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Old 11-02-2008, 08:01 PM   #16
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Help! =)


What are the sizes of your trunk lines and what is the GPM of your furnace?

Going one way, My trunk line sizes are:8" x 16" x 22' (maybe 23') w/ 7 separate supplies, one branches from another (the small kitchen supply) so 8 total. The other way; 8" x 16" x (approx) 8' with 4 separate supplies

All supplies are 6"

As for the GPM of my furnace, I'm sorry I do not know/understand what that actually means. Could you please explain? The furnace is a Heil, model number 9MPD075F12C. I looked in the manual but did not find any relevant information about the GPM for this model. But I will add this:
Blower Data:
Type /Size: 11-10
Moter amps/RPM: 8.0/1050
Motor type/size: PSC/.5hp

Maybe that might help?

For a simple test, defeat the furnace blower door safety switch with a piece of tape. (keep children and small pets out of the furnace room with the door off) With the blower running check the air flow at the supply outlets with the door on and with it off, is it better or worse?

-That might be above my knowledge to complete, I guess I'm in over my head here with this problem of mine...some DIY person I am..=( If you could explain a bit I might try it or I will ask the HVAC person about this though.. Thank you.
(Bonus question; Why do I need to keep children and small pets out of the furnace room? I keep imaging them getting sucked into the furnace...lol)

Thanks a bunch everyone!


Kieran

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Old 11-03-2008, 09:12 AM   #17
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What I was looking for was to see if with the blower door off you would get better supply air in all the rooms upstairs. Keeping your pets and children out of the room keeps everyone safe!
If you remove the furnace door when the furnace is running a door switch should kill the furnace. It will be a small switch somewhere around the outside of the door. put a piece of tape on this switch so the furnace stays running allowing it to suck air from the basement, check your supply's and see if they are moving more air or not. If they are you need more return air!
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Old 11-03-2008, 09:29 AM   #18
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My bad. I have been plumbing all week and had my plumbers hat on and was thinking GPM. There's no GPM's in forced air furnaces.

What I meant was CFM's. Yea, that's the ticket.

Well it looks like your ducting and feeds are fine. A little undersized but not way out of line.

You should be able to feel the air coming out of the vents when the furnace is on and this part baffles me. You say there is no leaking in the duct work. The vents on the floor are open. They furnace goes on. Your ducting is a little small but workable and should increase air velocity making it easier to feel???? (thinking aloud here seeing if I missed anything).

Unless the furnace is about 800 CFM's????

Well at this point I am at a loss.

So I am back to my original question. Does your house feel warm? If there is heat and cool and the house feels comfortable then I would say the system is working.
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Old 11-03-2008, 09:54 AM   #19
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Quote:
Originally Posted by 1610 CUB View Post
What I was looking for was to see if with the blower door off you would get better supply air in all the rooms upstairs. Keeping your pets and children out of the room keeps everyone safe!
If you remove the furnace door when the furnace is running a door switch should kill the furnace. It will be a small switch somewhere around the outside of the door. put a piece of tape on this switch so the furnace stays running allowing it to suck air from the basement, check your supply's and see if they are moving more air or not. If they are you need more return air!
It should also be noted that this is only for testing. If you leave it off your A coil will fill up with dust and make you system useless till it gets a thorough cleaning.
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Old 11-03-2008, 07:27 PM   #20
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Hello again and good evening!

Marvin Gardens
,
Thank you for taking the time to respond.
I found a graph in my manual about CFM of my furnace. But I don't know the speed tap (?) or what speed the blower is on..(hi, med hi..etc)
Well it looks like your ducting and feeds are fine. A little undersized but not way out of line.
-What size should the trunk line and supplies be then if they are a bit under-sized?

You should be able to feel the air coming out of the vents when the furnace is on and this part baffles me.
- I can feel the air coming out, it's just very little air. On some of my registers not even enough air to move a cotton ball. (or to make it shake a bit)

You say there is no leaking in the duct work. The vents on the floor are open.
-No leaks that I could see, nothing major anyways.. and yes!, the vents are open..=) {I know you had to ask, tough questions some times have the easiest solution..}

Does your house feel warm?
- Not really=(


1610 CUB,
Thank you kindly for responding.

I did as you instructed and yes I did have a bit more air movement through the supplies, not a bunch mind you but more!

So, if it is a return air issue, should I add more lines for RA or increase the size of existing RA's? Or should I be looking at increasing the trunk line size and supplies?... OR both??

Thanks and have a wonderful evening!!

Kieran

Last edited by Kieran21; 11-03-2008 at 07:32 PM.
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Old 11-04-2008, 09:50 AM   #21
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I would look at getting a 8 or 10 inch pipe into into the rooms with the most problems.
Size wise your S/A is o.k. but the R/A is way short. If you use your walls remember the best you can do is 3.5x15 or 50sq/in. 50sq/in is only good for 250cfm @ 700fpm thats not very much. I hope I have helped

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