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comdal
08-10-2004, 09:45 PM
I am remodeling a basement and would like to increase the ceiling height below the cold air and supply ducting. Can ductwork be purchased or made that is wider and more narrow (floor to ceiling) providing me with more headroom?

pricer
08-11-2004, 04:44 AM
It is possible. What size are the ducts? The new duct will have a ratio greater than one to one, height / width, the cost of the material will increase because the duct will require more material so the duct can retain the correct size for the design. If the duct were in your residence, I don't think it would be a huge issue due to the size of the duct. Depending on the severity of the height to width change and the layout of the duct itself, fittings will need to be made to reconnect the new, modified duct back to the existing duct. Your local contractor should be able to help you with this, it would be difficult for us to accurately give you all the answers that you will need for your project.

Give us some additional information and maybe we can help. If you have any more questions feel free to ask and welcome to the shop.

Gate
10-27-2004, 05:20 PM
I remember this topic posted in NNTP... alt.home.repair or alt.hvac can't remember which...
To decrease the height by 2 inches requires more than 2 inches increase in width to maintain proper airflow. Most residential ductwork is 8 inches high. to reduce it to 6 inches... can be alot of work and cost for a 2 inch gain. To divide it in two and change the height from 8 inches to 4 - is ridiculous. :roll:

peace,
-Gate

10-28-2004, 04:42 PM
Gate, Let me save you some heartache. If the duct was 12X12 the cubic inch is a 144, right. Just measure the duct you got right now (this on the premise that the installer got it right the first time?) and do your home work. If you know the size of your unit in tons or btus (12000 btus=1 ton) The thought here is 400 cubic feet minute per ton? The average manufacture actually runs it at about 600 cfm per ton. This covers their ass in the event of a clogged filter or lousy duct sizing. If you know all the other criteria, hereís a simple math formula which is the same as a ductulater slid rule which in your case will be just be fine. CFMX144 inch divided by 800 FPM (do not exceed 800 feet per minute if you donít want noise in your house) and this will give you your cubic inches. If you do not know the size of your unit, just post the model number of your condenser in the back yard or your furnace if you donít have A/C and I will tell you. Note: you will find your info sticker on the inside wall of your furnace. Hope to solve your problem. Bob Luland
Ps: Stop going to alt-hvac. Its bad for your brain!

Bud
10-29-2004, 04:30 AM
Gate, Let me save you some heartache. If the duct was 12X12 the cubic inch is a 144, right. Just measure the duct you got right now (this on the premise that the installer got it right the first time?) and do your home work. If you know the size of your unit in tons or btus (12000 btus=1 ton) The thought here is 400 cubic feet minute per ton? The average manufacture actually runs it at about 600 cfm per ton. This covers their ass in the event of a clogged filter or lousy duct sizing. If you know all the other criteria, hereís a simple math formula which is the same as a ductulater slid rule which in your case will be just be fine. CFMX144 inch divided by 800 FPM (do not exceed 800 feet per minute if you donít want noise in your house) and this will give you your cubic inches. If you do not know the size of your unit, just post the model number of your condenser in the back yard or your furnace if you donít have A/C and I will tell you. Note: you will find your info sticker on the inside wall of your furnace. Hope to solve your problem. Bob Luland
Ps: Stop going to alt-hvac. Its bad for your brain!

Here is a link to something I have started to put together on different designs of systems. I wouldn't mind a bit to grow this section of the site one bit if there is an interest to this. I myself would love to focus on this and other areas of system design.

Should we move forward on this? Input?

Air Flow and Design (http://www.thesheetmetalshop.com/pn/index.php?module=htmlpages&func=display&pid=178)

Bd_Blues
11-15-2004, 01:54 AM
I'm Thinking There Are Way To Many Variables In This Situation To Really Answer This Question. I Would Say You Need To Have A Contractor Look At It (Make It Two Or Three Contractors) In Existing Situations Such As These You May Do More Harm Than Good In The Long Run. I Mean How Bad Do You Need The Space Is Worth Losing Some Efficiency Or Worse Losing Some Life Expectancy Or Damage To Your Equipment.

If Cost Is An Issue; You May Be Able To Reroute The Duct Work, Saving You The Cost Of All New Duct. A Couple Of Fittings May Do The Trick But Then Again You Need To Keep Them And The Configuration Within Cretin Design Constraints. As The Gentlemen Above Stated Donít Make Your Duct To Small Or Constricting, A Few Inches Of Head Space Could Cause A Plethora Of Problems In The Long Run.

