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# Heatloss Calculation

#1
06-18-09, 08:56 AM
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Join Date: May 2006
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Heatloss Calculation

In the Important Information before buying a new boiler sticky above, it states that a Heat Loss Calculation is "definitely something you can do yourself."

I'd love to. Where can I find detailed instructions on how to do this myself? And what kind of equipment do I need?

How can I translate the heat loss calculation into the size of boiler I should be looking at?

Thanks

#2
06-18-09, 09:55 AM
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Location: San Jose
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It used to be far easier when SlantFin had the Heatloss Explorer program available for a free download.

You could try searching online...

[online heatloss calculator]

[online "manual j"]

The heatloss calculation will give you the size you need although it includes a very robust recovery fudge factor that in reality you most likely wouldn't need.

#3
06-19-09, 08:03 AM
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Join Date: May 2006
Posts: 87

Most of the online calculators are from Britain and calculate in metric and the output is in kWh?

Anyway... next question. When calculating the square footage of the home, does one include the basement?

My house has a full basement, uninsulated and not heated. The boiler is located in the basement and the heat radiating off the boiler keeps the temp down there comfortable. Since there are no radiators down there, do I include it in the sqft calculation?

And do we use internal or external dimensions?

#4
06-19-09, 03:43 PM
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One kilowatt hour is equal to 3,412 BTUs

#5
06-20-09, 07:19 PM
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Do not calculate the basement if you are not heating it but you will calculate the rooms abaove as above unheated basement.
When the boiler is replaced the basement will be cooler.
http://www.comfort-calc.net/faq.html

#6
06-22-09, 01:36 PM
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Does anyone know why Slantfin removed it? I have the CD and would be willing to burn and send it to you as long as you do the same if someone else needs it.

John

#7
06-24-09, 11:19 AM
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I dont know if it's legal but there are sites that let you store such big programs online and figured someone would upload it..but it's probably not legal or someone would have dont it already.

And you cant email such a large attachment if you wanted to. But it's a fantastic program!

#8
07-06-09, 07:34 PM
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Join Date: Jul 2009
Location: Massachusetts
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Heat Loss Calculator

I found this but I am having a hard time using it since I really don't know the R-values for my 1950 home.

Home Heat Loss Calculator

#9
07-07-09, 04:38 AM
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Originally Posted by 1950original
I found this but I am having a hard time using it since I really don't know the R-values for my 1950 home.

Home Heat Loss Calculator
i took a peek at the help screen there so maybe you can use some conservative values. Or to be absurdly generous you can just assume no insulation anywhere etc.. .that will be the worst heat loss you can calculate then just see where you stand and adjust from there.

even when i used the slantfin program, i had no idea what's in my walls etc so usually just choose the worst option for each.

#10
07-07-09, 06:00 AM
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Everything has an R-value including air films on walls. A better program will allow you to create the R-value. As far as insulation in the walls a 1950's home was built with none. What was added to the outside if anything. Is it insulbrick, siding maybe with foam underneath or multiple rows of brick? You have to determine the wall contraction.
The better programs have enough fluff in them already, maybe 15-20%, and the quickie ones like in the link just add more fluff for CYA.
The information inputted makes a difference. If not inputed properly it can throw off the calculation.

#11
07-07-09, 07:13 AM
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Join Date: May 2006
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Thanks for the great information everyone.

I ended up getting a professional heat loss calc done. I am going to try and double check the values but I pretty much am going to trust the one I got.

I think an online calculator is great as a starting point. When I started getting estimates for 150,000 + BTU boilers for my 1000 sq ft home, it really helps to know a ballpark.

I had around 80,000 from an online calculator (I entered in rough guesses for some of the numbers) but my professional heat loss showed just under 40,000. I was surprised! Either way I knew that 150,000 + was way too big.

Thanks

#12
07-07-09, 08:26 AM
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Originally Posted by avatar

I had around 80,000 from an online calculator (I entered in rough guesses for some of the numbers) but my professional heat loss showed just under 40,000. I was surprised! Either way I knew that 150,000 + was way too big.

Thanks
Think of all the \$\$\$ you will be saving

I know before i found this forum, i had no idea that a 225K boiler was enough to heat an apt building Good riddance to that old beast. (or i guess i could have added a nice addition on now that i think about it)

Just curious, how much did it cost you for the loss calculation?

#13
07-07-09, 08:57 AM
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I'm surprised to see a HC that low. A 50's home in Mass even at 1,000 sq ft would have needed some decent upgrading to do that well. Could you share some of the numbers, window specs, foundation insulation, air sealing and such. Just thinking about a reality check.

