Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 12-18-2008, 12:20 PM   #1
Member
 
Join Date: Dec 2007
Posts: 149
Share |
Default

Duct help


I have a 3 ton zoned Trane unit (in the attic) and running flex ducts after the dampers out of the unit. Single story house in Ca. No runs over 25ft.

I'm running (2) 12" ducts and (2) 9" ducts out of the plenum.

(1) 12" will supply (2) 7" and (1) 5" registers
(1) 12" will supply (3) 7" registers
(1) 9" will supply (2) 7" registers
(1) 9" will supply (1) 7" and (2) 5" registers

I have (1) 16" (25x30" return in hallway), (1) 10" (from the zoned rooms) and (1) 6" fresh air intake from out side supplying the inlet side of the unit.

I also have a 12" manual pressure relief damper from the outlet plenum to the intake plenum, for the zoning dump off.

Does this all seem to be a good start on duct sizing? I'm looking to try and head off problem before I get to far in. Any suggestions or comments that might help me get in the right direction?

Thanks JIM

integlikewhoa is offline   Reply With Quote
Old 12-18-2008, 03:13 PM   #2
Member
 
Join Date: Sep 2008
Location: Portland, OR
Posts: 1,186
Default

Duct help


Need more information.

CFM of the furnace, cu ft of the house, cu ft of each room you intend to condition (or sq ft of each room and mean ceiling height), windows, insulation and type of weather you have year round.

At first glance the main ducts are oversized for the boot sizes.

__________________
My idea of a perfect day: No where to go and all day to get there.
Marvin Gardens is offline   Reply With Quote
Old 12-18-2008, 05:43 PM   #3
Member
 
Join Date: Dec 2007
Posts: 149
Default

Duct help


Quote:
Originally Posted by Marvin Gardens View Post
Need more information.

CFM of the furnace, cu ft of the house, cu ft of each room you intend to condition (or sq ft of each room and mean ceiling height), windows, insulation and type of weather you have year round.

At first glance the main ducts are oversized for the boot sizes.
Thanks for the reply.

The furnace is a 95% 2 stage variable speed system with 1400cfm blower (correction below).
The compressor is a 2 stage single compressor as well.

The house is a 3 bedroom 2 bathroom 1600 square feet home with normal 8ft ceilings. No vaulted ceilings anywhere. House has old wood windows and plaster walls from the 50's. Poor or no insulation threwout the house for now. I have the master bedroom gutted and found insulation in only 2 of the 4 walls and 3 are outside walls. I'm remodeling the whole house tho and will be updating everything. Master bath and bedroom are already started will be completed soon.

The bedrooms are only around 150sf each. 3 of them. The bathrooms are small 50-75 square feet. I have 4 zones setup. One in each room and one for the living, family, dining, main bathroom and kitchen.
The master bedroom has one zone which has a walk in closet and a bathroom. 5" register in the bathroom, closet and a 7" in the bedroom those are all on (1) 9" zone.

So for the takeoff coilers I have
(2) 12" for the main house zone (5) 7" registers and (1) 5" in the hall bath.
(1) 9" split to (2) 7" for the 2 bedrooms
(1) 9" to the rear master bedroom, bathroom and walk in closet.

The weather. I'm in Los Angeles Cali. I have 70's-80's most of the year, I have mid to high 40's right now and in the summer 100 or so for 2 maybe 3 months.

Correction on the CFM: I just checked the manual at
http://www.trane.com/webcache/un/furnaces%20(furn)/product/22-1814-02_01012008.pdf

It shows max flow at 1400cfm on stage 2 high heat with .5 external static pressure. 1360cfm at .1 and .7 external static pressure.

A/C shows 1200cfm max on my current settings.

Last edited by integlikewhoa; 12-18-2008 at 06:09 PM.
integlikewhoa is offline   Reply With Quote
Old 12-18-2008, 07:29 PM   #4
Member
 
Join Date: Dec 2007
Posts: 149
Default

Duct help


Anyone have any thoughts?
integlikewhoa is offline   Reply With Quote
Old 12-18-2008, 07:37 PM   #5
Member
 
Join Date: Sep 2008
Location: Portland, OR
Posts: 1,186
Default

Duct help


Okay, good information.

Looks to me that you will be mostly concerned about cooling in the LA area. Heating won't take much most of the time.

Each 12 inch duct will do about 900 cfm, each 9 inch will do about 400 cfm each. So total you have 2600 cfm in a 1400 cfm furnace. It will work but the air will be moving real slow till it hits the registers. Then it will pick up some serious speed.

The registers will take up all 1400 cfms till the air tries to get through the vents and then it will lose about 30% of the opening. This will increase the speed through the registers. Now there is a lot of debate on this on this forum. I like velocity as long as it isn't real fast so as to be drafty. Hvaclover has similar pregerences. Beenthere likes less flow because of the breeze.

The reason I like velocity is because I want the air to flow to the other side of the room and mix it up with the existing air.