One Other Option Would Be To Incorporate The Duct Into Your Architectural Design, And Leave It Exposed. You Would Then Save Money On Ceiling Materials And Labor. Maybe Add That Plasma Screen T V You Were Looking At. To The Mix.


Heck Itís Residential Just Go To Home Depot And Flex It LOL


Great Site You All Have Here. Suprised I Had Not Found It Sooner!! Really Like The Airflow Page My Vote Is (masc. pl. nom) Let Those Who Have Eyes See!!!!!

Kind Regards,

Matt

pricer
11-16-2004, 07:17 PM
I'm Thinking There Are Way To Many Variables In This Situation To Really Answer This Question. I Would Say You Need To Have A Contractor Look At It (Make It Two Or Three Contractors) In Existing Situations Such As These You May Do More Harm Than Good In The Long Run. I Mean How Bad Do You Need The Space Is Worth Losing Some Efficiency Or Worse Losing Some Life Expectancy Or Damage To Your Equipment.

If Cost Is An Issue; You May Be Able To Reroute The Duct Work, Saving You The Cost Of All New Duct. A Couple Of Fittings May Do The Trick But Then Again You Need To Keep Them And The Configuration Within Cretin Design Constraints. As The Gentlemen Above Stated Donít Make Your Duct To Small Or Constricting, A Few Inches Of Head Space Could Cause A Plethora Of Problems In The Long Run.

One Other Option Would Be To Incorporate The Duct Into Your Architectural Design, And Leave It Exposed. You Would Then Save Money On Ceiling Materials And Labor. Maybe Add That Plasma Screen T V You Were Looking At. To The Mix.


Heck Itís Residential Just Go To Home Depot And Flex It LOL


Great Site You All Have Here. Suprised I Had Not Found It Sooner!! Really Like The Airflow Page My Vote Is (masc. pl. nom) Let Those Who Have Eyes See!!!!!

Kind Regards,

MattMatt,

I meant to say it earlier, I really like the quote you have placed with your signature. Wisdom, just can't beat it. Welcome to the "Shop" , we hope you come back and share more wisdom.

Thank You,

ken_halt
02-15-2005, 01:05 PM
would like to know duct sizes for 100.000 btu furnace 3 ton condenser cape cod house 2 story 5 rooms total 1500 sq ft how many btu,s/run etc i know room size makes a big diffrence any sites that can helpme calculate this

ken_halt
02-15-2005, 01:08 PM
would like to know duct sizes for 100.000 btu furnace 3 ton condenser cape cod house 2 story 5 rooms total 1500 sq ft how many btu,s/run etc i know room size makes a big diffrence any sites that can helpme calculate this

02-15-2005, 02:53 PM
Ken, Word to the wise. Hire your self a qualified contractor and you will be a much happier camper in the end. In your queastions I can hear that you are going to get in to some thing way over your head. Bob

Bud
02-15-2005, 05:40 PM
What do you mean "Duct Sizes," What you need to understand about airflow is simple, yet can be complicated. For the air to maintain the velocity at the end of the run, so it has any relevence left, you need to understand how air flows. NO ONE can righfully answer this question, to many variables? Each room has an heatloss or heat gain, this requires X amount of CFM, once the CFM is determined for each room now you can do something. But I would first think about a total heat loss on your home, it's hard for me to picture a 100,000 btu furnace in Florida?

CFM Ė (cubic feet per minute) this is the volume, or the quantity (amount) of airflow. In formulas you will see CFM expressed as Q or quantity.

FPM Ė (feet per minute) this is the velocity, the speed at which the air flows.

Static pressure (SP) - Velocity pressure (VP) - Total pressure (TP)

Static pressure is the pressure that works at pushing or exerting outwards; a good example is that of the balloon or inflatable raft, it is the static pressure that keeps these items inflated. As you increase the size of the balloon or raft by increasing the volume you in turn increase the static pressure, this increase in static pressure continues until you reach the burst point. In ductwork it is the static pressure that pushes on the inside trying to get out. Static pressure is used to overcome frictional and other resistances to air flow. Static pressure is what makes the air flow!

Velocity Pressure is the air thatís flowing; the air from your mouth to blow up the balloon or raft is a result of velocity pressure. This is important if you want air to come out of the register?

