Sunday, December 16, 2012

Boiler Efficiency and Home Heating

This is a long post so I put a quick summary in the beginning.

Edit: I have made corrections to my initial post on Boiler Efficiency from 10/21/2012 as a misunderstanding in heating terms has resulted in invalid information. My apologies to my readers and thanks to Lou of Cromwell Energy, Inc. for pointing it out to me.  The following has been re-written entirely to account for the misunderstandings.


Our boiler was recently rated at 72% combustion efficiency.  New boilers start at 85% AFUE efficiency and high-tech units are at 91+% AFUE. Thermal efficiency does not equate to AFUE. Much older systems do not have an AFUE rating so one must be approximated in order to compare an older unit to a brand new one. Our boiler is currently running at 61.2% AFUE (est) with an output of 185,200 BTU/hr.  One must compute the heat-loss for a home to properly size a new boiler. I've computed 78,410 BTU/hr using a program called Hydronic Explorer (see below for details).  After sizing a new boiler, the pay back period is  around 7 years for a high end Buderus GB125BE/30.  There are numerous models to choose from and likewise, pricing will vary accordingly resulting in much shorter pay back periods.  An Excel file was created to adjust different installation scenarios to find the best rate of return.

Crane Sunnyday 5 Boiler Circa 1960's
Everything started on October 19, 2012, when we had a visit from our oil supplier.  We have a two year service contract included as an incentive to sign up with oil delivery from them and that day was our annual service visit.  The visit lasted roughly an hour as the technician performed the annual maintenance on the boiler.  The following were performed and noted on the receipt:

1.  Oiled Motors
2.  Oiled Circulator
3.  Cleaned Controls
4.  Cleaned Burner
5.  Cleaned Boiler
6.  Cleared Smoke Pipe
7.  Changed Nozzle
8.  Changed Oil Filter

Exhaust temperature was 540degF and the all important combustion efficiency at 72%.

Combustion efficiency is derived from a couple of temperature readings that the technician takes. The readings are taken while the boiler is running and turned into a ratio with the resultant number being a percentage.

AFUE is a more complex ratio which takes into consideration other factors.  Factors that represent a more real life efficiency.  While trying to understand the difference myself, I came across this article:  Cornell University, Home Heating Systems.  In it, the author, Mark Pierce, uses an analogy that easily allows the reader to comprehend the difference between what the technician tells you during the annual maintenance and what AFUE is.  He quotes the Consumer Guide to Home Energy Savings:

Combustion efficiency is like the miles per gallon your car gets cruising along at 55 miles per hour on the highway...(while)...AFUE is like your car mileage between fill-ups, including both highway driving and stop and-go-traffic (Wilson & Morril, 1996, p.58).

It's the AFUE rating that one sees most often when shopping for a new boiler.  But, I did not  know what the AFUE is for our boiler.  Being built in a time when such numbers weren't used, I was left searching the internet for comparisons   There were numerous articles and forums indicating that there are no equations to convert from the combustion efficiency percentage to the AFUE percentage since each is found through a different method.  However, this article from Cornell did reveal a simple equation for approximating the AFUE of an old system made before the AFUE rating became a standard number on modern units.  The equation is this:

(Combustion Efficiency) x (0.85) = AFUE est.

I am curious to know if any of my readers know their actual AFUE and have had their Combustion Efficiency revealed during a recent service.  Do the math, see if the above theory is valid.  I hope it is because the remainder of this post is based nearly entirely upon that one simple equation.  Fingers crossed...

Since I have a combustion efficiency of 72%, the estimated AFUE of my system is:

0.72 x 0.85 = 0.612 = 61.2%

My understanding of these percentages is that for every 100 gallons of oil used, 61.2 gallons are used for heating and the balance (38.8 gallons) escapes up our chimney in the form of heat and gasses.  New boilers run in the 84%+ range leading me to believe (and also from the opinion of the technician) that it is time to consider a new boiler.

