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50juan 04-21-2010 05:34 AM

Sizing and installing Ductwork.
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Hello, I have a home that is less than 1000 sq ft. Single Story in Oregon. I have decided to take the task of installing a split air system. I want to first intall the air handler w a 10kw heat element( lack of $$) then at a later time add the condenser. From what I have gathered I purchased a handler 1.5-2 ton this one>
Im perrty handy but can anyone point me in the right direction to get started with the ductwork. I was thinking of running it through the attic, but unsure.. Here is an image of what I thought.. Any ideas would help..

beenthere 04-21-2010 06:07 AM

Running it through the attic is ok. You'll want an R8 insulation value on your duct.
The trunk line looks to be too long for a non reducing trunk line. It may be that you just aren't showing the reductions.

Past 24' you can have some troubles with velocity. Pass 28' you will have trouble with velocity, and lack air at the supplies nearest the air handler.

I use to install the Gibson line. Which is the same as the Frigiidaire.
There ok units. But, the blowers are small on them. They have poor performance on small duct systems.
So duct systems installed by rule of thumb end up with very low air flow.

The unit you selected. Having a VS blower. Will end up using more electric then you will like, if the duct work is undersized.

Also, your tapping off of a supply branch to feed another branch doesn't work very well, and should not be done. The pennies you save by doing it, will come back and bite you in the end.

50juan 04-21-2010 07:31 AM

Thanks for the assit.. I was thinking.. the home has a total length of about 45ft. I was thinking of using 20x8 rect trunk line then at 20ft reduce it. I just don't know to what size.. Should I upsize the trunk.

Point taken on the tapping into branch. Will not do. :thumbsup:


beenthere 04-21-2010 08:01 AM

The 20X8 should be ok.

After you attach supplies equaling about 200 CFM. Drop it to a 16X8. Then after attaching supplies for 250 CFM to the 16X8, drop it to a 10X8 for the remaining CFMs.

This will maintain a reasonable velocity. And also keep your static from being too high, in the supply trunk line.

This is based on your longest supply TEL being less then 200'. And your return TEL being less then 150'. By your drawing, your supply will be somewhere between 160 to 200'. And your return if straight through the wall and into a horizontal return air box under the air handler, should be very close to 150'.

50juan 04-26-2010 05:49 AM

Since you used to install these air handlers. Do you know a place where I can purchase the return and supply plenums. I have not really researched the return, but the Supply one must be odd size at 12 7/8 x 18 1/4.

Would you be willing to walk me through my slow moving install process via pics and ?? like my advisor. :laughing:

beenthere 04-26-2010 06:27 AM

For your return air box. #394-19.

Supply plenum #99U162030.

Thats a 16X20 plenum. The sides get bent inward. So that the plenum is supported on the sides, and is fastened on the front and back by screws.

Both the front, back and sides should be sealed to the air handler with caulk or mastic.

I can help you if most any question you have about installing it.

The supply plenum I listed is sheet metal. If your using duct board duct in the attic. You just make the supply plenum from duct board also. And make it the dimension you need for your air handler, and transition it to the size you need for the supply duct to attach to it.

50juan 05-15-2010 11:22 PM

continued WORK..
3 Attachment(s)
Hello, its been awhile since I have done any work on my HVAC. I've been occupied with building guns instead.:yes: Any way I removed air handler from box today and placed it against wall were I plan on putting it. I installed the heat element, but can not figure were the leads mount. It has a bracket where the current must attach, but where does the bracket attach.. Im jumping ahead a bit, but figured I'd try to find out.. Here are some pics..

beenthere 05-16-2010 05:47 AM

Not sure on that air handler.

But, the install instruction will tell you.

50juan 05-29-2010 02:32 PM

duct seleection
2 Attachment(s)
Question for you. Yeah another:no:. I have air handler palced where it will be- Horizontal- and plan on runnig ducts through attic. My concern now is with the plenum. What would you advise I use. The pics show what I mean. Thanks

beenthere 05-29-2010 02:43 PM

The ell is better. And if you use turning vanes in it, it will be better yet.

50juan 05-29-2010 02:56 PM

Im guessing by ELL, you mean the second pic with the curved plenum.


beenthere 05-29-2010 03:29 PM

Ya, the second pic.

Your welcome.

50juan 05-31-2010 05:38 PM

besides the vanes, do reccomend the plenum to be insulated or any other reccomendations.

beenthere 05-31-2010 06:07 PM

If the room its in isn't conditioned. You want to insulate it. Even if it is conditioned. Might want to insulate/wrap it. For those times/days that you set the thermostat back. And the humidity gets high. The plenum would sweat some at first until the humidity came back down.

You need an aux/secondary drain pan under it. Its code. Anytime a leak could cause damage to structure. A secondary pan is required. Might want to install a wet switch in the pan. Shuts the A/C down so as not to cause problems/over flows if secondary pan's drain is clogged.

50juan 06-19-2010 03:34 PM

on my way again.
3 Attachment(s)
I got excited that I've gotten this on what ya think so far.

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