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05052011, 07:54 PM  #1 
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Help with daily actual output from the furnace
Hello Sir,
I have very old Gas furnace: LENNOX gas furnace Model: G20Q3/4E1003 Made on year 1990 The Furnace capacity =100,000 Btu/hr. My house is 30 yrs old, 2008 square feet. I got the gas usage 263 ccf during 41 days from 02/24/11 to 04/06/11. The total heating degree days were 1183 during this period. The house inside temp was about 67 F. Does anyone know how to calculate daily actual output from the furnace? Is there any equation for my reference. Thank you in advance! 
05062011, 04:58 AM  #2 
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Help with daily actual output from the furnace
While dividing therms by number of days gives a 6.41 therm per day average. Without knowing actual temps of each day. No way to know for anyone day, let alone the coldest day you had.

05062011, 08:23 AM  #3 
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Help with daily actual output from the furnace
To satisfy your request a very lengthy explanation would be required, a more accurate accessment of the energy required to heat your home would be arrived at by doing a heat loss analysis whereby you evaluate the insulation quality of your entire building otherwise known as a "Manual J".
This link may help you understand the relationship of Heat Degree Days as it relates to heating requirements http://en.wikipedia.org/wiki/Heating_degree_day I know if you search there are programs which are free to homeowners as a (1) time use to evaluate your heat losses and heat gains. Mark
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05062011, 10:17 AM  #4  
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Help with daily actual output from the furnaceQuote:
I'd have to do some research for heating mode btu's and capacity but I can tell you now for cooling capacity what is needed to give you an idea CFM (450 CFM heat pump, 400 CFM non heat pump to possible 350, verifiable) x 4.5 x (enthalpy A enthalpy B) would equal actual coil capacity in btu's. Then you'd divide that capacity by the actual rated capacity of the system (so if it was a 5 ton system than five tons would be 60,000 btu's) and you'd end up with your system effective btu capacity in percentage of the nominally rated 5 tons for cooling mode. 

05062011, 11:12 AM  #5 
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Help with daily actual output from the furnace
Thanks for every input!
I saw the equation from Alliant Energy: Therm consumption estimated based on the following: Therms = (.85 X Cap X HDD X 24) / ((Ti  Td) * Eff X 100,000 Btu/Therm) Where: Cap = Furnace capacity in Btu/hr HDD = Heating Degree Days Ti = Inside temperature Td = Minimum design temperature Eff = Furnace Efficiency http://www.alliantenergy.com/UtilityServices/ForYourBusiness/EnergyExpertise/EnergySafety/010790 Does anyone know the meaning for 0.85? Thank you! 
05062011, 11:14 AM  #6 
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Help with daily actual output from the furnace
Thank you! I know the actual temps of each day from weather station. Can I do it?

05062011, 11:15 AM  #7  
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Help with daily actual output from the furnace
Thanks for your input!
I saw the equation from Alliant Energy: Therm consumption estimated based on the following: Therms = (.85 X Cap X HDD X 24) / ((Ti  Td) * Eff X 100,000 Btu/Therm) Where: Cap = Furnace capacity in Btu/hr HDD = Heating Degree Days Ti = Inside temperature Td = Minimum design temperature Eff = Furnace Efficiency http://www.alliantenergy.com/UtilityServices/ForYourBusiness/EnergyExpertise/EnergySafety/010790 Does anyone know the meaning for 0.85? Thank you! Quote:


05062011, 11:16 AM  #8  
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Help with daily actual output from the furnace
Thanks!
Quote:


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