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Originally Posted by Matt_M

What kinda of load calc software are you guys using?

Wrightsoft for residential
Trane Trace 700 for commercial

Originally Posted by beenthere

R9 to R11 depending on stud center and siding.

Thank you

Where's bunny?

Most will figure 500 sq ft per ton, but also U will need to consider lots of factors. Cause I have been many homes with lots of windows and very high ceilings and that figure want work. Also some units that are too tight with today's technology of foam insulation will cause problems for size of units. Just my thought on the subject. Good luck

R9 to R11 depending on stud center and siding.

Originally Posted by zxcb

What do you guys use for a wall R factor in old houses when the HO has no idea what insulation is in the walls?

Anyone?

My 2000 sq ft house has a cooling load of 1.5 tons - you are not going to get a return call if you ROT a 3.5 to 4 ton price at me. Just sayin.....

I get the whole "quote over the phone" thing for people who are just price shopping but on a sales call - a quick load calc is not that hard to do. You can adjust from there if you get the job. My experience is there are quite a few contractors out there that will ballpark something and install inappropriate size equipment. The way homes and equipment are being built today, it is harder to just make a guess at what you need. As an aside, we do have the luxury in Indiana of not having a statewide heating and cooling contractor licensing requirement. What fun when you get into rural areas.

The other thing we should be doing as contractors is evaluating the structure and making recommendations on energy efficiency improvements so we can make the equipment smaller. Better for everyone.

rhvac.

What kinda of load calc software are you guys using?

A load calculation is best IF you don't fudge input numbers to get the answer you want. Newer homes in our area can be as little as 1,000 sqft per ton, 800sq ft per ton is common. Older homes and upstairs units can go as high as 350sq ft per ton. Unfortunately "rule of thumb" 500sq ft per ton is what typically gets installed regardless of actual load...

On the heat side pick the smallest capacity furnace that has the blower size you need for A/C, it's more than enough heat for just about any southern home.

What do you guys use for a wall R factor in old houses when the HO has no idea what insulation is in the walls?

Originally Posted by hvacker

I think ROT's are used much more often than actual loads. So called "older guys" will say they've been doing it this way for years and why should I tie up my time with a load just to lose the job to another contractor.I think younger contractors are much more likely to do a load because they are more familiar with computers and more comfortable with the results.

This is becoming the biggest line of BS I have ever seen, hacks are not determined by age, their determined by mentality or capabilities, you come to Houston and I can show you two old dudes, to one young guy, that actually does a load calculation. I saw a sting on Channel 11 here in Houston about a month ago, guess what! all the crooks and hacks in the sting were probably under 30, go figure! This "old school" crap about the old school dudes is really getting old, some of us have come around, quit the dang stereotyping.

Originally Posted by hvacker

I think ROT's are used much more often than actual loads. So called "older guys" will say they've been doing it this way for years and why should I tie up my time with a load just to lose the job to another contractor.
I think younger contractors are much more likely to do a load because they are more familiar with computers and more comfortable with the results. Computers seem like a natural place to get information for them.
I often see posts here looking for load software when it's just as ez with a simple paper form but they've learned to trust computers. I'm sure it's easier to get an older contractor to use the paper form than a computer. Different generations.
I wouldn't expect many older contractors to change any time soon. Their system will probably work ok and no one's going to yank it out to show how a different system will be better as long as the house is fundamentally similar to those where ROT worked before.

What is the Rule of Thumb to determine if you fall into the "older guys" category? Is that an actual age or mentality Lol

True. I forgot about Manual N. I use WrightSoft's RightSuite Universal. We also have HVACalc. It is a much simpler residential/light commercial heat loss/gain program. We only use it for little projects that don't need all the bells and whistles that we get from RightSuite.

ACCA manual N is for commercial.

Mike, actually, Manual J is for residential only. For commercial, there are (2) accepted methods, ASHRAE RTD and ASHRAE CLTD. These methods factor in required ACH and required ventilation applicable to the commercial and institutional market.

what program or method do you guys use for load calculations? Are commercial calcs easy once manual j is learned

Originally Posted by hvacker

I think the fair way to do a design/load estimate would be for the responsibility to fall on the Architect/engineer, house designer. They have the responsibility for the integrity of the building and have been putting the responsibility on the trade for too long.

Diamond in the rough. I deal with A&E's a lot. Not all have a clue how to design a system outside of a text book. But we need them. And most of the time they get by. But you would be mistaken if you don't have the HVAC vendor and GC look over the drawings as well.

Its a shared responsibly.

Can this question even be answered?

Isn't this like asking.. the person weighs 150 lbs
how many Calories does he need to eat every day to maintain his weight?
There are so many variables that you can't possibly give one simple answer.

My rule of thumb in sizing is use manual j and then pick the smallest system that will fit the bill! I tend to (slightly) undersize as it adds comfort, reliability, economy of operation and lastly, customer satisfaction. I think we ALL tend to add just a little to make sure we are covered. This, i believe, includes the #'s you get from man J.

Have installed 50k BTU furnaces in 1800 foot split entries (900' per floor) in Montana and had nothing but praise for how even the temperature was throughout the home in the coldest weather.

Keep in mind that Man J does not include internal gain in heating calcs.