what size would you do.

[ironpit]

Got a call to install an evap. coil and a/c in a modular. Total square foot about 1300, 2 x 6 walls, minimal windows, new house. The factory installed a 4 ton blower in the a/h with 15 kw. There are a total of 6, count them SIX vents 2 1/4 by 12. Also r32 in attic. No adding new vents. Return is 20" flex.

[mgenius33]

Do a load calc, and advise whomever, what needs to be done to do the job properly. If they want it done otherwise, just make sure you get it in writing that they were advised.
Funny how some consumers can be so penny wise!

[HVAC_HUSKER]

load calc is the best way to go, the only way to ensure how many btu's are required sounds like a 4 ton is a little large to me. depending on heat load calc i would roll with a 3 ton with 10 kw. not sure the area your in but there is a formula to determine HS kw..

[ironpit]

Load cacl isn't going to help my pressures. Fairly mild winters around patoka lake. They are hard from time to time. We commonly use 2 1/2 or 3 ton for this type of home. Only they have more supplies.

The heat isn't my problem. The a/h came with the home.

I'm still dealing with a 4 ton blower and 6 supplies going on a 2 1/2 or 3 ton ac.

I was hired for a/c only.

[bunny]

There is no cookie-cutter answer when it comes to selecting equipment. Load calc....that's it.

Not meaning to sound critical, but......Is it just me, or is there a basic problem when a technician/business owner comes out here to ask fellow posters how to properly select equipment for a job?

This is certainly a good place to share ideas, experiences, etc. But if you're not capable of selecting/sizing/designing the proper equipment for a job and have to resort to assistance from an online group....might want to consider taking the necessary steps to ready yourself for this task.

[drife678]

Mobile home ductwork is awful.

[ironpit]

Thank you for the friendly advice. LOAD calcs DO NOT answer all questions.
LOAD CALCS are not cookie cutter annswers. You have to see the bigger picture. I don't have time to explain all of the details.

I think the guys have a handle on the scenario.

I have six vents for a 4 ton blower with 5 x 15 duct. We are going to have pressure problems as we are not allowed to increase circulation..

We are going to have a heat transfer problem.

Last time I checked load calcs had something to do with ductwork.

But that is just me. 4 tons is way too big to cool this house.

But I guess, really, I was just frustrated and wanted to share my feelings, with the guys. I really didn't want their advice. :whistle:

[drife678]

Surely the blower has multi speed selections. Call manufacture and find out what lower speed selections will do for your small duct.

[ironpit]

checked them. Thank you. The home owner is not open to new vents in her new floors.
No vents in three rooms, including the laundry ion the north end.

The factory should have done this right. This lady doesn't want the belly of her house cut open, to run new duct in a house that was supposed to be done right in the first place. The bathroom, dining room and laundry have no vents.

This is one of those I can't believe it jobs.

[gapfaff]

I'd be hesitant as well with out adding supplies and return. The way it stands I'd be at 1.5 tons with 2 ton evaporator and set fan to medium speed then see the pressures. Still not the best setup. I'd prefer a 2 ton with 4 more supplies. I think any larger with the good insulation you state would be too big.



Load cacl isn't going to help my pressures. Fairly mild winters around patoka lake. They are hard from time to time. We commonly use 2 1/2 or 3 ton for this type of home. Only they have more supplies.

The heat isn't my problem. The a/h came with the home.

I'm still dealing with a 4 ton blower and 6 supplies going on a 2 1/2 or 3 ton ac.

I was hired for a/c only.

[ironpit]

The really annoying thing is this house was sold by my accountant.He sells modulars.

He originally asked me if I was interested in the duct work and furnace part of the job, but I was swamped so I told him no. Plus the job is about 60 miles away.I told him he would save a lot of money and time to have the factory do it. They would do it right. The factory was unbelievably cheap. I couldn't touch their price.

