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Old 06-22-2020, 03:01 PM   #16
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Re: Mapping Out My Ductwork


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Originally Posted by r.j.olsen0021 View Post
I'm just trying to figure out my trunk size and when to reduce it based on the two drawings I posted with register locations.

Here's what your supply duct system might look like, treat this post as a visual aid only. Green runs denote basement To keep it simple use 4x10x6" round floor boots, they come in angle, straight or end (torpedo). Use 6x10x6" round angle ceiling boots for the basement. All runs 6" round, don't forget to install balancing dampers (especially the bathroom). You can use 14x8 duct if you wind up downsizing your equipment, 16x8 if you keep what you have. You don't have to reduce the duct anywhere won't make much of a difference for this small a space. Err on the side of too much return air. Loads calcs are your friend, the guys here asking for them are on your side.

Mapping Out My Ductwork-layout.png
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Old 06-22-2020, 03:11 PM   #17
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Re: Mapping Out My Ductwork


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All runs 6" round, don't forget to install balancing dampers (especially the bathroom).
Or design it properly and use the right size pipe and register boot for each space of the house based on the heat loss/gain calculation, cfm and required friction rate.

Bathroom may only need 4" and 3x10 register.

Balancing dampers are only for minor adjustments, if a damper needs to be closed 80 to 90% the system was done wrong.
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Old 06-22-2020, 03:42 PM   #18
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Re: Mapping Out My Ductwork


I agree with you, however (and this doesn't make it right) this is a DIY project, the owner has the equipment and the motivation to do the work. Load calcs are not infallible, if you size each run to the gnats ass there is a lot less wiggle room and let's face it, that's probably not a great idea if he is using the equipment he has. Granted a 4" run in the bathroom would probably be adequate, as for the rest of the house, 6" runs with dampers is more than most houses get today. He's not building a shrine to the HVAC gods, he just wants the best he can get with what he has. 6" round runs w/dampers will give him that without dicking around with different size runs, boots and registers. I've seen too many screwed up heating systems based on someones Manual J inputs and oversized equipment. I think overall the OP should allow some leeway (damper adjustment) in his system. What I have suggested will work for the equipment he has. If he wants to downsize the equipment based on Manual J calculations, great, he can then size all runs per your suggestion.
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Old 06-22-2020, 05:00 PM   #19
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Re: Mapping Out My Ductwork


The majority of the cost is in the ductwork and labour (everyone's time is worth something), not the equipment.

If the equipment is incorrect for the house, it should be returned if at all possible - if not, resold and the correct stuff ordered.

It's best to do things right or the house will be uncomfortable and drafty. If it's over the op's head, time to call a pro in.

Putting 6" pipes everywhere is a complete cop out. There's no need to do that.

There will always be tolerances, it's not an exact science, but come on, 6" flows almost twice as much air as a 5".

Also, for cooling, it's bad to use 4x10 on everything especially with floor vents. If room only needs 40 cfm, the velocity will be very poor and the supply air will stay near the floor instead of mixing properly.

----------------------------

Wise to check local permit requirements before doing the job, a load calc, inspections, etc may be mandatory for a new installation.
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Old 06-22-2020, 06:02 PM   #20
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Re: Mapping Out My Ductwork


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What I have suggested will work for the equipment he has. If he wants to downsize the equipment based on Manual J calculations, great, he can then size all runs per your suggestion.

Sounds like we are arguing, but the tone should be taken as normal conversation. My 6" runs everywhere comment is only based on his existing equipment (not all jobs in general or Manual J), other than the bathroom all the runs would provide an approx. base 90 cfm (cooling) that can be balanced up/down a bit with dampers. What does the owner want to do? Until we know that, it's all conjecture.
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duct , duct design , ductwork installation , heating and cooling


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