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Old 01-26-2010, 10:59 AM   #1
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dual supply runs for zones?


OK, I need some expert advice on how this should be done...

I want to zone my basement from the rest of my house... basically two zones, upstairs (2 floors) and basement... I originally was thinking put circular zone dampers on each of the runs to a register... but that came out at 25 dampers *aaaaaaggh!* and ontop of that, I assume they would have to be "accessable" since they are hard wired 24v lines and we had plans to drywall our basement ceiling. This would of hid all them basically and made them inaccessable.

since 25 dampers would be $,$$$ just for the dampers... I was thinking maybe it is cheaper to have two rectangle dampers put on the supply...

right now we have one 20x8 supply running the length of the house, and everything branches off that... would it be better to have two supply's one larger one for the upstairs and one smaller one for the basement and have rectangle dampers on them in the furnance room where it will be unfinished basically forever? they would be accessable... and would be a LOT less money in the end...

what is your opinnions? Our house is 2,500 sq ft above ground and about 1,600 below (conditioned space) and right now all that is being fed by a single 20x8 supply with manual dampers on the branch lines (6" insulated R4.2 flex duct)

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Old 01-26-2010, 02:54 PM   #2
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dual supply runs for zones?


Yes, you could do it that way also. I don't know how much cheaper it would be to build 2 new trunk lines and have them installed. Thats the way I have my zone system and it works well and the dampers are accesible all the time.

Either way you go don't forget to install a by-pass for the extra air and the needed sensors.

Sizing the ductwork properly is critical to make any zone system work right. Make sure you plan before you install.

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Old 01-26-2010, 02:55 PM   #3
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dual supply runs for zones?


Yep.

And you system will appreciate it also.

Don't for get. You will need a bypass for when only the basement is calling.
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Old 01-27-2010, 08:36 AM   #4
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dual supply runs for zones?


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Yep.

And you system will appreciate it also.

Don't for get. You will need a bypass for when only the basement is calling.
When you say bypass, what exactly do you mean?

Do you mean bypass that zones supply line back to the return line?

Last edited by BlueBSH; 01-27-2010 at 09:03 AM.
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Old 01-27-2010, 09:12 AM   #5
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dual supply runs for zones?


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Yes, you could do it that way also. I don't know how much cheaper it would be to build 2 new trunk lines and have them installed. Thats the way I have my zone system and it works well and the dampers are accesible all the time.

Either way you go don't forget to install a by-pass for the extra air and the needed sensors.

Sizing the ductwork properly is critical to make any zone system work right. Make sure you plan before you install.
You mention needed sensors, what other sensors are in a zoned system besides the thermostat per zone and the outside temp sensor and/or supply temp sensor? The system I am looking at is basically this one http://www.alpinehomeair.com/viewpro...ctID=453059062

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Old 01-27-2010, 10:46 AM   #6
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dual supply runs for zones?


That looks like it would hae what you need.

The by-pass would go between the supply and return and is sized to hande the leftover air of the total system minus the smallest zone. The air needs someplace to go.
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Old 01-27-2010, 11:00 AM   #7
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dual supply runs for zones?


Is there any guides out there or website calculators that can help calculate demand on a furnance for heating spaces? I want to check to see if the furnance I have is too big or not for the space that is conditioned... they put in a 125,000 btu furnance and it seems like it's just not performing like it should...

anywhere the furnance would list how many CFM it puts out in air flow, or anything else I would need to figure this out? Would like to look at it myself before I call in the pro's if I would need them

I calculated it out to 1,875 cfm going by its a condensing ufrnance at 125,000 btw... but how can I check the duct is sized properly?

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Old 01-27-2010, 01:21 PM   #8
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dual supply runs for zones?


You would need to do a manual J for your sizing and a manual D for duct sizing.
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Old 01-27-2010, 01:44 PM   #9
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dual supply runs for zones?


HVAC Calc its a load calc program.
Worth its 49 dollar fee.

If your supply or return duct is rectangular, and has only 240 sq in cross section less or less. Then its probably under sized.

Yes. Bypasses air from the supply plenum back into the return.

That is a good zoning kit you posted to.
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Old 01-28-2010, 01:54 PM   #10
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HVAC Calc its a load calc program.
Worth its 49 dollar fee.

If your supply or return duct is rectangular, and has only 240 sq in cross section less or less. Then its probably under sized.

Yes. Bypasses air from the supply plenum back into the return.

That is a good zoning kit you posted to.

well the main supply duct that runs the house length is 24x9 (or 8) I think and the return is smaller in size.... so thats what 192 sq inch at the smallest size? (i need to measure it again, i cant remember if its 20 or 24 but its arond that size)

How is the bypass sized? Is it what ever is left over in CFM that has to be returned? say I have 1,875 CFM coming out and I am using 1,200 CFM in the 1st and 2nd floor... I need a bypass duct for that zone that can return the last 675 CFM back to the return?

I also have a humidifier on the supply with a bypass to the return that has a 6" diamater flex tube insulated... how would that factor into the calculations? its only open in the winter

this whole calculating CFM for a house intrigues me

Last edited by BlueBSH; 01-28-2010 at 01:59 PM.
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Old 01-28-2010, 02:01 PM   #11
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dual supply runs for zones?


The bypass must be able to bypass all the air the the smallest unit doesn't use when only it is calling.

So if your furnace/air conditioner needs to move 1875 CFM. And your smallest zone by itself only needs/moves 400CFM. Then the bypass must allow 1275CFM to flow through it.

Humidifier doesn't get counted. Since it should be closed in the cooling mode.
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Old 01-28-2010, 02:03 PM   #12
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dual supply runs for zones?


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The bypass must be able to bypass all the air the the smallest unit doesn't use when only it is calling.

So if your furnace/air conditioner needs to move 1875 CFM. And your smallest zone by itself only needs/moves 400CFM. Then the bypass must allow 1275CFM to flow through it.

Humidifier doesn't get counted. Since it should be closed in the cooling mode.
Awsome, thanks! You guys are a big help!
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Old 01-28-2010, 02:25 PM   #13
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dual supply runs for zones?


Well with all this sizing talk, I starting wondering, is my filter box the right size?... right now this furance when they put it in used the old return boot... well that has a filter box for a 16x24x1 filter and right now it has a 3m pleated filter in it.. http://www.amazon.com/gp/product/B00...ef=oss_product this one to be exact... is this hurting my furnance blower or furnance in anyway or add to the list a new return boot and filter box?
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Old 01-28-2010, 02:28 PM   #14
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dual supply runs for zones?


Use a general purpose pleated air filter.
One that isn't made by 3M. They are TOO restrictive.

It si making your system run hotter in heat mode. How much? Can't tell from here. Also causing low air flow in cooling mode, which could cause liquid flood back to your compressor.
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Old 01-28-2010, 02:32 PM   #15
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dual supply runs for zones?


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Use a general purpose pleated air filter.
One that isn't made by 3M. They are TOO restrictive.

It si making your system run hotter in heat mode. How much? Can't tell from here. Also causing low air flow in cooling mode, which could cause liquid flood back to your compressor.
Alrighty, thanks for all the info... was trying to figure out why my nat gas bill was outragiously high the past couple months (this is the first year in this house) and its all starting to make sense now... you've been a REALLY big help! any filters out there you would recommend?

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