Total pressure is made up from the two components, velocity pressure and static pressure. By understanding this equation (TP = VP + SP) we know that static, velocity and total pressure are interrelated. This means velocity pressure can be converted to static pressure and static pressure can be converted to velocity pressure. Don't worry about this stuff yet:)

The idea is to have an evenly balanced system that will help maintain even tempertures across the home. There are a lot of peole that toss in ductwork and then complain the next many years, because "the registers don't work right" :) It has nothing to do with the air flow.

Let us know what you come up with on the heatloss. I'm courious?

pricer
02-15-2005, 06:18 PM
What do you mean "Duct Sizes," What you need to understand about airflow is simple, yet can be complicated. For the air to maintain the velocity at the end of the run, so it has any relevence left, you need to understand how air flows. NO ONE can righfully answer this question, to many variables? Each room has an heatloss or heat gain, this requires X amount of CFM, once the CFM is determined for each room now you can do something. But I would first think about a total heat loss on your home, it's hard for me to picture a 100,000 btu furnace in Florida?

CFM Ė (cubic feet per minute) this is the volume, or the quantity (amount) of airflow. In formulas you will see CFM expressed as Q or quantity.

FPM Ė (feet per minute) this is the velocity, the speed at which the air flows.

Static pressure (SP) - Velocity pressure (VP) - Total pressure (TP)

Static pressure is the pressure that works at pushing or exerting outwards; a good example is that of the balloon or inflatable raft, it is the static pressure that keeps these items inflated. As you increase the size of the balloon or raft by increasing the volume you in turn increase the static pressure, this increase in static pressure continues until you reach the burst point. In ductwork it is the static pressure that pushes on the inside trying to get out. Static pressure is used to overcome frictional and other resistances to air flow. Static pressure is what makes the air flow!

Velocity Pressure is the air thatís flowing; the air from your mouth to blow up the balloon or raft is a result of velocity pressure. This is important if you want air to come out of the register?

Total pressure is made up from the two components, velocity pressure and static pressure. By understanding this equation (TP = VP + SP) we know that static, velocity and total pressure are interrelated. This means velocity pressure can be converted to static pressure and static pressure can be converted to velocity pressure. Don't worry about this stuff yet:)

The idea is to have an evenly balanced system that will help maintain even tempertures across the home. There are a lot of peole that toss in ductwork and then complain the next many years, because "the registers don't work right" :) It has nothing to do with the air flow.

Let us know what you come up with on the heatloss. I'm courious?Well put.

bordontn
02-16-2005, 08:06 PM
Bud...A 3 Ton A/C rated at 1200 cfm/36000 btu's won't neccessarily deliver that if your total S.P. of your duct system/coil(wet),grilles,filter total more than your unit is capable of producing at that total s.p...At .08 s.p.per 100',That's .0008 per foot.A total of 250 ft. might exceed the design of your unit.At 10' per 90 degree ell,35' per round take off,filters
boots,length of runs,length of trunk,etc. it adds up fast....You could end up using a 4 ton furnace with a 3 ton coil..
bordontn

Bud
02-16-2005, 08:26 PM
I don't doubt the need for three tons (if this is what the final calcs call for) I questioned the 100,000 btu furnace for a 1500 sq.ft home. In this neck of the woods an average and I say average:) 1500 sq ft home would need about 80,000 btu at most. 100,000 in florida :) I understand they may need the drive for the A/C, but isn't there away to accomadate a smaller furnace with more drive, 80,00 btu furnace has 3 ton drives? What seer rating is the A/C system.
This is what I meant by to many variables:) What would happen if he chose a variable speed furnace / two stage, the high fire would not kick in until the demand was there?

02-17-2005, 04:24 PM
Bud, Youíre right, Couldnít help my self. Ran a load calculation on a hypothetical home of 1500 sq ft located in Jacksonville FL. I put windows all over it including two eight-foot picture single pane. Two doors. No insulation in walls or ceiling. Even gave it leaky construction standard and only came up with a load of 29,252 heating and 29,212 cooling. I think a heat pump with electric back up would do just fine. Bob

rdk1
06-22-2005, 03:48 PM
I would think there may be much more to it than that.. granted I'm not a metal expert.. but... a lot of the basic sizing depends simply on total feet (linear), and exactly where the air handler/furnace will be located in relationship to the other supply and return lines (drops). As far as decrease/increase in size to accom 'headroom" I'm not sure, but don't think its that simplistic either.. I would expect these sizings/shapes to have direct relationship to change the overall velocity of the air. Such as the difference between round vs "square" duct. .. wouldn't it ?? What I did to my basement duct ?.. I painted it...call it camoflage..actually, it looks pretty good...works for me.. Although at times I have to duck... or is that duct !!