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# heat loss calculation how to

Member Posts: 2
its been a long time since i calculated a heat loss for a building. shame on me! have used budget numbers for years. now i have a commercial building which is brick. they want the BTU size tomorrow and i need to know where i can go to get a form pdq. thanks bix jogger dec 14 monday

• Member Posts: 395
Remember the golden rule

The ones that demand the most are always the one that will only pay the least.

Let look at this another way.if they really wanted you to have any chance at getting this job they would have gave you more time to bid the job properly.

This is one you should pass on or call them backup and tell them it will be about eight hundred dollars to have the numbers to them by tomorrow.

You can go here [url=http://www.hvaccomputer.com]www.hvaccomputer.com and they made be of some help.

Hope this helps.Hate seening anyone get abused.
• Member Posts: 5,853

A/RX Delta T = btuH conductive loss.

Where A = Area, R = resistance value, and delta T is the design heating temperature difference between inside and outside.

Calculate volume of building, figure out required or natural air changes per hour, and use the following formulae for infiltration and mechanically induced air changes,

ACH X .018 X delta T = btuH for air changes. If in doubt, spend the money necessary to perform a blower door test, and fine tune that number, because it is the ONE thing that CAN and WILL come back to bite you in the butt.

If you know the U value of windows, invert it by taking 1 and dividing it by the U value to get it to an R value.

It don't get much simpler than that. All you need is a tape measurer, a calculator, a legal pad and pen, and someone to help you measure the building.

ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
• Member Posts: 5,853
PS...

I agree with don. Nothing is free...

It will also tell you how they deal with their other subs as it pertains to money.

ME
It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
• Member Posts: 48
heat loss calculations

got my HVAC salesman from the wholesaler to do a manual J which i havent done for 25 yrs, i have to admit. you know my budget numbers for BYU'S per sq ft were rite on, though.

thanks for the input.

at one time i had a slide rule that let me enter in all the walls, ceiling, floors & infiltration with the U valves printed on it. does anyone know where something like that is anymore? it was indeed like "Rolling ur own Manual J"

bixjogger dec 15 2009
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