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That works if you are in a warm climate or are providing heat into the makeup air stream. If you are using untempered outside air as your makeup and start dumping 600 cfm of minus 20 air into a space like a kitchen, that space will quickly become too cold to work in. Dumping it into the airflow from a furnace dilutes it and the furnace kicking in will keep the place habitable. Dumping it into another room somewhere else in the house and letting it percolate through to the rest of the house runs a real risk of freezing something in that space.
Blackhat
Bad experiences come from poor decisions. So do good stories.
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I was wondering if that heat loss would be too much too fast but i was thinking that if the make up air flows in from behind the stove then the cold air would be exhausted with little effect the the ambient temperature to the person at the stove. But your saying that it will still be too cold?
Since my hvac does not have an exchange with outdoor air, do I just run this make-up air in a duct to the cold air return duct at the furnace?
Should i make that duct a bit larger so that the air speed slows down before reaching the cold air return?
Ray
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When I install a new system in a new tight home (Especially what I call foam wrap homes), I have Trane engineers design the systems, ducts and ERV (and makeup air) systems. In some cases, these criteria are complicated in order for them to all work properly and be safe.
If you haven't checked your ducting in the attic, you could have enough leaks in the supply ducts that you are already pulling the home in a negative pressure, or perhaps you have return leaks, pressurizing the house? Infiltration from cracks around windows and doors, even baseboards may already be giving you 600 cfm- maybe 1,200 cfm leakage.
You can install just a fan to allow air to enter the space, but it won't be filtered, causing more dust and allergens in the home, as well as humidity or drier air, hot air, cold air.......................... You might as well just open a window.
You may not need 600 cfm- 300 or 400cfm may be all you need.
If I were going to do this job, I'd test/check all the ducting (seal it), perhaps even have a blower door test done (Especially with gas appliances), install a filtered makeup air system to the existing HVAC system per the manufacturers specs and have it inspected or tested if I were to be responsible for it's safe operation. Perhaps I wouldn't do the job if I felt it would affect the homes cooling and heating and comfort without adding more options.
You, the home owner can do the job anyway you see fit- you will be unhappy only with yourself if it doesn't work right and responsible for it's safe operation- I can't do that- including any advice I give you. There's the right way and the other way.
I suggest you seek a contractor experienced with this. Maybe it is an easy job, maybe it is more complicated due to certain conditions. I'm not there and can't see your conditions.
My old house leaks enough that I'm probably good for 600 cfm- a static test would prove that.
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Fair enough. Thanks!
Yeah, I'd be willing to bet that my old house probably leaks enough for a good 600 cfm under negative pressure and I could always just open the kitchen window, but I figured that planned make up air is a better option.
Thanks for the insight to all.
Ray
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If it were me, I'd install that powered damper as close to the outside wall as I could and run pipe to a spot about 8' from the furnace to connect to the return air duct. I would insulate the pipe and about 4' of duct each side of the connection and tape hail out of the joints in the insulation. Then I'd repeat the insulation and tape process again. Wrapping the thing in plastic and taping that wouldn't hurt either. Then interlock the damper to the furnace fan. If it were me.
Blackhat
Bad experiences come from poor decisions. So do good stories.
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Oh yes. Thanks for the reminder on the sealing and insulation!
Ray