BTU's per square feet

[hcong]

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.

Here in California, plan checkers are becoming strict and asking for Manual D & J. For energy purposes, the state won't let you install a new HVAC without load calcs and making sure the unit is not oversized.

[courttech]

yes, I am experiencing the same thing here in the west coast of canada...basically same climate as seattle, inspectors wanting heat loss/load calculations...not that they know if they are right or not. But to get down to the accurate numbers takes getting so much info from the general contractor in regards to the materials used in the construction of the building that a day can be spent on just gathering info..adding cost to the quote that the puts your bid over the competition. If it was a blanket policy throughout each district/province/ state then we would all be on the same page for costs...until then...get the quote out based on past experience and carbon copy the heat load calculations unfortunately.

[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.
It's done in commercial buildings, at least larger ones and as long as building performance is an issue I think the design should be where it belongs, with the designer.
I'd bet one thing that would disappear if design/performance were an issue would be flex duct snaked all over an attic.

[Juan Madera]

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.

[ICanHas]

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.

[dlove]

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.

[hvacmike85]

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

[meplumber]

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.

[beenthere]

ACCA manual N is for commercial.

[meplumber]

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.

[Willserve]

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

[Mr Bill]

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.

[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?