[arc8]

Got a call to install an evap. coil and a/c in a modular. Total square foot about 1300, 2 x 6 walls, minimal windows, new house. The factory installed a 4 ton blower in the a/h with 15 kw. There are a total of 6, count them SIX vents 2 1/4 by 12. Also r32 in attic. No adding new vents. Return is 20" flex.

I would size it based on the Heat Load performed.



Load cacl isn't going to help my pressures. Fairly mild winters around patoka lake. They are hard from time to time. We commonly use 2 1/2 or 3 ton for this type of home. Only they have more supplies.

The heat isn't my problem. The a/h came with the home.

I'm still dealing with a 4 ton blower and 6 supplies going on a 2 1/2 or 3 ton ac.

I was hired for a/c only.


Without a load calc; how would you know what "pressures" you even need?



Thank you for the friendly advice. LOAD calcs DO NOT answer all questions.
LOAD CALCS are not cookie cutter annswers. You have to see the bigger picture. I don't have time to explain all of the details.

I think the guys have a handle on the scenario.

I have six vents for a 4 ton blower with 5 x 15 duct. We are going to have pressure problems as we are not allowed to increase circulation..

We are going to have a heat transfer problem. Last time I checked load calcs had something to do with ductwork.

But that is just me. 4 tons is way too big to cool this house.

But I guess, really, I was just frustrated and wanted to share my feelings, with the guys. I really didn't want their advice.


You can't produced an answer without seeing the whole "picture", via a Load Calc.




checked them. Thank you. The home owner is not open to new vents in her new floors.
No vents in three rooms, including the laundry ion the north end.

The factory should have done this right. This lady doesn't want the belly of her house cut open, to run new duct in a house that was supposed to be done right in the first place. The bathroom, dining room and laundry have no vents.

This is one of those I can't believe it jobs.


Produce a Heat Load Calc and show the customer. Doesn't the IMC require it? If you do it your way; you're just guessing. Any way you wouldn't have any proof of evidence why your installs would be right without a Qualified document (Load Calc)!

[ironpit]

I diidn't say I did not do a heat load calc, nor did I say it wasn't a proper thing to do.But at this point with a 4 ton blower on 5 x 15 duct with 6 vents I can see other problems.
For the record I did not do a load calc,as of yet. I will.

But I am stuck with this air handler and 6 vents. Is it just me or do I see problems?

I know the duct work is wrong. There are three rooms without vents and I've got a lady with a new house who isn't crazy about opening the belly of her house to install more ductwork on her new house.

Nobody is knocking a heatload calc.

I am trying to fit an a/c in a house that I know the ductwork is insufficient. I am trying to do it within the parameters I am given.

It isn't what I want to do, but I'm pretty much in the position of fitting the a/c to the duct instead of the duct to the a/c, as would normally be done with a load cal.

I'm stuck with the duct.

[jim147]

I'm stuck with the duct.

Then bid out what the duct will take and make the customer sign off on it or walk away.

Most times it's better to get out of a job instead of looking for a fix for something you know is not going to work.

jim

[ironpit]

THAT is exactly what I want to do! But this is my accountant and I do a lot of work for him.
Would hate to lose the account. Appreciate what you guys have said. I don't mean to minimize the load calc, I use Lennox calc sheets. But SO many times the existing ductwork in houses around here are way off.

You can't just throw the right sized equipment on the wrong size duct.
I sub for a couple of dealers and have worked for others.

The returns are sized from .1 to .05 . That is a huge difference.

Actually, it gets frustrating at times.I bust my butt to study, and it gripes me sometimes what I run across.
Thanks for your time.

[mgenius33]

What about using a lower rpm motor? Maybe an Evergreen, or something. Then pull one lead off a 5kw strip, and use turning vanes in the supply T.
If you're worried about the heat, use a two stg stat and set the differential high. Even at 15kw / 800 cfm it will only be about a 60* rise.

