Airflow / cold air return

[robroy]

I have a new home with a Carrier Infinity 96 gas furnace and I'm concerned about improper airflow. For the supply, people tell me that on HIGH, it should be enough to really blow your hair noticeably -- mine doesn't out of any register. For the return, I did the "paper test" by placing a piece of paper over the return register - some have some suction but not enough to hold the paper fixed, some have NO suction whatsoever !! Are these tests enough to go back to my contractor with? What "rule of thumb" tests can I use to determine if I have adequate airflow in/out of my supply/return registers ?? ...something I can take to my HVAC contractor! Thanks!

[coco]

hope u have clean filters, start by reaching hand in register to see if a damper is closed inside the run. returns wont be dampered. probly just a bad run, not smooth, sharp bends etc. if u have access to duct make sure those returns didnt become disconnected. possible inside a/c coil packed w dirt?

[robroy]

Yes, I've covered off all the obvious stuff. Actually, I've tried to tune the ducts/airflow through the use of dampers, without much noticeable success in airflow / home comfort levels.

[docholiday]

As for the system, it cares only about what airflow is going through the unit. A properly designed duct system is another thing. You may simply have oversized ducts. I have never heard of a system that is supposed to blow your hair in a home. Where I come from that would be a problem. Did a contractor tell you this?

My first question would be is the home comfortable and then is the home evenly cooled and heated. If so, then I wouldnt mess with the system. If it isnt, then maybe it should be examined.

[bryancorfu]

I read in a text book from school, that if sytem is installed correctly you shouldn't know its running. The theory is that you wont haer or feel air movement when sytem is on. It will bring house to temp. without you knowing its even on. If your house is staying at your desired temp, then I wouldnt be concerned about how much air is coming out of registers. If its not coming down to temp. then theres a problem.

[bryancorfu]

You would also know if airflow is noy enough, if your evaperator starts to freeze up. After system is running for a while, check large line with insulation on it, and see if it has a coat of frost on it where it enters your evaperator.

[Irishmist]

This is exactly why you don't see any bald techs. The h"air"flow technique for determining proper air distribution is a tried and true method. This is why your very best service techs have a full flowing mane of hair. NOT.

[davidr]

Originally posted by bryancorfu
You would also know if airflow is noy enough, if your evaperator starts to freeze up. After system is running for a while, check large line with insulation on it, and see if it has a coat of frost on it where it enters your evaperator.

I would not depend on this as a test to determine if airflow was low.

[bryancorfu]

Thenks for that link, davidr. I just started in this field and am going by what Ive learned s far. Any info or new reading material is appreciated.

[robroy]

Sure, the system adjusts to set the temperature according to the location where the thermostat is, but this hardly is satisfactory if there are large gradients throughout the home. THIS, HOWEVER, IS NOT REALLY ABOUT TEMPERATURE, but rather achieving the recommended # of air exchanges throughout each room of the house (perhaps I should have posted this to Indoor Air Quality forum ..Ooops!). Thanks!

[davidr]

bryan,NCI has some great downloads on how to measure & interpret static pressure readings.
This is the best way to determine a fans airflow.

[robroy]

One thing I do notice is that the original installer definitely uses a lot of the joist work to channel the return air flow -- I thought this was not allowed i.e. building code does not allow use of building structure (???) since it is not intended to provide a proper air seal.

[robroy]

Originally posted by bryancorfu
I read in a text book from school, that if sytem is installed correctly you shouldn't know its running. The theory is that you wont haer or feel air movement when sytem is on.

Who wrote this textbook? Come on ... with my fan on at any speed, I certainly expect to be able to feel airflow coming from the registers. But I agree about the hearing part ... the Infinity 96 is quiet for the most part -- better be since it's supposed to be the quietest furnace on the planet!

[billygoat22]

I met up with an engineer a few weeks ago that subscribed to the "high" school of thought. I ran a pitot tube check at the return duct and reset the airflow for the required cfm by units chart( Trane has the required cfm on the charging chart).
He gets bent out of shape because the airflow is less (much more correct than before) and that his other unit blows a lot, and this unit was on high before, and HE DON"T CARE WHAT TRANE SAYS to set the airflow at. Because hes an engineer and knows it should be on hi.

If the airflowe is right at the unit, and you don't have duct leakage, you won't neccessarily feel airflow x distance from the registers. If you cranked up the flow just to be doing it, it would throw off the system from proper operation

Bryancorfu-The idea of not feeling/sensing the a/c operate is aslo called "transparency".

[dash]

Do you have the Infinity Control?


What model #'s,furnace ,coil ,outdoor unit?

Size of the home?

Newer homes are often better insulated,have better windows,etc..This will reduce the size of the system and air flow required,so their can be a lot less air movement then in your previous home.

[robroy]

Originally posted by dash
Do you have the Infinity Control?
What model #'s,furnace ,coil ,outdoor unit?
Size of the home?


Yes, I have Infinity Control.
Furnace: 58MVP080
A/C: 38TDB037
Coil: ??
Also have a separately-ducted ERV: Venmar AVS Duo 1.9

Home is 2400 sq.ft. with 9' ceiling in bsmt & main floor. Basement is cold, main floor is comfortable, 2nd flr. is warm.

To cut down on heat, I was actually thinking of applying a tinting film to windows (says it cuts down ~60% of heat, as well as provides UV protection). This I would think would help with cooling my 2nd flr, and lower my energy costs.

[dash]

Your second floor has all or most of the attic,so the cfm required per sq ft there is likely higher then the other two floors.




Your best bet would be a zoning system,Infinity as weel ,if the duct work can easily be adapted.

Manual dampers,one per floor adjust by the season,can also be effective,again if the duct system can easily be adapted.


With the Infinity control system,you can be certain it's moving the correct amount of air thru the equipment,if not it should have a fault history,in the controoler.

How many ACH were you looking for and how many cubic feetof space?

[docholiday]

Originally posted by robroy
[QUOTE] the Infinity 96 is quiet for the most part -- better be since it's supposed to be the quietest furnace on the planet!

The furnace has nothing to do with the sound of air coming out of the registers, thats a duct design issue. Each register has a designed velocity and volume intended, the ducts (provided the furnace is proper) provide volume and velocity. Poor ductwork can make any system noisy or ineffective.


Originally posted by robroy
One thing I do notice is that the original installer definitely uses a lot of the joist work to channel the return air flow -- I thought this was not allowed i.e. building code does not allow use of building structure (???) since it is not intended to provide a proper air seal.

Nothing wrong with that for the most part as long as it doesnt leak. Return static and velocity always need to be considered.

[robroy]

Originally posted by docholiday
The furnace has nothing to do with the sound of air coming out of the registers, thats a duct design issue. Each register has a designed velocity and volume intended, the ducts (provided the furnace is proper) provide volume and velocity. Poor ductwork can make any system noisy or ineffective.


Doc...my point was that I shouldn't be able to hear any furnace operations through the registers for my particular furnace. However, with less "quiet" furnaces, of course you should be able to hear this as the nature of duct work being like a primitive phone line, will transmit sound quite effectively. I used to play a game with my kids where I would speak into a gap in one of my supply ducts in the basement (opened to run some cables), and they could hear me clear as a bell from a 2nd floor register. This is of course in addition to duct-induced noises.

[docholiday]

Originally posted by robroy
[QUOTE]I used to play a game with my kids where I would speak into a gap in one of my supply ducts in the basement (opened to run some cables), and they could hear me clear as a bell from a 2nd floor register.


I used to play a similar game with mine.... It was "go outside and play, can't you see Dad's busy bleeding down here?"

[coco]

i would start by figuring out wht the return airflow is so weak