Hey all,
I just recently did an energy audit and the customer told me that he is burning approximately 8gals. of fuel oil a day.  Im looking for a formula to compute a ball park estimate of how much fuel oil should be consumed per day.  I know it has to have something to do with heating degree days, insulation type, btu output of the furnace, sq ft of the home.  I just dont know how to calculate it.  Or what formula to use.  I have googled it and found nothing, and I have looked through my Residential Energy text book by John Krigger and it mentions nothing of the sort.  There has to be a formula.  If you all can help me out here Id greatly appreciate it!  I look forward to your advice as always its a pleasure to read!  Hope all is well with everyone!

 

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Dave Price
Level I IR
J&D Thermography
Peru, NY
david.o.price@gmail.com
(518)335-9474

It is NOT a single, simple formula. Basically you must look at load of each section of the building and the efficiency of the system delivering the energy. Rob has done a webinar overview on this topic. I thought Kirigger's book address this in principal. There are websites that might get you in the ballpark but please appreciate this is not as simple as you think. Try <<http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm>>.

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Thermally Yours,

John
ASNT NDT Level III #48166
The Snell Group
www.thesnellgroup.com
www.thermalsolutions.org
800-636-9820

John,
The book addresses home heating loss, the costs of ventilation and R Values and the sort.  What I was looking for formula or calculator that can give me an accurate ball park figure for the typical fuel use of a 4100sq ft home.  I just think 8 gallons a day is a heck of a lot of fuel.  I talked to a local HVAC tech and they said that they make slide rules and stuff for this sort of deal.  I was hoping some one knew the actual formula or calculations so I could note them and know the basic theory behind it before I start using the easy route of a slide rule or something.  I hope that clearifies it maybe.

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Dave Price
Level I IR
J&D Thermography
Peru, NY
david.o.price@gmail.com
(518)335-9474

Hi Dave,  1st question is how do they know it is 8 gal./day? Is that the amount used last year divided by 365? or is that based on how many gallons they used since their last fill up? There can be a big difference! How cold has it been? Is it a boiler or furnace? Does the fuel oil also heat domestic hot water?  How big is the house?

What you are looking for is a Heat Loss Calculation. You have to multiply the square footage of the walls, floor, roof and windows by the respective U value (1/R). Multiply that total by Heating Degree Days (HDD) for the period (typically a year) to find the total BTUs needed to heat the house to 65 degrees. That would have to be adjusted for how warm they keep the thermostat at. Then you have to factor in the efficiency of the heating system and the natural air infiltration rate.

What is probably more useful to you is to use is the Home Heating Index (HHI), which is:   (BTUs used in a year for heat) / (sq.ft. of heated space) / (HDD)  and compare that to a HHI chart. A very energy efficient home will have an HHI of 2-4, the average home is around 10-12 and a very inefficient home with little insulation and inefficient heating system will be 20+.  (#2 fuel oil has about 138,000 BTU/gal.)

 

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Brad Cook
Building Performance Services LLC
BPI Accredited
Warren, Vermont
Level I Thermographer
"Always look at the WHOLE picture"
"The more you look, the more you see"
"You can never take enough pictures"

Brad,
The home is 4100sq ft, built in the 1840's.  It has the lathe and plaster and dead air for insulation.  He has 2 100 gallon fuel tanks in the basement and he says every 25 to 28 days he has had them filled.  Im not sure where Warren Vermont is, but we live up in the northern tier of NY right across the lake from Burlington, so we did have a really cold snap last month, and otherwise its been a very seasonable winter.  I have both those formulas that mentioned above thank you.  I will have to use those I guess. Thank you for your help, much appreciated!

 

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Dave Price
Level I IR
J&D Thermography
Peru, NY
david.o.price@gmail.com
(518)335-9474

David,

I also perform energy audits for customers. Because of lifestyle it is difficult to say what each individual home will or should use. By comparing them to other homes you also risk alienating the customer. In some cases the customer can become defensive and at that point nobody wins.

 You can have two units and identical houses in every way side by side and the usage will always be different and sometimes by a large degree. This is based on lifestyle choice that the occupants make.

The heat load formulas are for designing mechanical units in different areas based on square footage and climate among other things. Lifestyle is not addressed.

I prefer the method of taking each house as an individual unit. I compare the current condition to the recommended condition. I use the data from testing and software to determine this. I provide a rough estimate of cost of upgrades and their expected performance.

By using this method I take the lifestyle out of the discussion but include it in the formula. I am modeling their home on two different levels. I tend to stay away from comparing them to their neighbors.

Glen Gallo

glen@rede3.com

Glen,
That is also what I am trying to do.  The customer seemed very upset that his home is burning approx. 8gal/day.  I was just trying to figure out about how much a typical 4100 sq ft home would use in a day.  I have been in contact with this customer over the past few days in regards to this.  I have also talked to an HVAC technician about this.  He said it does sound about right.  The customer is looking for a decent cost effective fix.  Unfortunately Im not sure there really is one seeing that his exterior walls are made from the lathe and plaster with dead air space for insulation.  Besides from air infiltration along the joints and corners the whole wall itself seems to be about 7-10 degrees cooler.  I have talked to a few friends who are contractors and they said to rip all that out and retrofit with either a cellulose, foam or nu-wool type insulation would be very costly for a home of that size.  Its hard to tell the customer things like that, becuase if they are anything like me and hear that they will be kind of upset that they are living in a home that is going to be very costly either way they go.  Thank you for your input Glen, I welcome any other comments as well!

 

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Dave Price
Level I IR
J&D Thermography
Peru, NY
david.o.price@gmail.com
(518)335-9474

Back in the late 80's my parents had their old farm house insulated. They hired someone who came in and put about 500 1inch holes through the siding and filled the wall space with some sort of insulation through those holes and capped them.

Dave: There are many different ways to estimate this - but it is complex.  There are many factors that you need to look at to determine what you are asking.  For example, where is the thermostat located, the wind speed outside, convection sources inside, temperature wanted inside, outdoor temperature, insulation value of walls, ceiling, efficiency of furnace, etc...

 I estimate this within industrial facilities.  Good engineering practice uses good estimates for many of these factors because not all factors can be measured effectively for what you are asking.  But, you can find wind speed and outdoor temperature from weather data.  You can measure combustion efficiency of your furnace.  You can obtain R-values of your insulation and walls from literature. ETC...

 So, you probably can come up with a good estimate for how many Btu's are lost based on these factors.  Also, do not forget infiltration/exfiltration, something that is often forgotten.  A good tight building/room typically has an air change per hour of 0.1 to 0.3.  An average room is about 0.5.  A leaky room has 1 or more.

Bill,
Thank you for the information.  I ended up talking to an HVAC technician and he helped me through it.  Thanks for all the help!

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Dave Price
Level I IR
J&D Thermography
Peru, NY
david.o.price@gmail.com
(518)335-9474