[gapfaff]

So, how old is this modular? shouldn't the manufacturer have some obligation to correct this? Warranty? Your Accountant has the pull to get this done as the selling dealer. I know the present owner doesn't want the floors cut for additional vents but they could be swayed to see the long term benefits? Is it on a crawl space? It could be done and insulation sealed back up properly but, labor intensive which is why the manufacturer should bare some financial responsibility.

[ironpit]

Brand new home. They just set it. Has a crawl. It's about sixty miles from here... and anywhere else. wet crawl and cut gravel. I notice that the duct under the furnace extends about a foot and a half past the furnace closet. There is no way to install the line set and condensate line without going thru the ductwork. It is impossible. I have no idea why they ran the duct like that. It serves no purpose that I can see.

I think I am going to walk away from this one.

Not familiar with Evergreen.

[gapfaff]

then the answer is simple...it's the manufacturers responsibility to make it right. Can't be done to code not having supplies in 3 rooms? In Wisconsin these modulars are inspected before and occupancy permit is given and that would not pass up here. Modulars are different than mobile home standards up here. Don't know about codes where you are located.



Brand new home. They just set it. Has a crawl. It's about sixty miles from here... and anywhere else. wet crawl and cut gravel. I notice that the duct under the furnace extends about a foot and a half past the furnace closet. There is no way to install the line set and condensate line without going thru the ductwork. It is impossible. I have no idea why they ran the duct like that. It serves no purpose that I can see.

I think I am going to walk away from this one.

Not familiar with Evergreen.

[gapfaff]

Don't blame you! homeowners should probably get a lawyer if the manufacturer doesn't agree to fix it. Sounds like they just threw in an airhandler they had in stock and didn't worry about sizing it properly. I have a similar horror story about a mfr venting a 92% TRANE furnace in a mod home. they used any pvc fittings they had lying around...tees in place of elbows etc. I was the TRANE tech they had to pay to correct the problem. So, if this mfr is reputable they'll get this resolved to the homeowners satisfaction. good luck.

[southshorejohn]

Then bid out what the duct will take and make the customer sign off on it or walk away.

Most times it's better to get out of a job instead of looking for a fix for something you know is not going to work.
jim
Ditto, been there, done that down the road when it doesn't work right guess who's fault it will be no mater what, :.02:

[ironpit]

Thanks guys. If you get the time, you should google indiana's hvac license requirements.

It's not like I don't know how to do a job from scratch in a professional manner, it's crap like this that frustrates me. Load calcs are obviously the right way to do a job, but they mean little of nothing if the ductwork is wrong.

There is a business in b'town that had a 5 ton a/c package unit installed 7 years ago. It has one 16 x 8 duict ran to the building. I have replaced two 1 hrse blower motors in the last couple of years. Now the compressor is acting up. I have told these guys repeatedly, duct work is killing you. Finally, they are going to change the ductwork.

[stopro1]

What you have is an oversized return and undersized supply for the 2.5-3T system you think is needed. With the oversized blower, and total static of the combined supply/return/registers there, you may end up with the 1000-1200 cfm you need. I would think that your 1600 nominal cfm blower, with as high as .8"-.9" of total esp imposed, could deliver a net cfm in the acceptable size range. Check the blower curve of the ahu. As far as your six supply registers go, assuming they are fed with 6" runouts.....they could deliver as much as 200cfm a piece with that kind of pressure built in the supply duct system. Noisy, yes....impossible, no.

With this type of home, minimal supply duct size is a necessity. It may be the very reason the return and blower were oversized.

[beenthere]

She'll change her tune about more supplies come winter when those rooms get cold.

[ironpit]

Stoppro1 You might be right. But that laundry room is gonna freeze. Thanks for the info.

[carmon]

install more supply vents or walk away... home owner will get over a few registers.... if not let them sweat

[ironpit]

Thank you carmon. I'm done with it. I'm walking away. The distance is too far for the trouble. And I can't stand the turkey farm next door. There are millions of flies around there. Thanks again.

[BURL-REF]

2 ton system