This brings up another point. Location of the vents. I like vents up high on the wall or in the ceiling. This way there is nothing blocking the flow. If the vents are low on the wall or on the floor then you lose places on where you can put furniture. Can't have anything blocking the registers or you will have part of the room hot and the other cold. If they are in the ceiling or high on the wall then you have nothing blocking the flow.

If you choose to go with wall vents then you will have to get wall stacks. My guess is that you have 2x4 walls with 16 inch centers. This will handle a 3 1/2x14 wall stack. These work well with a 7 inch pipe or an 8 inch flex.

One wall stack will work nicely in a 150 sq ft room with an average number of windows, insualtion, and facing east or west. If the room faces south and gets a lof of sun then you would need a second wall stack.

Non insulated rooms, rooms with a lot of south facing windows, will need a lot more ventilation. The absolute worse room to ventilate is a kitchen that is south facing, uninsulated, lots of non thermal windows and no shade. I did one of these and even though it was a small kitchen I had to put in 4 stacks to get enough air to make it comfortable. I got called back about 4 years later since they had replaced the windows, insulated the walls and planted some diciduous trees for summer shade. Now the room was too cold and I had to retire two of the vents.

I almost always put extra vents in a kitchen since there are lots of heat producing appliances. I try for at least 2 wall stacks for the average kitchen.

An average bathroom can take a 6 inch, a small bathroom can take a 5 inch. Most average bathrooms will do fine with one well placed wall stack and a 7 inch pipe or 8 inch flex.

In larger rooms having 2 smaller wall stacks is better than having one big stack. It will get the air moved around better. Even if the stacks are on the same wall but 10 feet apart is better than one large stack.

You will need about 550 sq in for a return. One 30x18 would work and you can split this up as needed to smaller returns if you want more air movement in difficult rooms.

I suggest a small register in any walk in closet. Doesn't have to be big but air movement in a large closet is not a bad thing. A 4-5 inch would be fine in most cases.

Flex needs to be bigger because of non laminate flow compared to pipe which had much better laminar flow and therefore less friction loss.

Hope this helps. It is difficult to design an HVAC system long distance.

I must say that I did one for a doctor friend. He sent me the plans and I designed the system. Never saw the house but he called me the other day when it was -10 and was nice and comfortable. Made me feel pretty good.
__________________
My idea of a perfect day: No where to go and all day to get there.
Marvin Gardens is offline   Reply With Quote
Old 12-18-2008, 07:52 PM   #6
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,557
Default

Duct help


You still didn't say what size furnace it is, or what size 16i A/C it is.

Not gonna get 900CFM through 12" flex without going into a high static, which causes an ECM blower to use more electric then a standard PSC blower.

What zone panal are you going to use.
beenthere is online now   Reply With Quote
Old 12-18-2008, 08:18 PM   #7
Member
 
Join Date: Dec 2007
Posts: 149
Default

Duct help


Quote:
Originally Posted by beenthere View Post
You still didn't say what size furnace it is, or what size 16i A/C it is.

Not gonna get 900CFM through 12" flex without going into a high static, which causes an ECM blower to use more electric then a standard PSC blower.

What zone panal are you going to use.
It's a 80,000 btu part number TUH2B080A9V3VA

First sentence on the first post I have 3 ton unit. Heres the part number. 4TTX6036B1

The panel I have is a W8835 part number W8835A1004

The heater, panel, 3 thermostates (minus the room under contrustion), temp sensor out side, is all hooked up and working. I have the unit running currently, but dont have the duct work finished. The rooms all have thier register boxs installed (once again minus the room under construction) The plenum's are both installed with most of the starter rings on the outlet done and the intake all finished and run to the hallway and outside. Just need to run them to the return grills in all three rooms.
I dont have the outside a/c compressor hooked up, but the wiring and breakout box is there and the pad is there, just need to run the lines, hook the wires to the unit and charge it up.

In the attic I need to run all the ducts from the plenum to the already installed register boxs. Just planning runs and double checking everything before I compleye finish while there is some room for turning back.


integlikewhoa is offline   Reply With Quote
Old 12-18-2008, 08:25 PM   #8
Member
 
Join Date: Dec 2007
Posts: 149
Default

Duct help


All my vents and returns are on the celiing. I faced almost all my vents on celing 6" from the interior wall facing out toward the outside wall. Thats all done. In the bed rooms I aslo put the same sized returns on the opposite side of the celing, so on the other side of the room to incourage good air flow from one side of the room to the other.

All the 7" registers are 14x8" with 7" duct. Same goes for the Returns in the 3 bedrooms.
integlikewhoa is offline   Reply With Quote
Old 12-18-2008, 09:11 PM   #9
Member
 
Join Date: Sep 2008
Location: Portland, OR
Posts: 1,186
Default

Duct help


Quote:
Originally Posted by integlikewhoa View Post
All my vents and returns are on the celiing. I faced almost all my vents on celing 6" from the interior wall facing out toward the outside wall. Thats all done. In the bed rooms I aslo put the same sized returns on the opposite side of the celing, so on the other side of the room to incourage good air flow from one side of the room to the other.

