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Before there were computers there was a calculation sheet of paper. They might have even been a little faster as you didn't have re enter into a computer. You really don't need software for loads but the print outs are impressive and maybe less math errors.
Compare the sales benefit of a load calc compared to the contractor that scribbles a number on a piece of paper.
About 1979 I was working for a contractor and building a house after hours. They were breaking in a sales guy and he did a load off my plans and I got this impressive load calc along with a bunch of other stuff all nicely printed out. I knew the world had changed.
Maybe why a lot of contractors don't want to do calcs is if they only get 25-30% of their bids it seems like a waste of time.
On a commercial building there is little choice but to do the calc.

The firt thing you need ot understand is doing a load calc and doing one right are 2 different things. Around here half of the dealers do load calcs but most of those don't take the time to check insulation values, actually measure opening sizes, etc. Here is a good example of why load calcs need to be done. I did a new house, 2700 sq ft ranch, full basement with a walk-out to the north on the long side of the house, 3 ton, system has been in over 8 yrs with no problems. Other side of the coin, 800 sq ft house, full basement, leaky windows, 3 ton, not enough room in the house for 3 ton worth of air, squezed in 2.5 ton, system is short when it gets over 95*. That's why you do load calcs!!!!

I used to live in Dallas and know the relative humidity is much lower there than here on the SC coast. If we oversize a system here, the first summer will see us replacing the system because of a major mold problem. A half ton over is usually not a problem but any greater difference than that is begging for a problem.
And with the new "sealed foam envelope" homes these "green" contractors are building, it is VERY easy to oversize.

Originally Posted by hidalgo1301

I am in the process of convincing the company I work for the value of using load calculations and having software to assist in this process. I was discussing this with a tech today, and he began telling me this is all going to be a waste of time. "No one uses this stuff anymore, and I can tell you the cfm for a room just by looking." So..he got me wondering is it worth taking the time to learn to do proper load calculations? Does everyone here actually perform these calculations, or just feel they are important? He made the case that the time spent to perform a load calc. would not have good return was just not worth the time....

If a proper Manual J heat load calculation is performed, it can save your butt in a lawsuit.

That idiot tech friend of yours is a hack. You can tell 'im I said so.

Originally Posted by jimj

Go here http://www.acca.org/store/category.php?cid=2

Buy Bob's house for a couple of bucks, read it and then give it to your boss.
Maybe he will then buy Manual J, D, S and RS. Guess what your on your way to a never ending education. Congrats.

Thanks, I'll check it out. Oh, these guys don't seem to think subcooling, superheat, static pressure reading are worth checking on a regular basis..I'm out for the night fellas, thanks for the input and keepin my head up.

Originally Posted by hidalgo1301

I have not done a sizing of a new remodel, only of existing equipment. I have worked my way from installation to service, and have had more questions than answers on airflow and sizing equipment. It is pretty much the rule of thumb world around here. I don't have the experience, nor feel it proper to give a rule of thumb answer when sitting down with a homeowner on an estimate. I have really pushed after this summer giving estimates against other companies and not having the knowledge to give proper answers to questions. I can be very convincing, and could just "sell", but I feel that a homeowner is trusting me to do my best and give them professional technically sound advice. So..like I said I guess I will have to keep pushing. I really enjoy the company and people I work for and with, and believe that they want to give the best product possible. I just want to try to improve the process.

Go here http://www.acca.org/store/category.php?cid=2

Buy Bob's house for a couple of bucks, read it and then give it to your boss.
Maybe he will then buy Manual J, D, S and RS. Guess what your on your way to a never ending education. Congrats.

I have not done a sizing of a new remodel, only of existing equipment. I have worked my way from installation to service, and have had more questions than answers on airflow and sizing equipment. It is pretty much the rule of thumb world around here. I don't have the experience, nor feel it proper to give a rule of thumb answer when sitting down with a homeowner on an estimate. I have really pushed after this summer giving estimates against other companies and not having the knowledge to give proper answers to questions. I can be very convincing, and could just "sell", but I feel that a homeowner is trusting me to do my best and give them professional technically sound advice. So..like I said I guess I will have to keep pushing. I really enjoy the company and people I work for and with, and believe that they want to give the best product possible. I just want to try to improve the process.

