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drewhart 01-26-2009 03:01 PM

determining duct size and placement
i am planning to install a furnace and duct work in a house that had radiant heat. where should i place the vents, renturn vents, and what size ducts should i use? the house is 1904 sq.ft, 2 story, 4 bedroom, cleveland ohio, new windows up, old down, insullation up, none down. full sized basement.

beenthere 01-26-2009 03:25 PM

Duct sizes are determined by how many CFM your house needs.
This can be found by doing a load calc.

Which is also how you determine what size furnace your house needs.

drewhart 01-26-2009 05:24 PM

doing a load calc sounds like alot of fun. i majored in physics, what is the formula for doing the calc?

beenthere 01-26-2009 05:42 PM

If you use this program, its easier, then doing all the long math.

hvaclover 01-26-2009 09:25 PM


Originally Posted by drewhart (Post 219627)
doing a load calc sounds like alot of fun. i majored in physics, what is the formula for doing the calc?

Aw jeeze....we got another Oppenheimer...

dac122 01-27-2009 07:47 AM

Step one is to size your furnace. Manual J is what will do that for you or HVAC-Calc. Manual D is what is needed in planning your duct work.

tk03 01-27-2009 08:59 AM

I don't understand why you would want to eliminate a radiant system for a forced air system unles the radiant system is not working. The comfort level between the two is very different. If you are doing this here is another site to check for more heat loss info and the importance of

drewhart 01-27-2009 06:17 PM

yes the radiant heat system was severly damaged. the entire system must have frooze in the past ( i recently bought the house) the boiler has a big hole in it, and lots of pipes in the walls have long slits in them. some of the radiators leak, and most of the flanges in the basement lines leak. and all this was found before the system was fully filled up (no pressure or heat).

i have spoken to many experts in the field, all of whom say not to put in a full forced air system. they all say to run pex tubing to basboard heaters, or, the idea i like best, install electric baseboard heat on the second floor, along with a small furnace for the first floor.

the quote i got to install a new boiler was 6,000. so i do not want to go the pex tube route.

drewhart 01-27-2009 06:21 PM

available static pressure calculation question
i am planning on installing a furnace to heat the first floor of a home. (second floor will be heated by electric base heat). i am installing a furnace only, no cooling. when calculating the availble static pressure, there will be no subtraction for a coil right? it seems the coil causes the largest pressure drop. the filter, registers and return grills cause a small drop in comparrison. does this mean that without cooling, the duct design will be smaller?

drewhart 01-27-2009 07:15 PM

i downloaded this program's free trial. i entered all the information for the house and it says "free trial" in the box about the total heat loss. i dont think they give the answer for free. does anyone want to help me out if i provide you with the numbers?;)

or rather, does anyone know where i can get manual J? i would like to do this calculation by hand. i read the manual on duct design at the library today, but they dont have manual J.

hvaclover 01-27-2009 07:46 PM

Buy one like we pros and HOs did.

Penny wise pound foolish

beenthere 01-27-2009 07:49 PM

Amazon may sell it.
You can also buy it from ACCA.

Check the furnace. Some furnaces want you to use a low ESP when its heat only.

Aggie67 01-27-2009 08:11 PM


Originally Posted by drewhart (Post 220340)
i dont think they give the answer for free. does anyone want to help me out if i provide you with the numbers?;)

When it comes to calculations from licensed professionals, very little is free. I doubt someone is going to give away a set of calcs for you, unless you know someone personally that can do them.

hvaclover 01-27-2009 09:03 PM

He ain't gettin' mines fo' free. MM MMM, BROTHER

drewhart 01-28-2009 10:04 AM

is it ok if i use electric baseboard heaters on the second floor to issolate the first floor as a one story house when doing this calc?

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