BTU Calcs and sizing. Help

I am normally good at finding this stuff on here, but have searched and can't really find it...I have tried many online programs for BTU Heat Loss calcs.

Anyone have a reference for a good heat loss BTU calculator, so I can figure out what I really need.

I have numbers all over the map for the same size room, etc....

Example:
Here is one room
7' w x 12' L x 8' H, 1 Window (Double pane, UV/Argon), 1 outside wall, and good insulation. (0 Deg. F outside - 68 Deg. Inside design temps)
BTU anywhere from 1525-6078 using different online programs. (makes a big difference in the baseboard size and boiler sizing).

I was using around 480 BTU/Foot for my calc for baseboard lengths.

What would you guys come up with or use?

Thanks!

The best method for determining building heat loss or heat gain is the Air Conditioning Contractors of America procedure. It's know as Manual J and its us is a requirement in many building codes. In Maryland it's also a requirement whenever an A/C condensing unit is replaced. See: http://www.acca.org/ Do a search for Manual J. The books are expensive and the procedure has a steep learning curve. The Manual J books come with a Excel spreadsheet that does a heat gain/loss calculation. At one time the xls file was on their website. I can not find it now. Companies selling analysis software to the construction trades take the ACCA spreadsheet and add a user friendly interface to it. I'd suggesting finding a local contractor with such software and just hire them. Be sure the software they are using is ACCA approved and it is the current Manual J, version 8.

Some info here

http://www.mrhvac.com/loadcalcshortform.htm

http://www.filebuzz.com/findsoftware/Ma ... tor/1.html

http://www.hvaccomputer.com/gtarget1.as ... 5QodzReMiw

http://www.load-calculations.com/

they usually figure 580 btus @180* @ 4 gpm per lin.' of bb

Thanks! I will try that. I was going on the lower side to be safe. I found some formulas and doing some calculating.

Does the element size matter much at that temp. I see the BTu rating is the same 1/2" vs. 3/4" element size.

Here the rating chart, you are correct.
http://www.slantfin.com/documents/326.pdf

if you figure wrong you can always increase the temp also if you raise the bb off the floor 14 to 16 inches you almost double the output looks like hell but it works

The BTU calculators others have suggested are frankly worthless. They make lots of assumptions, assumptions they don't tell you about. If you want a heat loss value that has some hope of being close to correct you need at a minimum the following inputs:

Indoor design temperature
Outdoor design temperature
Exposed wall area
Window area
Exposed door area
Exposed ceiling area
Insulation R values for each area
Floor type, framed, slab on grade, basement, etc.
Air infiltration (i.e. exchange rate)

If the calculator you are using doesn't ask for these values it's not worth much. While the list I provides would provide a reasonable heat loss estimate it would not be appropriate for A/C heat gain. That also requires a sun loading input. Air infiltration has a big effect on heat loss, it can be small for a well constructed home and like an open window for a poorly constructed one. Since it is difficult to determine many calculators simply ignore it.

A heat loss only calculator comes with the Siegenthaler's book. See the publications section the his web site: http://www.hydronicpros.com/

Other useful books and full versions of software are offered. A screen shot for a heat loss calculation using the software that comes with the book is show below.

The long and short of it is buy the book.

yanche; do you have any info on the newer fuel oil & diesel blends they are comming out with and are going to mandate their use in the comming years looking for btus per gal ect.thanks jim

Slant-fin used to have a great program called Hydronic Explorer. It was free either on CD or as a download. I used it when I installed an EFM 520 with three new zones in my house. They quit making it, because I couldn't find it when I was looking a few months ago. I actually found a web forum where someone in senior management had promised to find some CD's and send them out upon request, but when I called the company, I didn't have any luck. They did email me some worksheets that worked well, though. If you're just doing one house, figuring it by hand isn't too bad.

The hvac computer systems link is true Manual J. It's a fifty dollar fee for thirty days use. I used it and it allowed me to provide all of the inputs Yanche described and it gave me a room requirement for each room. I then took that information and other information available on the 'net and used it to size and match new and old cast iron radiators to room requirments. I had no issues. The program is very flexible and allows you for example to breakdown a wall into its various construction components by sq footage to calculate an accurate heat loss.

I found this one online, and has many inputs as to insulation, windows, etc....It states uses Manual J for calcs.
http://www.warmlyyours.com/hlc/room/room_general

I ran my living room:
14' x 28'
6 Windows (29" x 60"), Low E, PVC
2 Exterior Walls (8'x14') (R11, clapboard siding/plaster-lathe interior)
Carpet (Unheated basement but with R11 insulation)
overall Insulation - Average
Temp. Location - Buffalo, NY
Outside temp Difference - 0 Degrees, 70 Inside

Came up with approx. 7,777 BTU/Hr heat loss. (Add 20% for error/misc. = 9,332 BTU/hr).
Does that seem in the ball park for that size of a room?

Therefore, 9,332 BTU/hr / (480 Btu/hr at 160 deg. per foot baseboard) = 19 Feet. (I know they use 180, but I want to make sure I have enough if I run at lower temps).

Thanks!!

I worked through a sample calculation. It's the best free to use heat loss calculator I know of. One could do an entire house one room at a time and then total the results for sizing a boiler or furnace.

It's a reasonable heat loss calculator that addresses all of the criterion I suggested. It's likely based on ACCA's version 7 Manual J, not the current version 8 Manual J. Still if the math calculations are correct it should give a reasonably accurate answer. The references to window and door sizes should be entered in rough-in sizes. The state and location setting are for determining wintertime low temperature conditions as referenced in the ASHRE manuals. AP = Air Port. Use the coldest closest listing to your homes location.

On copper tube fined baseboard you should de-rate the manufacturers published specs by 15%, i.e. divide by 1.15. This removes a build in IBR specification bias which makes the baseboard appear more capable than the actual laboratory test results. I'd use slightly different rating numbers for the baseboard. For example see Slantfin Fine?Line 15 at: I worked through a sample calculation. It's the best free to use heat loss calculator I know of. One could do an entire house one room at a time and then total the results for sizing a boiler or furnace.

It's a reasonable heat loss calculator that addresses all of the criterion I suggested. It's likely based on ACCA's version 7 Manual J, not the current version 8 Manual J. Still if the math calculations are correct it should give a reasonably accurate answer. The references to window and door sizes should be entered in rough-in sizes. The state and location setting are for determining wintertime low temperature conditions as referenced in the ASHRE manuals. AP = Air Port. Use the coldest closest listing to your homes location.

On copper tube fined baseboard you should de-rate the manufacturers published specs by 15%, i.e. divide by 1.15. This removes a build in IBR specification bias which makes the baseboard appear more capable than the actual laboratory test results. I'd use slightly different rating numbers for the baseboard. For example see Slantfin Fine?Line 15 at: http://www.slantfin.com/cgi-bin/specifi ... fineline15. Click the "rating chart"
You could also correct for water temperature cooling effects as the water progresses in the baseboard. Plan your supply water flow direction so that the hottest water gets to the greatest heat loss location first.

I have the Slantfin Heat Explorer install file and it's manual in pdf format.

I would be happy to supply the forum a copy.

Thanks Mike.!

I am on my way for calculating my BTU requirements. I was pretty close to my other calcs using this SlantFin program....will advise results.