1. Originally Posted by Edgeman
One contractor is proposing a Navien 175BTU CH-210 Combi with tankless DHW or for \$ more a Weil-McLain GV90+5 140BTU mated with an AquaPlus 55 Indirect. I'm think i can scale it back to a Weil-McLain GV90+4 105BTU with an AquaPlau 45 to cut the cost? He suggested the tankless and I suggested a pricing for an indiret instead.
I have no idea why you would want to over size your boiler so much.

The Ultra is a better boiler then the GV.

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Another contractor is suggesting the TT Prestige Excellence PE110 boiler with internal indirect hot water heater. He likes it better than the TT Challenger Combi.

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How do I calculate heat lost base on oil consumption? My energy audit says in 2012 I used 775 gallons of #2 diesel at 79% efficiency. The gov data says that my region had 4753 heating degree days in 2012. I keep the house at 68 degrees. How do I estimate the hourly BTU heat loss from this data?

4. 18,033.87 BTUs loss per HDD. Multiply that times your highest degree day and then divide by 24.

(BTU content per gallon times Efficiency times gallons used) divided by heating degree days.

EG: 140,000X.79=110,600X775=85,715,000/4753=18,033.87X50(50 is just an example I made up for the highest degree day day)=901,693.5/24=37,570.56 BTU an hour loss.

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Originally Posted by Edgeman
How do I calculate heat lost base on oil consumption? My energy audit says in 2012 I used 775 gallons of #2 diesel at 79% efficiency. The gov data says that my region had 4753 heating degree days in 2012. I keep the house at 68 degrees. How do I estimate the hourly BTU heat loss from this data?
As Beenthere has shown in example, 50 Heating Degree Days is an AVERAGE temperature of 15'F ... 7'F low and 23'F high.

Similarly
Using heat content of 130,000 BTU / gallon for fuel oil.
Use 3,600 hours / 150 days as the heating season
Average temperature is about 33'F ... 4,753 HDD equivalent

22,000 BTU/ hr average will be exceeded about 1/2 the time.

I don't have exact temperature bin data
but to illustrate approximate hours of operation for different outside air temps:
……………… 775 ------------ gallons ………… 4785 HDD
…………. 130,000 ------------ BTU per hr / gallon INPUT ………… 150' Days
……………… 79% ------------ efficiency ………… _______ 31.9' less than 65'
………….. 102,700 ------------ BTU per hr / gallon OUTPUT ………… 33.1' average
…….. 79,592,500 ------------ BTU / year …………
…………….. 150 ------------ Days, 4 -5 months heating season ....... 70 Inside
……………… 24 ------------ hours ………… ....... ........ ..... ... 10 Design
………….. 3600 ------------ total hours in heating season ………… 60 dT
………….. 22,109 ------------ BTU per hr average which is NOT that useful
Outside BTU/HR ----------- Hours % load on furnace BTU used at range
50 ___ 8,000 ------------ 900 __ 0 to 25% ………….. ....... 7,200,000 ... 45000...
36 ___ 17,000 ------------ 1,000 __ 25 TO 50% ………….. 17,000,000 ... 36000
25 ___ 27,000 ------------ 1,070 __ 50 TO 75% ………….. 28,890,000 .... 26750
17 ___ 37,000 ------------ 450 __ 75% TO 90 …………..... 16,650,000 .... 7650
10 ___ 45,000 ------------ 180 __ > 90% ………….. ......... 8,100,000 ,,,, 1800
Avg ___ 21,622 --------- 3,600 __ Total Hours . ………….. 77,840,000 ..117200 __32.56

180 hours at > 90% capacity would be ~ 32 days at 5 or 6 hours each day.

Thanks for the info

Peak heat loss is very likely < 50,000 BTU/HR
Last edited by dan sw fl; 02-24-2013 at 06:33 AM.

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7. Using heat content of 130,000 BTU / gallon for fuel oil.
Engineering toolbox list #2 oil at 139,600 BTUs.

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I see only 27 days < 25'F for low temp.
4,125 HDD Oct 15 2011 - April 12 2012

Differential temperature > 43'F for about 160 hours.

Differential Temp = T-stat setpoint [68] - Outside Air Temp

http://www.wunderground.com/history/...q_statename=NA

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From *removed link to HVAC Forum*

BTHU = (Annual Fuel usage/0.6)*(house temp-design temp)*efficiency*fuel heat value)/HDDx24

Where:

68 house temp that we set to
9 design temp from gov data
0.79 efficiency from energy audit
138690 fuel heat value for #2 diesel
775 fuel usage from energy audit/oil company logs
4753 Heating Degree DaysHDD from gov

yields = 73,197 BTU loss per hour

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The efficiency number from the energy audit is what is skewing the numbers. That is combustion efficiency not system efficiency. At 2000 sq. in Groton, around 40,000 sounds about right. The Slant Fin program works and has a fudge factor included in it.

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Originally Posted by Edgeman
From *removed link to HVAC Forum*

BTHU = (Annual Fuel usage/0.6)*(house temp-design temp)*efficiency*fuel heat value)/HDDx24

Where:

68 house temp that we set to
9 design temp from gov data
0.79 efficiency from energy audit
138690 fuel heat value for #2 diesel
775 fuel usage from energy audit/oil company logs
4753 Heating Degree DaysHDD from gov

yields = 73,197 BTU loss per hour
Annual Fuel Usage / 0.6 ... Now T H A T'S one helluva Fudge Factor !
1/ 0.6 = 1.6667 ...NOTHING like adding 67% to the Appropriate result _ 43,918 BTU/Hr

12. Originally Posted by dan sw fl
Annual Fuel Usage / 0.6 ... Now T H A T'S one helluva Fudge Factor !
1/ 0.6 = 1.6667 ...NOTHING like adding 67% to the Appropriate result _ 43,918 BTU/Hr
But it will never under size a unit. ROFL

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Originally Posted by beenthere
But it will never under size a unit. ROFL
No, but it may very well get one operating times that MANY would Not be real pleased with.

OR a calculated 100,000 * 1.66 ... 166,000 .:. you can have at least 2 units.

Are mechanical contractors now selling 2 for 1 [ BOGO ] like you see in the grocery store?
I'll plan on the _GET ONE_ when my neighbor does the _BUY ONE_ portion.

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