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Old 05-12-2009, 07:50 AM   #16
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Sizing a furnace - can't find one small enough


"The projects never end and the vacation never begins".

I know, I have the same problem. Always trying to get "ahead". Of what I don't know, supposedly the next guy.

Cheers

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Old 05-12-2009, 08:41 AM   #17
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Sizing a furnace - can't find one small enough


Best bang for the buck- Seal and Insulate everywhere, put a radiant heat barrier in the attic to cool down the wife, put in ceiling fans, super-insulate the attic.
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Old 05-12-2009, 01:39 PM   #18
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Sizing a furnace - can't find one small enough


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Originally Posted by Jim W View Post
heat loss to be 29,198 BTUH.
29,000 BTU/Hr = 8.5 kW heater = ~ 9 toasters.
The average house elec. usage is 1 kW and this mostly goes into heat so go with 8 toasters. If you have 10 sedentary people in the house you could go with 7 toasters!

A heat pump would take about 3 kW, 10A @ 240v.
I'd go with elec. zone heating.


Now I have all of three more-or-less valid data points

SW Ontario, Canada
398.7 cubic meters = 140 therms of NG in 28 days = 5 therms/day
2900 sq. ft. gives 5/2900 = 170 BTU/day/sq. ft.
664 HDD/28 = 24 HDD in one day
170/24 = 7.1 BTU/day/sq. ft./HDD

Wash, D.C.
838 therms of NG in 90 days = 9.3 therms/day
3100 sq. ft. gives 9.3/3100 = 300 BTU/day/sq.ft.
2658 HDD/90 = 30 HDD in one day
300/30 = 10 BTU/day/sq.ft./HDD

San Diego, CA
29,000 BTU/hr = 21 therms/30 days = 0.7 therm/day
1560 sq ft gives 0.7/1560 = 45 BTU/day/sq.ft.
270 HDD/30 = 9 HDD in one day
45/9 = 5.0 BTU/day/sq.ft./HDD

27 more picked at random and I'll have a statistically large sample!

Last edited by Yoyizit; 05-12-2009 at 02:11 PM.
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Old 05-12-2009, 02:51 PM   #19
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Sizing a furnace - can't find one small enough


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27 more picked at random and I'll have a statistically large sample!
Of useless bad rule of thumb sizing.
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Old 05-12-2009, 03:33 PM   #20
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Sizing a furnace - can't find one small enough


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Of useless bad rule of thumb sizing.
Humor me

Somebody probably has published heat gain for an average house vs. solar insolation, which will be the next refinement to this method.
Insolation for cities is already on the Web.
Perfect absorption of sunlight by house walls and roofs would give 90w for each sq. ft..
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Old 05-12-2009, 03:40 PM   #21
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Sizing a furnace - can't find one small enough


There is no average house.

A 2400 sq ft rancher usually has a higher heat loss an gain then a 2400 sq ft 2 story.
While a 3000 sq ft 2 storu can have the same load as the 2400 sq ft rancher.

What size is an average house?
How many windows does an average house have.
What color are the shingles of the average house.
What color is the siding of the average house.

The word average, is misused when it comes to many things.
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Old 05-12-2009, 04:07 PM   #22
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Sizing a furnace - can't find one small enough


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There is no average house.
You're right. This is a mathematical model of an average house, just like 5'9" was the average height when I was born.

A 2400 sq ft rancher usually has a higher heat loss an gain then a 2400 sq ft 2 story.
While a 3000 sq ft 2 storu can have the same load as the 2400 sq ft rancher.
Well, if people tell me what style house they have, I can mush that into the numbers. For now I'm only doing heat loss and HDD.

What size is an average house?
In this case, 2520 sq. ft.

How many windows does an average house have.
Mine has 19. If people tell me how many windows they have, I can mush that into the numbers.

What color are the shingles of the average house.
Well, you have the choice of red, orange, yellow, green, blue, violet or some combo [i.e., the visible spectrum] but emissivity is more important.

What color is the siding of the average house.
See above.

The word average, is misused when it comes to many things.
I intend not to misuse it!

The average for these three houses is 7.4 BTU/day/sq. ft./HDD, so you can already figure out if your house is above or below this "average" just using readily available data from your utility bills, the Internet, and some calculations.
If I still had Manual J from the library I'd use their house data to make a fourth sample.

