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Old 05-05-2011, 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: G20Q3/4E-100-3
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!

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Old 05-06-2011, 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.

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Old 05-06-2011, 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 where-by 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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Old 05-06-2011, 10:17 AM   #4
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Help with daily actual output from the furnace


Quote:
Originally Posted by Amy28 View Post
Hello Sir,

I have very old Gas furnace:
LENNOX gas furnace
Model: G20Q3/4E-100-3
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!
Your system capacity SHOULD be 100,000 btu's per hour. If you are getting it is an entirely different situation.

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.
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Old 05-06-2011, 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!
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Old 05-06-2011, 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?

Quote:
Originally Posted by beenthere View Post
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.
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Old 05-06-2011, 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:
Originally Posted by Doc Holliday View Post
Your system capacity SHOULD be 100,000 btu's per hour. If you are getting it is an entirely different situation.

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.
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Old 05-06-2011, 11:16 AM   #8
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Help with daily actual output from the furnace


Thanks!
Quote:
Originally Posted by Jackofall1 View Post
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 where-by 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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