how to increase airflow to second storey - http://www.hvacmechanic.com/ Forums
Original message
| chris_s
 |  "how to increase airflow to second storey"
, posted Mon 28 Apr 10:03  
Hi,
I have a two storey home (with basement) in south central Canada.
I have found that during the winter, my second storey is difficult to keep warm, and in summer my second storey is difficult to keep cool.
I believe that the problem is because the main trunk for the vents runs from one side of the basement (where the furnace is) across the house, up the outside wall on the opposite side of the house from the furnace, then back across the floor of the second storey. Basically it's a very long run, and by the time it reaches the end (bedroom on the second storey) there just isn't much air pressure left. There is a return duct in every room, so I don't believe that is a problem
Now, one HVAC company around here told me that the only real thing that can be done to improve this situation is to install a new more direct trunk directly up from the furnace to the second storey. Basically a major renovation job. I'm not planning on keeping this home for more than another 3, maybe 4 years, so I don't want to commit to this much work.
However, I'd be open to some more basic changes.
Would it be possible to change pulleys on my fan motor to run the blower at a higher speed? The furnace is natural gas, and it has what I believe is called a centrifugal blower that is belt driven by an electric motor.
I'm open to suggestions, hopefully I've described my problem well enough for everyone to understand!
thanks
hack mechanic please forgive my noobishness!
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Replies:
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| mechacc
| "Re(1):how to increase airflow to second store" , posted Thu 1 May 06:43
Who knows. Someone may have installed a generic replacement blower motor setup with the wrong rotation.
Another possibility in upgrading the flow might be is if the takeoff runs from the trunk duct are straight ones is to install tapered takeoffs. That is takeoffs that have a larger opening than the existing pipes then reduce down to the size of the existing pipe.
MechAcc
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| chris_s
| "Re(1):how to increase airflow to second store" , posted Wed 30 Apr 14:36
Thanks for the input everyone!
I am going to check out the furnace innards to make sure there is no obstructions there
Installing a new trunk unfortunately isn't something that my home layout lends itself to, at least not easily.
Now, if I were to install a booster fan, the easiest place for me to put it, on the only trunk that goes up to the second storey, would be in a horizontal running section, which would blow the air into a 90º bend going upward (and another 90º to go horizontal across the second storey floor)
Will these 90's kill my airflow enough to make it a bad idea? I haven't yet reviewed the schematics for the house yet to confirm the location of everything, but there may be a spot where it could be installed on the second storey horizontal section (but then the air feeding to the booster fan would still be going through the 90's, so...)
I'm just rambling aloud, if anyone has more advice it would be appreciated! :)
hack mechanic please forgive my noobishness!
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| | dwcaveney
| "Last chance-- see 13 and 14" , posted Wed 30 Apr 20:29:
1. get a duct test. (might have a disconnect)
2. find available static pressure, external static pressure (on blower), size of furnace BTU, blower CFM, total effective length of duct work, operating point (where fan curve crosses duct curve, your system is categorically non-operational), house size, heat and cooling loads.
3. once you tell us that, we can design a fix for you over the internet.
4. HOWEVER, once you know the system information, we won't have to design a fix for you because you will be able to do it your self.
5. has the system always functioned this way?
6. a good tech with a Duct Blaster can give you an overall leakage rate. He can then pin point a disconnect in most situations by leak testing between registers, plenum, and returns. (but it won't work because your duct system, as described by you, is worthless)
7. overall leakage in an average home is between 20% and 35%. if you have a disconnect, you're toast, if not willing to pull sheetrock off and fix. (that means when you fill up your car and pay for 15 gallons you are only getting 10)
8. the duct blaster operates at 25 pascals (1/10 inch water column) about 0.00361 PSI. it cannot damage your system.
9. if your house was built before the new duct tapes UL 181 and mechanical connections you probably have a worthless duct system unless you fix it. And fixing it is doing what the guy, who looked at your house, told you to do. I gave you an alternative in my other post, which I have deleted.
