Importance of "Manual J/Load Calc" when choosing an installer question

[southeflorida]

BACKROUND:We have a 2 zone system-2.5 ton each unit, for a total of 5 ton in a 2526 sqft single story, wood frame/ceder shake roof home that has LOTS of LARGE windows. One unit was replaced 5 years ago by previous owners. It's a 10 seer Trane, and does NOT have a varible speed handler. Both units cycle on and off about 8 times an hour during hot/humid weather (85+ degrees)and do not remove humidity as much as we would like or that we notice at our friends homes.
We are currently replacing the other (27 year old) unit this year, that is original to the house and still works.

Have had 2 estimates from dealers who are "Trane Comfort Specialists" listed on the Trane site, also members of the BBB with good records. I told both of our concerns re humidity and how the units cycle on/off so frequently (which I understand means the units could be sized incorrectly). I specifically asked about having a "Manual J" done...one just gave me "It's not nessecary" and the other said "It was done when the house was built and the system installed so you don't need one done now". (Note that the house was built in 1979). He also offhandedly added "if you really want one done we will do it for $130."

My Question: I've read that a 'load calc' should be done...Sould we INSIST on it? And should we have to pay for it?

[jrbenny]

Yes, it should be done -- especially a house that old. There's no telling what changes have been made since the original construction.

How they charge for it is up to them. Most folks just roll it into the cost of doing business. It's put in the equipment markup and/or labor costs. Some will do an adder.

I would look for someone that does a load calc and duct design as standard business, but that's just my opinion.

BTW...I fixed your title as requested.

[NormChris]

Yes, a load calculation should be performed before the system is selected. In fact, a load calculation is not only necessary to determine the correct system size, it is also used to determine the duct sizes. A room by room calculation is used to determine the branch duct sizes and the block load (whole house) calculation determines both the system size and the main duct run size.

As far as the load calculation having been accomplished when the home was built, did the contractor have a copy? Of course not. In addition, many things may have changed since the home was constructed which would change the heating and cooling loads.

Read the following article.

http://hvac-talk.com/vbb/showthread.php?threadid=33866

[leapfrog]

Originally posted by southeflorida
...one just gave me "It's not nessecary" and the other said "It was done when the house was built and the system installed so you don't need one done now". (Note that the house was built in 1979).It is necessary. The original builder may have oversized (or undersized) the system.

"a study in Florida of over 400 homes found more than 50% oversized the cooling equipment more than 120% of Manual J (James, et. al., 1997)"

http://www.fsec.ucf.edu/bldg/pubs/ACsize/index.htm

also:
http://www.nrel.gov/docs/fy02osti/31318.pdf

[southeflorida]

Thank you for your replies. You confirmed what I believed to be true and will be contacting other contractors who do load calcs as part of thier estimate process. Perhaps I am wrong but from what the research I've done recently it seems to be that both our units are incorrectly sized...due to the frequent cycling and that it is still fairly humid in the house. Agree?

I did read through the links provided...interesting and educational reading. Maybe I should print some off and supply them to the salesmen that were here? No....I'm sure they are well aware, but just...what? What were they thinking??

As to paying for a Manual J...we would pay for it, whether up front or added into the estimate.

Again, thanks for the replies. I have more Q's and hope you'll respond to my upcoming posts.

ps: jrbenny, thanks for fixing my title

[leapfrog]

No problem. I agree that it sounds like your systems are oversized.

Not everyone on the board will agree with me, but I've found that there are two behaviors which distinguish the really competent salesmen / saleswomen and installers from the rest.

The good sales folks ALWAYS offer to do a load calculation, and the good installers ALWAYS flow nitrogen when brazing linesets.

[fl1]

Originally posted by southeflorida
Thank you for your replies. You confirmed what I believed to be true and will be contacting other contractors who do load calcs as part of thier estimate process. Perhaps I am wrong but from what the research I've done recently it seems to be that both our units are incorrectly sized...due to the frequent cycling and that it is still fairly humid in the house. Agree?

I did read through the links provided...interesting and educational reading. Maybe I should print some off and supply them to the salesmen that were here? No....I'm sure they are well aware, but just...what? What were they thinking??

As to paying for a Manual J...we would pay for it, whether up front or added into the estimate.

Again, thanks for the replies. I have more Q's and hope you'll respond to my upcoming posts.

ps: jrbenny, thanks for fixing my title



They aren't "well aware",for the most part,the believe,there own story,rules of thumb,etc.,add most couldn't do a Manual J ,S or D ,correctly if their life depended on it.

Don't be surprised if you have 2 or 3 do the a Man. J,or say they did,that you get at least two different answers as to the correct size.

It's also very busy in your area now,and most all customers are more then willing to buy ,without the load calculation.

In fact many homeowners will insist on the same size as the old one,even when the calculation is done,and it's too large.Hard to believe but it's true!

[leapfrog]

If you want to be sure the load calc is done right you can always do one yourself.

Click on the HVAC-CALC link on the top of the page. The software costs $49 for home use - insignificant compared to the cost of a new system.

[southeflorida]

Leapfrog said:
"The good sales folks ALWAYS offer to do a load calculation, and the good installers ALWAYS flow nitrogen when brazing linesets."

So I should confirm the installers will "flow nitrogen when brazing linesets" when I have estimates done? (I don't know what that means and would appreciate if you'd educate me)

fl1 said:
"...most couldn't do a Manual J ,S or D ,correctly if their life depended on it.

Don't be surprised if you have 2 or 3 do the a Man. J,or say they did,that you get at least two different answers as to the correct size."

I will ask for a copy of the Manual J(s), but what to do if I get varying answers to size requirements?

fl1 said:
"It's also very busy in your area now,and most all customers are more then willing to buy ,without the load calculation."

I can believe that, easily....A) it's hot and humid now here, and will be for the next number of months. Heck, the consumer just wants to be able to sleep in comfort. B) I think too many consumers don't do much, if any, research and hence don't know what a "Manual J" is to begin with. I also suspect the salesmen who have been here believe these things too. I also suspect (and please correct me if I'm wrong) that A)if we were purchasing in Jan or Feb that we'd likly get a Man J done no problem as soon as I mentioned the cycling/humidity issues we have. B) the estimates on the cost of the new system would be less, perhaps by quite a bit.(we had planned on replacing the system during the winter. But new job related travel nixed that. I feel we HAVE to replace this old system now, in peak season, because we will be away too much of the time and if it were to fail while were were away for weeks we could come home to a nasty mold problem)