Your spreadsheet may calculate Standard Deviation but not all do. Two standard deviations for a normal distribution take in ~95% of all data points.
If this heat loss is Normally Distributed and this sample is representative, then ~95% of the houses in North America are between 3.4 and 11 BTU/day/sq. ft./HDD.
An average is a Point Estimate. The 3.4/11 is an Interval Estimate, to some Level of Confidence.

100x (7.4-3.4)/7.4 = 54%, so it's 7.4 +/-54%, a pretty wide tolerance. In this tolerance are all the things you mentioned; style, # of windows, color, prevailing winds, insolation, snow cover, landscaping, all of it.

My 1964 house doesn't do so well by this standard, so I guess I should also ask for the age of the houses. I probably have infiltration due to settling.

Last edited by Yoyizit; 05-12-2009 at 04:38 PM.
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Old 05-12-2009, 04:39 PM   #23
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Sizing a furnace - can't find one small enough


Might as well stand on the sidewalk across the street. Hold your hand 6" infront of your face. However many fingers it takes to cover the house, that how big of a boiler you need in sections to heat the house.

The old saying is: There aren't to many houses a 10 section boiler won't heat.
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Old 05-12-2009, 04:48 PM   #24
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Sizing a furnace - can't find one small enough


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Might as well stand on the sidewalk across the street. Hold your hand 6" infront of your face. However many fingers it takes to cover the house, that how big of a boiler you need in sections to heat the house.

If it works better than +/- 54% I'm up for it, and I don't even need a calculator.

The old saying is: There aren't to many houses a 10 section boiler won't heat.

How many therms/hour is that?
I hope there are more houses like mine in North America; right now I'm at the extreme end, and not the good end.

Always a pleasure conversin' wit' ya', Mr. There

Last edited by Yoyizit; 05-12-2009 at 04:50 PM.
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Old 05-12-2009, 05:06 PM   #25
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Sizing a furnace - can't find one small enough


Depends on brand and model.
500,000 plus BTUs.

Or 5 therms plus an hour.

Lots of houses have boiler that big. And don't need that much heat.
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Old 05-12-2009, 08:03 PM   #26
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Sizing a furnace - can't find one small enough


"29,000 BTU/Hr = 8.5 kW heater = ~ 9 toasters."
I dunno Yoyizit, seems like running 9 toasters all day could get expensive.
- unless I had natural gas toasters
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Old 05-12-2009, 08:11 PM   #27
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Sizing a furnace - can't find one small enough


Quote:
Originally Posted by Jim W View Post
- unless I had natural gas toasters
I guess they use those little canisters, like the lighters that run on butane.

Depending your local prices, take your pick

1 Therm of energy
=~0.9 gal of fuel oil
=~70-100 cubic feet of natural gas
=~1.1 gal of propane
=~29 kwh of elec heat
=~8.4 kwh of heat pump heat
=~14# of wood

And, average solar insolation in kilowatt-hours per square meter per day for CA is 6.

Last edited by Yoyizit; 05-12-2009 at 08:29 PM.
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Old 05-12-2009, 09:26 PM   #28
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Sizing a furnace - can't find one small enough


Oil would be .71 gallons to equal a therm.
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Old 05-13-2009, 02:47 PM   #29
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Sizing a furnace - can't find one small enough


Quote:
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Oil would be .71 gallons to equal a therm.
1 Therm of energy can be had from approx. 0.71 gal of fuel oil, 100 cubic feet of natural gas, 1.1 gal of propane, 29 kwh of elec heat, 8.4 kwh of heat pump heat or 14# of wood
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Old 05-13-2009, 07:59 PM   #30
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Sizing a furnace - can't find one small enough


Quote:
Originally Posted by Yoyizit View Post
1 Therm of energy can be had from approx. 0.71 gal of fuel oil, 100 cubic feet of natural gas, 1.1 gal of propane, 29 kwh of elec heat, 8.4 kwh of heat pump heat or 14# of wood

This is a great statistic. Thank you!!!

I have several areas of my website and daily calls that this info will come in VERY handy. I knew that I had this given to me several years ago in training, but had forgotten that comparison and have since misplaced.

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