replacing heat only system to a/c

[speedytom]

ok iv been in the trade for about 3 years, i can install the systems no problem but i have yet to go to a duct sizing class so im not sure on trunk line sizes and duct sizes to each room. so can anybody point me in the right diection for info on sizing my duct system. if you have questions feel free to ask.

also one other thing. the house is poorly insulated, it is 1150 sq.ft. im planning on installing a 3.5ton 13seer system with a bump coil. is it smart for me to bump the system a half ton to compensate for poor home insulation?

thanks
tom

[RyanHughes]

Poorly insulated or not I think you're making a mistake by oversizing if you install a 3.5 ton with less than 1200 sqft. Around here that would be 2-2.5 ton max, even if insulation improvements could be made.

Since this is your home, I would spend the time to get some advice here (as you're doing) with the duct sizing and also run your own load calculation to determine how much capacity you need. You don't want an oversized system that's going to cost you more to purchase, operate and maintain.

[tinner73]

fill out your profile:rolleyes: then we can help you.

[marvin]

it would be smart to have a load calc. ran & then follow it.

[beenthere]

Hard to believeyou have more then around 18,000BTUs sensible load.

If you over size the way it sounds like yoour going to. You may end up with a BIG MOLD PROBLEM!

[speedytom]

Hard to believeyou have more then around 18,000BTUs sensible load.

If you over size the way it sounds like yoour going to. You may end up with a BIG MOLD PROBLEM!

will do about the profile. i did tell the cutomer about the mold problem becaus eof the oversizing. but like i said the house does have terrible insulation. guess i need to find a place to get a load calc done. thanks

[beenthere]

Use This (http://hvaccomputer.com/talkref.asp)

[ascj]

ok iv been in the trade for about 3 years, i can install the systems no problem but i have yet to go to a duct sizing class so im not sure on trunk line sizes and duct sizes to each room. so can anybody point me in the right diection for info on sizing my duct system. if you have questions feel free to ask.

also one other thing. the house is poorly insulated, it is 1150 sq.ft. im planning on installing a 3.5ton 13seer system with a bump coil. is it smart for me to bump the system a half ton to compensate for poor home insulation?

thanks
tom

Being the trade for only 3 years, I hope you work for a company. And if you do, there should be somebody that can perform a manual J on the house, then perform a manual d to size the ductwork. Also try to get involve with the design, so you can learn abit.

[beenthere]

I was figuring R9 insulation in the walls, and ceiling.

[speedytom]

yes i do work for a company but i dont believe we use any load calc programs. i have never seen or heard my boss talk about it. we usually do retro-fits really no new installations. we are a small company with me and two other techs.

edit: i do not know the type insulation, but i do know that it is old and mostly single oane windows amd pretty thin walls

[speedytom]

Use This (http://hvaccomputer.com/talkref.asp)

pretty cool ill download it and check it out thanks

[beenthere]

Use that software. And you'll be surprised how much heat a wall doesn't gain.

[ascj]

yes i do work for a company but i dont believe we use any load calc programs. i have never seen or heard my boss talk about it. we usually do retro-fits really no new installations. we are a small company with me and two other techs.

edit: i do not know the type insulation, but i do know that it is old and mostly single oane windows amd pretty thin walls

No offense, but retrofits require a load calc and ductwork design. You will be surprised on how many jobs you land by doing them.

Most don't do them, thank god our salesman were forced to do them awhile back, because of New Jersey rebates. Now they realize how it's gives them a competitive edge.

[speedytom]

No offense, but retrofits require a load calc and ductwork design. You will be surprised on how many jobs you land by doing them.

Most don't do them, thank god our salesman were forced to do them awhile back, because of New Jersey rebates. Now they realize how it's gives them a competitive edge.

i know it but im just a tech so i just do as im told ya know. but this job is for a family friend who just had a baby and im trying to figure out if i wanna do it or pass it off to the next guy. i know it is a huge job.

[ascj]

i know it but im just a tech so i just do as im told ya know. but this job is for a family friend who just had a baby and im trying to figure out if i wanna do it or pass it off to the next guy. i know it is a huge job.

It seems you really care about how the job turns out. If your not comfortable with it, then I would guess to say, leave it to someone who is. But at the same time being involved to make sure it is done right and the same time you will learn from it.

[beenthere]

ascj is just trying to get you to realize how easy it is to have an oversized A/C that still doesn't cool right. Or cost a fortune to use to cool a house.

Not uncommon to find a 2,000 sq ft house with a 4 ton A/C. And the customer ask for a 5 ton.
Then when you check out the system. you find the house only needs 3 tons at most.
And the current duct system for that 4 ton unit is only moving 1050CFM.

So many guys think .1"FR on a ductulator is .1" static pressure. That many systems have grossly undersized duct work. And run at .9" TESP, or more.

[speedytom]

ascj is just trying to get you to realize how easy it is to have an oversized A/C that still doesn't cool right. Or cost a fortune to use to cool a house.

Not uncommon to find a 2,000 sq ft house with a 4 ton A/C. And the customer ask for a 5 ton.
Then when you check out the system. you find the house only needs 3 tons at most.
And the current duct system for that 4 ton unit is only moving 1050CFM.

So many guys think .1"FR on a ductulator is .1" static pressure. That many systems have grossly undersized duct work. And run at .9" TESP, or more.

thats excatly what im worried about is the undersizing of duct work. i appreciate all the help.

[udarrell]

There are a lot of factors involved in designing duct systems.

It wouldn't hurt to look at an overview of some of the factors:
http://www.udarrell.com/proper_cfm_btuh_duct_sizing_air_conditioning_syste ms.html
It is not everything you need to know but it might help & is just a rough outline.
Or click my name above & use contact info.

[MADHVACTECH]

Here is a different link for equipment sizing http://www.energycodes.gov/rescheck/download.stm it has some usefull information on it.