Evaluating heating/cooling ducts


  #1  
Old 09-30-03, 10:20 AM
mwolf1
Visiting Guest
Posts: n/a
Post Evaluating heating/cooling ducts

Mine is a complicated question.

I have a gas furnace and central air. I live in a ranch house with a living room in the basement. This winter I am going to finish the ceiling in the basement with drywall. Scoff if you must, but I am willing to forgo accesebility for the asthetics of drywall. I want the room to look like a living room not a basement living room.

Anyway, in preparation of this I am trying to cover all the bases. i.e. What do I want to do before this drywall goes up. My eyes keep lingering on the heat ducts.

The furnace is located to the northwest side of the house. Venting runs away from the furnace to the south and to the north. The south run is pretty short, about 10'. The north run is longer... about 25'-30'. This long run supplies most of the heat to the house. Besides the vents that are located (almost) directly above this main heat duct there are 3 vents that are located about 25' away to the east. Each vent has it's own seperate supply duct work running to it. The three vents are located within 8' of each other in a straight line.

It looks like this....... ("+" is the furnace "-" and "l" are ducts)
(edit: I've added "o" to show nothing there. When I just used blank spaces the post looks good in message edit, but the format gets messed up when I submit the post.)
oooooooo ----------------------------
oooooooo l oooooo l o l o l oooo
----------+ ooooo l o l o l oooo
oooooooooooooooo l o l o l oooo
oooooooooooooooo l o l o l oooo
oooooooooooooooo l o l o l oooo

Ok? So I have about 75' of ductwork running East (25' x 3). Should I condense these into one line? Before I didn't have a problem because the ducts are exposed to the living area so the ducts are in fact heating that area as they heat and cool and leak. But with the drywall up I'll be trapping that heat and I'm going to loose it (at least loose it's effectiveness). However... I'll be adding a 90 degree bend to the line, so will that restrict the airflow to much?

New system would look like this...

oooooooo ----------------------------
oooooooo l oooooo l ooooooooooo
----------+ ooooo l ooooooooooo
oooooooooooooooo l ooooooooooo
oooooooooooooooo l ooooooooooo
oooooooooooooooo ------------ oooo


Sorry, I'm clueless here. I'm trying to go by common sense but I don't know if there is something I would be overlooking. Any comments on my ideas?

Thanks,
Micah
 

Last edited by mwolf1; 10-13-03 at 06:04 AM.
  #2  
Old 10-13-03, 12:29 AM
lynn comstock
Visiting Guest
Posts: n/a
I don't get the picture. Whatever you do, don't finish the basement until you are satisfied with the airflow from the revised ductwork.

Each turn can add friction equivalent to 30 to 100 feet of straight ductwork of the same size. In a basement the ducts are likely to have a high aspect ratio and thus have higher friction losses. SEE:
http://www.snipsmag.com/CDA/ArticleI...,64675,00.html
The best online information I've found so far is at:

http://www.llbuildingproducts.com/ll...ips-frame.html
 
  #3  
Old 10-13-03, 06:43 AM
mwolf1
Visiting Guest
Posts: n/a
I've edited the drawings above to clarify them. I had some formating problems that messed up my already rough drawing.

Thanks for the reply Lynn. I think that (how much friction a bend adds) is the information I was really looking for, just didn't know how to ask it.

The more I look at it the more I think I'm going to go ahead and attempt the changes. I plan on insulating the ceiling to help keep the noise in the basement it seems like removing those three ducts that run across the room would help a lot. I plan to do some more research on it first but as of now my planned layout would look like this:

oooooooo ----------------------------
oooooooo l oooooooooooooooooooo
----------+ ooooooooooooooooooo
oooooooo l oooooooooooooooooooo
oooooooo l oooooooooooooooooooo
oooooooo ---------------------- oooo

I now plan on coming right off the furnace and using the larger box style duct for the rerouting. In this way I won't be adding any extra 90 degree bends. With the larger ductwork I hope to reduce some of the friction. Some new questions I'll be looking to answer...

1. Is there a limit on the number of ducts you want coming straight off the furnace? If I go from 2 to 3 are there any negatives I can expect?

2. The new portion of duct work I will want to run as close to the basement exterior wall as possible. It will also be fully enclosed once the drywall goes up. I am concerned about moisture collecting between the warm enclosed ductwork and the cool wall. So...
2a. I plan to install a vapor barrior, sealing the duct joints, and adding insulation (R13-R18) around all sides of the ductwork and against the wall. (I got an awesome deal from my part time job at a home improvement store on some Owens Corning expanding fiberglass insulation.. half price) Anything else I can do? I planned on using metal ducts, but maybe plastic would conduct less heat? Thoughts... ideas...?
2b. I wonder if there are any codes for distance of ductwork from walls. I know codes vary locally so who do I contact to find out this information?

Thanks for any feedback I recieve. I'll check out those websites.

-Micah
 
  #4  
Old 10-13-03, 01:38 PM
lynn comstock
Visiting Guest
Posts: n/a
1. Is there a limit on the number of ducts you want coming straight off the furnace? If I go from 2 to 3 are there any negatives I can expect? No

2. The new portion of duct work I will want to run as close to the basement exterior wall as possible. It will also be fully enclosed once the drywall goes up. I am concerned about moisture collecting between the warm enclosed ductwork and the cool wall. So...
2a. I plan to install a vapor barrior, sealing the duct joints, and adding insulation (R13-R18) around all sides of the ductwork and against the wall. (I got an awesome deal from my part time job at a home improvement store on some Owens Corning expanding fiberglass insulation.. half price) Anything else I can do? I planned on using metal ducts, but maybe plastic would conduct less heat? Thoughts... ideas...?
Duct sealing AND sealing the vapor barrier as well should give you full protection.
2b. I wonder if there are any codes for distance of ductwork from walls. I know codes vary locally so who do I contact to find out this information? No need that I know of. The local building official (inspector) can tell you.
 
 

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