Bud

Last edited by Bud9051; 07-07-09 at 09:19 AM. Reason: correction
#14
07-07-09, 11:32 AM
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Join Date: Jul 2009
Location: Massachusetts
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Originally Posted by Bud9051
I'm surprised to see a HC that low. A 50's home in Mass even at 1,000 sq ft would have needed some decent upgrading to do that well. Could you share some of the numbers, window specs, foundation insulation, air sealing and such. Just thinking about a reality check.

Bud
I got 146,000 for my 3700sf (including basement) 1950 house in MA using the online calculator with the following inputs:
Design outdoor temp: 0
Heating degree days: 6250
Ceilings: 1211sf at R-20
Walls: 3414sf at R-3.4
Windows: 304sf at R-1.8
Slab on Grade: 159ft perimeter at R-0.47
Infiltration: 28,408cu ft at 1.0 air change/hour
Internal heat gain: 4 occupants

#15
07-07-09, 12:40 PM
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Join Date: May 2006
Posts: 87
Here is a free heat loss calculator tool. I haven't used it nor any other heat loss program so I can't say how well it works (if at all) Water Load Calculator

Try as I might, I can't find the online calculator I used. It was VERY simple and rather than selecting R-values, you selected the amount of insulation (none, poor, good, excellent, etc).

Anyway my design temp is -4F, my home is a 1.5 storey 1950's frame house with a full uninsulated basement and only 6" of insulation in the attic. Dimensions are 739 sq ft mainfloor and 326 2nd floor. (Internal dimensions). There are 14 windows and 3 doors. Professional came back with just about 40,000 BTU/hr heat loss and 12.5 ACH. Does that sound way off?

#16
07-07-09, 02:02 PM
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I'm getting lost with the two posters. Avatar, if you are in sw ontario, when I check the HDD I get just under 6,000. Yet when I check state side, Grand Forks, ND, south of your location, I get over HDD=10,000 so not sure what number to use. The 12.5 ACH isn't right unless one of the doors stays open 24/7. And there are several other parameters needed, sloped ceilings, exposed foundation walls, wall insulation or construction, yada, yada. Did they do a blower door test and maybe that 12.5 is an ACH50 number?

I'll wait for some of the pro's to weigh in, as most can look at the numbers without a calculator and guess very well.

1950original, your numbers need some work, but best to start a new thread. I have used that calculator for energy performance, but not sure if it is suitable for heat load calculations. Glad to help on another thread.

Bud

Last edited by Bud9051; 07-07-09 at 02:05 PM. Reason: add
#17
07-07-09, 03:07 PM
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Where in Southwest Ontario are you? The OD design temps vary widely in Ontario.

#18
07-07-09, 05:28 PM
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Originally Posted by avatar
How can I translate the heat loss calculation into the size of boiler I should be looking at?
They are equal. The USDOE rating should equal the calculated heat loss.
Doug

Last edited by NJT; 07-10-09 at 06:26 AM.
#19
07-08-09, 07:03 AM
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#20
07-09-09, 05:53 PM
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Check out Taco's free load calc tool:

#21
07-10-09, 11:19 AM
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Originally Posted by Bud9051
I'm getting lost with the two posters. Avatar, if you are in sw ontario, when I check the HDD I get just under 6,000. Yet when I check state side, Grand Forks, ND, south of your location, I get over HDD=10,000 so not sure what number to use. The 12.5 ACH isn't right unless one of the doors stays open 24/7. And there are several other parameters needed, sloped ceilings, exposed foundation walls, wall insulation or construction, yada, yada. Did they do a blower door test and maybe that 12.5 is an ACH50 number?
Grand Forks, ND is not close to me; I think it's under Saskatchewan (which is Northwest of me). Anyway, I live on the Ontario/Michigan Border in Sarnia which is very close to Detroit. The design temp the pro used was -4F. I do not know my heating degree days for certain, but this document: (https://sfis.edu.gov.on.ca/Download/...llocationE.rtf) has it at 3928.

He did a blower door test. ACH was "air changes per hour at 50 Pa"? iirc.

Hope that helps........

#22
07-10-09, 12:51 PM
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Location: New England
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Hi again,
If your 12.5 ACH was at 50 Pascal then simply dividing by 20 will approximate your natural air exchange.

The HDD you have may be in Celsius. If so multiply by 1.8 for fahrenheit.

If the guy did a blower door test, I have to say he should know what he was doing. Without more specific details I can't suggest a different number.

I would still recommend having a Manual J done by a heating guy in your area.

Bud