Originally Posted by beenthere

Guess he thinks he can tell how much air is coming out of the register by feeling with his hand also.

Your rite, get the manual J out of the way and that pesky manual D gets in the way.

Guess he thinks he can tell how much air is coming out of the register by feeling with his hand also.

Originally Posted by hidalgo1301

We do residential replacement and remodels.

So how do you presently size your systems?

Originally Posted by hidalgo1301

Do you use it? Has it been beneficial to you? I ask just because I want the knowledge as well as to be able to be a benefit to the company that is willing to purchase this software.

It gives peace of mind and helps produce happy customers...a winning combination.

We do residential replacement and remodels.

If all you're doing is cookie-cutter structures, you may only need one calc adjusted for compass direction, but if you're doing any custom work...

Yes, I have one. It's older, put out by a manufacturer 10 years ago, simple to use and I like it. It came on a 3.5" floppy and I transferred the program onto my external hard drive before I gave up the floppy drive and now can put it anywhere I need it. Even an older one is better than none.

Originally Posted by air2spare

I know for a fact that 9 out of 10 contractors around these parts don't even have load calculating software much less how to use it

Do you use it? Has it been beneficial to you? I ask just because I want the knowledge as well as to be able to be a benefit to the company that is willing to purchase this software.

Originally Posted by air2spare

I know for a fact that 9 out of 10 contractors around these parts don't even have load calculating software much less how to use it

So if your one that does that puts you in the top 10%. Good place to start the sales process.

It is common for mechanical systems in residential construction to be oversized which increases installation costs, wastes energy, and reduces comfort and moisture control. Properly sized equipment will last longer, provide greater comfort, reduce noise, and save homeowners money. Yet both builders and code officials are uncertain how to evaluate such calculations to assure they meet the intent of the code plus the sizing methodology approved in Air Conditioning Contractors of America (ACCA) Manual J (or equivalent).

The 2003 IECC requires sizing calculations to be performed on every home using the procedures described in the ASHAE Fundamentals Handbook - 2001. Chapter 14 of the 2003 IRC requires heating and cooling systems to be sized to ACCA Manual J - Seventh Addition or other approved heating and cooling load calculations. Both methods have sufficient built-in safety factors to accommodate most conditioning needs. Therefore, it is important to follow all instructions in ASHRAE Fundamentals or Manual J using precise area measurements and specific data.


Heating and cooling loads can be determined using a whole house approach or performing a room-by-room load calculation. The room-by-room approach provides the information needed to determine the number of cubic feet per minute (cfm) needed of conditioned air to satisfy the heating and cooling load for the room. This information can then be use to determine the duct size necessary to deliver space heating and cooling for the space.

http://resourcecenter.pnl.gov/cocoon...r/article/1468

Thanks for the quick responses. I tried to give him an example of the many homes that we go into where people are having windows replaced, insulation added, and radiant barrier put in place..and that a load calc. could help verify the proper size equipment rather than just replacing with the same tonnage. He just basically said he had "been there, done that" and that I would eventually realize that I didn't need to know this stuff. I agree with you guys, and I will just have to do my own thing.

I know for a fact that 9 out of 10 contractors around these parts don't even have load calculating software much less how to use it

They don't report R and U values for no reason. Fenestration is not some random number thought up to sound cool. They're only a waste of time to people who want to sell the biggest system possible to make the most money they can, screw the end user who has to pay the bills. A load calculation doesn't have to be done every time, on something like a service call, but when the tech can no longer squeeze anything else out of the system and things still aren't right it's a very handy tool. When you do them enough times you'll understand the importance. You may understand the importance right away in the classroom...

If installs are what you do to make a living, you'd better be using it 99 times out of 100. There may be some cases where your gut might have a better idea than software for a certain room, but more often than not, it's what you should be doing.

The only times I'd say you don't need to do a load calc is if you're doing a lot of spec houses (same) for the same builder, you can probably start using some rule of thumb that you learned from the 1st few you did and performed load calcs.