All the 7" registers are 14x8" with 7" duct. Same goes for the Returns in the 3 bedrooms.
Overall it sounds like you have most of it covered.
__________________
My idea of a perfect day: No where to go and all day to get there.
Marvin Gardens is offline   Reply With Quote
Old 12-18-2008, 11:35 PM   #10
Member
 
Join Date: Dec 2007
Posts: 149
Default

Duct help


Quote:
Originally Posted by Marvin Gardens View Post
Overall it sounds like you have most of it covered.
Thanks, I was just making sure the number of vents, returns and the size of ducts I was going to use were correct.

The other thing im woundering is if I should put any manual dampers inline with the ducts anywhere incase I need to make some flow adjustments. Is this common practice or only if I run into a problem? Would this be something to install up stream right after each split or all the way down stream right before each register?

Thanks JIM
integlikewhoa is offline   Reply With Quote
Old 12-19-2008, 12:14 AM   #11
Member
 
Join Date: Sep 2008
Location: Portland, OR
Posts: 1,186
Default

Duct help


Quote:
Originally Posted by integlikewhoa View Post
Thanks, I was just making sure the number of vents, returns and the size of ducts I was going to use were correct.

The other thing im woundering is if I should put any manual dampers inline with the ducts anywhere incase I need to make some flow adjustments. Is this common practice or only if I run into a problem? Would this be something to install up stream right after each split or all the way down stream right before each register?

Thanks JIM
There are ways to restrict flow. Either inline dampers or you can use dampers in the registers.

I like having dampers that are reachable so that I can make slight adjustments in each room.

Since you are going to have 4 zones I don't think that you would need any dampers.
__________________
My idea of a perfect day: No where to go and all day to get there.
Marvin Gardens is offline   Reply With Quote
Old 12-19-2008, 03:21 AM   #12
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,557
Default

Duct help


The W8835 communitcating zone panel, is automatic mastering.

You gonna want manual dampers in your supplies, sine the largest zone is not automatically the master zone.

Zone 1 is always the main(programing zone) but not always the master zone.

Since a smaller zone can become the master zone.
If you don't have balanced air flow in a large zone of multiple rooms. A room could become too cool or too hot waiting for the master zone to bring on the heating or cooling.

Unlike most other resi zone systems. The W8835 slaves the zones.
Only calling for the furnace or A/C to run if the master zone requires heating or cooling.
beenthere is online now   Reply With Quote
Old 12-19-2008, 12:22 PM   #13
Member
 
Join Date: Dec 2007
Posts: 149
Default

Duct help


Well the ARD dampers I have can be adjusted on both how far they open and how far they close, and since each of the 3 room's will have one of those I figured I'm covered there (unless you suggest I put a manual anyways) only the living room, kitchen, dinning and family room I planned on possibly putting an inline manual damper, they are like 10-12 bucks each. I can add one right on top of each register, if need be. I could also add one right after the wye's where the ducts reduce to 7".
integlikewhoa is offline   Reply With Quote
Old 12-19-2008, 12:28 PM   #14
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 24,557
Default

Duct help


I would put one in each individual supply run.

Inline manual dampers are like a buck or 2 a piece.

If someone is charging you 10 to 12 bucks, look for another source.

The manual dampers aren't to control how much air a zone with multiple rooms on it has flowing to it. But to control how much air each individual room gets.
beenthere is online now   Reply With Quote
Old 12-19-2008, 01:09 PM   #15
Member
 
Join Date: Dec 2007
Posts: 149
Default

Duct help


Quote:
Originally Posted by beenthere View Post
I would put one in each individual supply run.

Inline manual dampers are like a buck or 2 a piece.

If someone is charging you 10 to 12 bucks, look for another source.

The manual dampers aren't to control how much air a zone with multiple rooms on it has flowing to it. But to control how much air each individual room gets.
The flat doors only are a few bucks. The ones I'm talking about are a 1 foot section of metal duct and the door in it. I know they sell the round door with the 2 pegs out both ends for cheaper. Plus I'm no HVAC contractor, so I'm sure I don't get the best prices. Does that sound right? Does it matter where they go? Upstream or down stream?

I'm thinking something like this attached to each register.
http://americanhvacparts.com/Merchan...e=duct-dampers

integlikewhoa is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Furnace install in attic - Duct configuration hartkem HVAC 6 11-08-2008 05:46 PM
Flex Duct Advice ssporty21228 HVAC 4 07-23-2008 08:28 PM
Condensation in Wall: Can I Seal a Dryer Duct With Caulk? xquercus HVAC 5 07-01-2007 02:33 PM
Modifying existing duct work Thurgee HVAC 3 04-05-2007 09:35 AM
1000-1400cfm...duct sizing Swordfish215 HVAC 1 01-15-2007 03:22 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.