10. the return air in every room is also a problem, because the duct length adds a huge pressure loss to the system. "installer" thought he was building some type of circulation loop, fact is, he just didn't know what he was doing.
11. yes 90s will "kill" air flow, every fitting and configuation has a duct length equivalent; for instance a 90 branch take off fitting at supply trunk adds 65,75,85 duct feet respectively when the number of downstream branches is 0,1,2.
12. thank God, it's spring time, you got a couple months to think about it.
13. you might try connecting the the return ducts to the supply side of the furnace and replace CAR with one large.
14. from an operational standpoint the location of return air grill and duct work (if sized correctly), means absolutely nothing. (i hope you know it has locate in the conditioned space)
15. i have found that when you tell a furnace to fix itself, it won't.
16. yes, you can turn the fan up with the speed taps on the motor but more air will lower the split(delta T). So if you get any more air it will be cold.
17. TEST: disconnect the return air system at the FAU, run your furnace without it, and you'll see what i mean. please be safe when doing this and don't run it very long cause you'll be backdrafting your CO and NOx gases. Get your buddy to help you and send the wife and kids to the store.
18. when you get more upstairs air, email me 1K.(just kidding)
Good Luck
DW
[this message was edited by dwcaveney on Sun 4 May 10:58] |
| deanmando
| "Re(1):how to increase airflow to second store" , posted Mon 28 Apr 16:24
Your problem is very normal, with one exception. You mentioned its dificult to keep second story warm in the winter, this is uncommon. But the hot upstairs is normal.
Essentially, you have already dignosed the problem, air will flow to the easiest places posible and also proportionaly according to that ease. So, the more restrictive the leat amount of airflow.
You can overcome this a few diferent ways.
1-Install a second system in the attic for the upstairs only. This is your most expensive option. However, its one you may wish you had persued after trying the lesser options and they dont work.
2-Retrofit the ductwork in oreder to zone the upstairs and the rest of the house. Uses moterized dampers to automaticaly stroke and supply air where its needed most. This is not a bad option except that the retrofit of duct is often involved and expensive. Also can be very noisy depending on the size of the zones.
3-Booster fans. These little buggers get installed inline with your branches requiring a boost. This is your least expensive option for a reason. First off, dont buy the little tin deals at home depot. They sound like model airplanes and dont move very much air (inspite of the brochure). So buck up and buy a nice centrigugal inline fan, (6" is about $130). To be effective, need to install them in every branch run feeding the upstairs. Can be wired to come on on call for cool or heat or both, up to you.
Anyways, you may screw around with option 1 or 2 only to spend "x" amount of dollars wishing you had put them towards option 1.
Dean Mando
"Words are wind actions speak volumes."
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| acefurnacefxr
| "Re(1):how to increase airflow to second store" , posted Mon 28 Apr 15:31
adding zone controls is the best option
HVAC REPAIR IS NOT A DIY WEEKEND PRODJECT
I have been performing HVAC repairs for 23 years
http://www.hillaryclinton.com
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| | chris_s
| "Re(2):how to increase airflow to second store" , posted Mon 28 Apr 16:51
did a bit of reading up on zone controls, it's quite fascinating. I am an IT person by trade, and love gadgetry like that.
HOWEVER, in an existing two storey home with drywalled ceilings on every floor (no access to 99% of the ducting) it's just not going to be practical to install dampers and wiring.
As it stands, I have every duct grate on the main floor and basement levels closed off, to try to encourage air flow to the ducts on the second floor. It does push air to the second storey, but not a whole lot.
hack mechanic please forgive my noobishness!
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| | mechacc
| "Re(4):how to increase airflow to second store" , posted Tue 29 Apr 17:14:
Check and make sure that the blower assembly, evaporator coil and if high efficiency furnace the secondary heat exchanger coil are clean.
Get a technician that is able to measure the furnace static pressure and airflow.
Anything is possible. Have seen an install where the evaporator coil platform had an opening only half that of the evaporator opening.
MechAcc
[this message was edited by mechacc on Tue 29 Apr 17:15] |
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