Where should my last heating vent go?

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Old 01-21-17, 05:31 PM
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Question Where should my last heating vent go?

I know there are all sorts of factors in figuring out how many heat and return registers. I am trying to keep it simple. I have 2 and it keeps the area pretty comfortable. I feel I should add one more as I can always close them off if necessary.

The two arrows indicate the heat registers currently installed. As you can see I have a kitchen where the third one should go. My thoughts are, bad idea to have one directly over the sink blowing on you while you are doing dishes ( sounds annoying). Also, having one ove the stove could be really un comfortable. This leaves me with where the fridge is. I'm thinking of running a duct to a register above the fridge under a cabinet?

Any thoughts? Maybe I am missing something. Open to any and all suggestions.

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Old 01-22-17, 11:23 AM
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First thing I noticed is that the two, and possibly third register are all in the same general area while rooms to the right have nothing. Seems a little out of balance!
 
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Old 01-23-17, 06:15 AM
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IMO you need to back up. How big is your system, How big is the return duct, How big is the supply duct, The rooms that don't have registers do they not need heat, was a manual J done????????
 
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Old 01-23-17, 09:33 AM
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Hi..
-How do I find out how big my system is? Is it on a sticker on the main unit?

-Are you looking for the length of the return and supply duct ?( the return and supply both run the length of the soffit shown in the diagram).

-There will also be one heat duct in the bathroom (room all the way to the bottom left next to the kitchen). and I will using a heat vent in the laundry room ( far top right corner room) that was sealed off from upstairs after a wall was taken down.

- No manual J was done by me. Before I purchased the home a new heating system was installed ( 12 years ago) I have not added to it yet.
 

Last edited by rufunky; 01-23-17 at 09:57 AM.
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Old 01-23-17, 09:55 AM
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There are model BTU ratings on the indoor unit. Model numbers also on the outdoor. Manual j, manual d and manual s load calculations are what's used to design a system. You need a minimum airflow to allow the unit to operate properly, and not die an early death. Is there air conditioning involved here?
 
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Old 01-23-17, 10:07 AM
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I'm trying to find the BTU rating. It is a carrier 58sta090---10114 . No, currently just forced hot air no AC.

EDIT: looks like it is a 90,000 Btu unit 80% AFUE. The house is 1,560 sqft .

EDIT: I added a actual picture of the soffit and the area to give a better idea of it's size.

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Last edited by rufunky; 01-23-17 at 10:45 AM.
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Old 01-23-17, 10:57 AM
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So 90,000 BTU for less then 2,000 sq ft and 2 supply registers? What size are the supply registers?
 
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Old 01-23-17, 11:17 AM
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I havn't placed it yet. I planned on putting one under the cabinet on the far right of the kitchen. It is going to most likely be the coldest area as that is right near the back door and kitchen window. If I have to put another I could put one at the far left of the soffit in the wall but It may pull the heat from the register on that end.


OOPS I read return registers for some reason! The supply registers can be any size as I still have to build 3" extensions for them to meet up flush with drywall. But currently the ones I have inside dimensions are around 7x10.
 
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Old 01-23-17, 12:44 PM
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How many returns do you have planned? And what size will they be?
 
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Old 01-23-17, 01:59 PM
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I planned on putting one return under the cabinet kickplate on the far right of the kitchen. It is going to most likely be the coldest area as that is right near the back door and kitchen window. If I have to put another I could put one at the far left of the soffit in the wall but It may pull the heat from the register on that end.
 
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Old 01-23-17, 06:42 PM
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Your going to need a LOT more then a toe kick return for 90,000 BTU worth of furnace.

http://www.northwestenergystar.com/s...Deck_Final.pdf
 
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Old 01-23-17, 06:45 PM
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You'll also want to keep air speed low, like around 300 FPM. Higher and things get really noisy. Make sure and keep supply static low, such as around .5 as low airflow can damage components. No returns in kitchens or bathrooms.
 
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Old 01-23-17, 06:51 PM
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Sorry, I was only including what is downstairs. Upstairs I have 9 supplies and 5 returns.
 
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Old 01-23-17, 07:11 PM
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Likely need more downstairs. Do you have enough return area to support the furnace?
This furnace will likely be oversized for the load.
 
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Old 01-23-17, 07:19 PM
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Yes, the return runs almost the same length as the supply. Like I stated earlier, I could put a return on the far left wall as well as the far right floor under the cabinet. My only concern there would be that it will have to be half way up the wall so I may be pulling in heated air :/

I am trying to figure out the FPM for each supply. How would I convert CMF to FPM? Do I need to measure the Square foot of the supply trunk?
 
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Old 01-23-17, 08:55 PM
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The velocity will increase as duct size decreases. There are also friction rates to consider but that's where a ductalator comes in.
Starting point is manual d to get room by room airflow requirements
 
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Old 01-24-17, 07:27 AM
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Against code to have a return in a kitchen. You need to do a heat load to size the duct and registers.
 
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Old 01-24-17, 08:50 AM
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The area I am working with doesn't really leave me many other options except for adding one more supply in the kitchen area, one in the bathroom one return at either end or both ends of the soffit.

So at this point I need to just figure out if I should add to it or leave it the way it is.
 
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Old 01-24-17, 09:16 AM
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Im guessing you are dealing with around 2000 cfm your going to need at least 3 returns with 16 in flex on them and a 14in.
 
 

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