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# Heat loss calculation

## Heat loss calculation

#1
10-15-19, 08:22 PM
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Heat loss calculation

Hello ! I am trying to use the slant fin calculator to size a new oil boiler and need help. What indoor and outdoor temp should i use ? If i use 70 indoor 8 outdoor 66 400 btu comes up. 75 in 5 out jumps to 82 000 btu. This obviously is a big difference.

Also, i Have a 460 sqft garage that is insulated with heavy ceiling insulation and r19 stud/plaster walls with brick exterior attached to my house.
I have a 4ft baseboard heater connected to the house heating system. Oil boiler hot water. I only want the garage to not freeze and it has not. . But its been close. I think another 4ft baseboard heater would be better.
my question is how do i calculate the btu to keep garage above freezing to add to my slant fin calculations?

#2
10-17-19, 11:48 AM
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Could I please get some help with what the indoor and outdoor temperature input should be on a slantfin heat loss calculator?

Is this just the published design temp from energystar?

thank you

#3
10-17-19, 03:55 PM
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For outside design temp, use the 99% value for your location (for Pittsburgh, it's 7 deg F). For inside, use 70 deg. Tell us your sq ft of the house for a sanity check.

For the garage, use whatever minimum inside temp you want to design for. I assume that the garage will be on its own zone with its own thermostat, right? What are you going to set that thermostat at? That's the indoor temp you should use for calculating the garage heat loss.

Last edited by gilmorrie; 10-17-19 at 05:00 PM.
#4
10-17-19, 04:28 PM
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total square foot, basement (heated) and floor above 3600.
I am near Pittsburgh, PA, energy star says use 11 degree

#5
10-17-19, 04:31 PM
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and gilmorrie, thanks for the help !

I am getting around 110,000 to 120,000. I have a pretty well insulated home, but there is a cathedral ceiling over living and dining room. thinking about a Buderous oil fired boiler

#6
10-17-19, 04:54 PM
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and gilmorrie, thanks for the help !

I am getting around 110,000 to 120,000. I have a pretty well insulated home, but there is a cathedral ceiling over living and dining room. thinking about a Buderous oil fired boiler

#7
10-17-19, 05:37 PM
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Double check your calcs. 110-120 sounds too high to me. The basement sq ft doesn't count as much as above grade.

Last edited by gilmorrie; 10-17-19 at 06:15 PM.
#8
10-17-19, 06:54 PM
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my basement walls are block with only fir strips and thin panelling. total length 174 ft.
115ft. is total beneath grade. when they ask for exposed walls, in slant fin calc. are walls below grade exposed?

#9
10-17-19, 08:27 PM
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so I went over my calculations mostly accounting for the basement walls are mostly below grade. I changed the garage indoor temp to 38 degrees, which keeps it above freezing (my goal).

depending on where I put my outside temperature either 9 degrees which is what my area calls for, or a bit lower at 5 degrees, I now come up with 87-92K.

This seems more reasonable to me.

#10
10-19-19, 01:26 PM
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output boiler 100k and dont split hairs.

#11
10-20-19, 08:51 PM
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thanks for the input about the output !

#12
10-20-19, 09:21 PM
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simple calc that works is 3600x25 btu per sq ft. Thats 90k.

But how much and what type of heat emitters do you have?

No sense putting in 100k boiler if you have 50k of heat emitters

#13
10-21-19, 04:31 AM
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With baseboard all ready installed
174 ft x 600 Btu per ft
Comes out to 100k Btu. Output
done

#14
10-21-19, 06:42 AM
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I have 160ft baseboard. I did the slant fin heat calc. for the numbers I came up with.
when I went back over the calculations, I made some adjustments to the basement heat loss, because I had misrepresented the concrete slab floor and some external walls which are at least 70% below grade.

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