Big difference in temps at registers.


  #1  
Old 11-12-20, 09:29 AM
W
Member
Thread Starter
Join Date: Feb 2012
Location: united states
Posts: 92
Received 0 Votes on 0 Posts
Big difference in temps at registers.

Hi All, After 45+ years of home ownership we just moved into our 5th home (new build 3 bedroom @ 1,400 sq. ft.) but it is our first home that is all electric so bear with me. I have a good understanding of the diffs in electric & gas furnaces with the electric not being as efficient or "as hot" so-to-speak, but I want to be sure that our issue is somewhat normal for a electric furnace. The problem is the extreme temp variance at the registers. I realize that registers farther away from the box are gonna be cooler, but I have chosen 2 registers, both right at 20 feet from the box. One register is in the great room (vaulted ceiling), and the other register is in one of the smaller bedrooms. After about 10 - 15 minutes of the furnace running the temp at the great room register is about 90 degrees. The temp at the bedroom register is about 120 degrees. As mentioned both registers are 20 feet from the box. It's understandable that circumstances may dictate a slight diff, but 20+ degrees seems a bit much. Any ideas or is this normal? On a side note:...while the actual furnace is quieter than a gas unit, the air flow from the farthest registers is extremely noisy. I would compare the sound coming from the noisiest registers to that of about a Cat - 1 hurricane....LOL. With the temp differences and the noise....it's almost as though something may not have been done correctly during the install of the unit. Any opinions are welcomed, and sorry for the lengthy post. Thanks
 
  #2  
Old 11-12-20, 10:25 AM
P
Group Moderator
Join Date: Mar 2003
Location: NC, USA
Posts: 25,041
Received 851 Votes on 786 Posts
Does each register have the same length duct? I know you said they are each register is 20 feet away but have you looked at how the ducting for each is run? Is one duct run insulated and the other not? Other than that a leak in the ducting might be the culprit. This would be a good situation for a thermal camera to look for a hot spot where it might be leaking.
 
  #3  
Old 11-12-20, 11:58 AM
2
Member
Join Date: Jan 2014
Location: USA near Boston, MA
Posts: 1,167
Received 88 Votes on 75 Posts
A closed or partially closed damper in the duct or register could cause air flow/temp difference and noise.
 
  #4  
Old 11-12-20, 02:22 PM
T
Member
Join Date: Jan 2015
Location: USA
Posts: 756
Received 39 Votes on 37 Posts
Pilot Dane is right on with his comment on looking at duct length rather than distance. Having said that, I'm more interested in what else the ducts are feeding. I suspect it may be that one duct may be servicing 3-4 vents while another only 1-2.

Most importantly, though, look for leaks or insufficient insulation using an infrared gun.

 
  #5  
Old 11-15-20, 03:36 AM
ferd42's Avatar
Member
Join Date: Jul 2020
Location: United States
Posts: 234
Received 17 Votes on 17 Posts
Assuming 125F AHU outlet temp, you're losing 5F at the BR and SEVEN times that at the LR. Please tell us the duct ambient temperatures: The air temperatures in the spaces through which the ducts are routed.

Alternatively, assuming a 95F AHU outlet temp, you're gaining 25F at the BR's. Please tell us how many thermostats in the home.

"it's almost as though something may not have been done correctly during the install of the unit" - Welcome to my world!
 
  #6  
Old 11-18-20, 08:12 AM
W
Member
Thread Starter
Join Date: Feb 2012
Location: united states
Posts: 92
Received 0 Votes on 0 Posts
I'd like to thank all for your responses and feedback. To answer a few of the ??'S. There is only about 1 ft. difference in the actual duct length of the bedroom and living room registers where the temp was taken. Minimal to say the least. The main duct runs perp under the joist running the full length of the home (more or less) The duct work running from the main duct to the registers runs between the joist (16 " centered) in a standard walk out type basement with no ceiling. There is only 1 register per secondary duct. The ambient temp between the joist surrounding the secondary ducts is around 60 degrees during your average lower mid west (Missouri) fall / winter in a walk out base. Also....the furnace is for the most part centered in the home with maybe a 5 ft. diff from one end of the home to the other. The main duct is 16 inch that narrows down to 12 inch about 8 feet from the bedroom (S) side of the furnace with the 16 inch narrowing to 12 after about 20 feet on the open living area side(living....kitch....etc). The only real difference in the 2 registers in question are that the 90 degree living room duct is coming off the 16 inch portion of the main while the 120 degree bedroom register is coming off a 12 inch portion of the main. This particular duct work has no in line shut offs and I have had the registers in just about every array possible. All answers and opinions are well taken and i'm still open to any suggestions that this latest info may develop
THANKS !!!!
 
  #7  
Old 11-19-20, 02:58 AM
ferd42's Avatar
Member
Join Date: Jul 2020
Location: United States
Posts: 234
Received 17 Votes on 17 Posts
Questions:
1. Is there only one thermostat?
2. Are the main ducts - the ones running below the joists - round or rectangular?
3. If they're rectangular, what are the heights?
4. What do you mean by "the registers in just about every array possible"?

Please post an image showing the AHU (air handling unit, AKA fan coil unit FCU) and connecting ducts, as well as make and model number of indoor and outdoor units (I assume it's a heat pump system).
 
  #8  
Old 11-19-20, 03:15 AM
ferd42's Avatar
Member
Join Date: Jul 2020
Location: United States
Posts: 234
Received 17 Votes on 17 Posts
Single story 1,400SF new construction. Trunk and branch duct system with floor diffusers, but required branch balancing dampers at connections to mains were not provided. AHU at approx. center of unfinished walkout basement. Two 16" supply mains going each way, and reducing to 12" at some point. 90F LR outlet on 16" main connected to one side of AHU and 120F BR on 12" reduced size main connected to other side of AHU. Both outlets are 20 feet from furnace (IE: 40 feet apart). Do I have that right?
 
  #9  
Old 11-19-20, 03:31 AM
ferd42's Avatar
Member
Join Date: Jul 2020
Location: United States
Posts: 234
Received 17 Votes on 17 Posts
Are the mains metal, insulated metal or fiberglass? Are the branches metal, insulated metal or flex?
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: