sees the suggestion about cutting into the flu and doesn't understand the possible consequences. As far as cutting into the cold air return goes it will work. Your cold air return, although possibly too small for your heating system, from your description, should be plenty big enough for hood fans, unless you have a monster fan. The problem I see with using it, is the noise factor. That duct work would work like a stethoscope. You would likely hear the fan noise anywhere you have a duct or cold air return. Might raise some unwanted questions. Going into the heat ducting would present the same issue along with the problem of when the furnace fan was on, it would overpower the hood fan and force furnace air in reverse through your hoods and out your air intake. If you intake outdoor air, you can see the problem. If you intake from inside your room, you are just pushing the hot air into the room defeating the purpose of cooling the hoods. The best answer you've gotten so far is to exhaust into the basement, outside the room. The heat will still radiate up through the floor and into your living space. I would also suggest that if you pull intake from outside, disconnecting the intake and pulling air from inside the house. If you don't, any air you force into the house will force an equal amount of air out of the house through any crack or gap in the structure it can find, therefore wasting your bought and paid for heat. If your basement is getting too hot, cut a new cold air return intake somewhere in the basement away from the fan exhaust and let it pull out of the basement. This should damper some of the noise factor.

droopy107 said:

I can see a few problems here, but an easy answer also. First, don't even think about cutting into your exhaust flu on your furnace. When your fans are off, it could provide an avenue for exhaust gasses to migrate from the flu back through your hood and into your groow room. Lots of CO2 for your plants, not so good for you. Much more importantly, when your fans are on, this could easily set up a back pressure situation in the combustion chamber of your furnace and force the combustion gasses out the air intake of the furnace and into your house. People die every year in the US and around the world, for that matter, every winter from exhaust issues with their furnaces. I realize that you weren't asking for suggestions on how to get the hood exhaust out of the house. I only mention this in case someone else is reading this thread and sees the suggestion about cutting into the flu and doesn't understand the possible consequences. As far as cutting into the cold air return goes it will work. Your cold air return, although possibly too small for your heating system, from your description, should be plenty big enough for hood fans, unless you have a monster fan. The problem I see with using it, is the noise factor. That duct work would work like a stethoscope. You would likely hear the fan noise anywhere you have a duct or cold air return. Might raise some unwanted questions. Going into the heat ducting would present the same issue along with the problem of when the furnace fan was on, it would overpower the hood fan and force furnace air in reverse through your hoods and out your air intake. If you intake outdoor air, you can see the problem. If you intake from inside your room, you are just pushing the hot air into the room defeating the purpose of cooling the hoods. The best answer you've gotten so far is to exhaust into the basement, outside the room. The heat will still radiate up through the floor and into your living space. I would also suggest that if you pull intake from outside, disconnecting the intake and pulling air from inside the house. If you don't, any air you force into the house will force an equal amount of air out of the house through any crack or gap in the structure it can find, therefore wasting your bought and paid for heat. If your basement is getting too hot, cut a new cold air return intake somewhere in the basement away from the fan exhaust and let it pull out of the basement. This should damper some of the noise factor.

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Thanks for the detailed response Droopy. I bring in the cold air from outside to cool the reflectors in the winter so that I don't have to use any a/c in the grow, and then normally I would duct right back outside, but I think it presents a unique opportunity to heat the house as well as cool the reflectors for free.

I see your point about adding air from outside forcing air inside the house to go back out from cracks and whatnot, but I suppose even if it does, it would be room temperature air escaping and the air leaving the reflectors is hotter than room temp. I also have a lot of windows, so I'm sure I'm losing air from the house either way. Also, it seems like another pro that I'd be constantly bringing fresh air into the house every day. Am I missing anything or is there a bigger reason I can't think of at the moment for not wanting to lose any good air from the house?

I also agree with you that exhausting onto the other side of the basement would probably be a better idea than going into the duct leaving the furnace, but it would definitely be a good way to get some heat to my living room, which is usually colder than the rest of the house anyways. I was actually going to cut in and in put the 6" ducting in at an angle, kinda like making it a "Y", I figured that would take care of the issue you mentioned with the furnace blowing air back through the reflectors. That's how I have my portable a/c units ducted and they run well that way. Which reminds me, I ducted my a/c units this summer into the reflectors at the end of the series and back outside, taking air from inside, and it didn't seem to make my utility bill any higher than expected. So I can't imagine bringing in the air from outside could cause me any issues, especially with all the money it's already saving me from a/c and heat.

I'm also glad you brought up the point of the fan making noise in the ducts. I don't want to hear that in the living room, it would absolutely raise questions. But I'm not going to have the inline fan in the same room, it's just outside of it, and there's 8' of six inch ducting that will travel to the duct that blows air from the furnace to the living room, so I'm hoping it won't make any noise if I do it. I could always add on a muffler or get a quieter fan as well.

So I guess I need to decide tonight whether I want to duct it into the other side of the basement, or right into the ducts going to the living room. I'll think about it tonight and do something in the morning. I'm still open to ideas and suggestions from anybody though. But I think it might be cool to do this just to give other people the idea if it works. Cause gas and electricity are disgustingly expensive, and they have a monopoly in most places. And I can't afford fucking solar panels and shit lol.

Slipon said:

try to make the cut in a place where you can't see it, make it a nice round one if possible or squared and safe the pice, dutch tape and that can almost fix it as new agin later on if you find out it don't work as you like or summer hit us and you want to dutch it out the house ..

best of luck

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That's what I was thinking too. The only reason I'm procrastinating and debating the idea is cause I don't want to mess up the duct for no reason. But yea, I'm thinking if I do it I'll go in at an angle from the side so that heat can't be blown back into the reflectors and won't put reverse pressure on the fan. HVAC tape will seal it right back up though in the Spring. I'm gonna sleep on it. Or rather lay awake thinking about it all night in between naps lol.

smoke a fat one and dream about it

Slipon said:

smoke a fat one and dream about it

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Lol. Lately it's been more like 2 fat ones and a few bong hits of kief just to get a couple hours lol. But I shouldn't complain. I'm fortunate to have an infinite amount of pot to inhale and to eat, and I can grow it practically for free. And now that we don't have patients I get to grow food all winter where the girls used to be lol. I'll finally have some White Rhino dry enough to smoke by tomorrow night, this Cheese is good in the evening, but it doesn't do the trick before bed.

I'm pretty sure I already made up my mind to duct it to the living room. Or rather when I wake up in a few hours shivering and the thermostat says 58 again I'll have made up my mind lol. I don't want to cut into the professional ducting from the furnace, but fuck it, my living room gets cold anyways and I only live once.

I'll take pics though if I do it and I'll post how it works out.