First things first.  I need to have a heat loss calculation done on our home to find out what size boiler I would need.  Currently, our setup is a circa 1960 Crane Sunnyday 5 boiler with a direct water heater.  Meaning that when I turn on the hot water, the boiler turns on as if it were heating the home, yet only heating water for the faucet.  We have a single 275 gallon oil tank.  With the fuel economy from the technician,  we'll run out of oil after running the boiler for 183 hours straight.  It's important to remember that for every hot shower, regardless of how hot we make the temperature, the boiler kicks on.  When we wash the dishes, it's on, likewise, when we wash our son's soiled clothing, it's on.  After you turn off the hot water tap, the boiler still runs to replenish the hot water that is no longer in it's reserve.  The boiler's burner is much larger than a water heater's, so right there is an improvement I can make to save on oil.  As our current boiler is sized at 185,200 BTU/hr, lets see what size heating unit I need to just heat the house.

Scouring online found a free program from a manufacturer called the Slant/Fin Corporation.  They offer (or had offered) a downloadable program that will compute for you the BTU/hr heat loss of your home based on room dimensions, number of windows, what's above and below each room, etc.  It takes time to enter all the information in and you will need to do a lot of measuring to get the data for the program.  You can download the program from HERE (172 MB zip file containing the program Heat Loss Explorer 2 and two PDF files for product literature and a user guide for the program).  I only used the program for the information, disregarding the need for their product's literature.  For the Outdoor Design Temperature, I used the table from

Crane Sunnyday 5 Boiler Specifications

The numbers from the program revealed that my home's BTU/hr heat loss is:  78,410 BTU/hr.  If we were to get the same exact type of boiler, one that has a direct water heater, then our new boiler would have to be in the 128,000+ BTU/hr size range.  Big difference, isn't it?  If this program is accurate, then our Crane Sunnyday 5 Boiler is way over sized at 185,200 BTU/hr.

Lot's of information so far.  We know that our boiler is antiquated, inefficient and over sized.  I have a lot of information.  I need to put it all together and figure out what our savings would be if we replaced our antique boiler and how long it would take to return on our investment.

Savings Calculation - WARNING, MATH OVERLOAD

As of October 17, 2012, the cost per gallon of heating oil from our supplier was $3.899 (compared to regular gasoline at $4.019).  New oil boilers have an efficiency at 85% with high end models pushing just past 93%.  Lets go crazy!  I want to see what our savings would be if we got the best of the best of the best.  Worst case scenario for upfront costs.  Given our 275 gallon tank, currently:

At 61.2% AFUE:
0.612 x 275.0 Gal. = 168.3 Gallons used for heating of the 275.0 Gallons purchased.
275.0 Gal. - 168.3 Gal. = 106.7 Gallons wasted.
106.7 Gal. x 3.899 $/Gal. = $416.02 thrown out the window (well, really up the chimney).

According to, the most efficient oil-fired boiler is the Buderus GB125BE (found on on this Excel list:  It's AFUE is at 93.4%.  Very impressive compared to our meager 61.2%.

At 93.4% AFUE:
0.934 x 275.0 Gal. = 256.9 Gallons used for heating of the 275.0 Gallons purchased.
275.0 Gal. - 256.9 Gal. = 18.1 Gallons wasted.
18.1 Gal. x 3.899 $/Gal. = $70.39 wasted.

From 61.2% to 93.4%, per a full tank fill, we would save:
$416.02 - $70.39 = $345.63 per full tank!

Last winter was a gift from mother nature.  The October snow storm (seen here) was a fluke, but the following winter was quite mild compared to previous seasons (according to the locals).  We spent a little over $4,053 heating our home and using hot water from October 2011 to October 2012.

OK, so let's say that we actually did purchase a Buderus last year.  How much would we have saved assuming of course that the price of fuel did not change?

$4,053 / $3.899 Gal. = 1,039.5 estimated gallons used.
1,039.5 Gal. x 0.612 = 636.2 Gallons actually used for heating and hot water.
1,039.5 Gal. - 636.2 Gal. = 403.3 Gallons wasted.

So, with the Buderus GB125BE installed:
636.2 Gal. / 0.934 = 681.2 Gallons purchased
681.2 Gal. - 636.2 Gal. = 45.0 Gallons wasted

The difference between the two wasted amounts would equate to the savings.  So:

403.3 Gal. - 45.0 Gal. =  358.3 wasted gallon difference.
358.3 Gal. x $3.899 = $1,397.01 savings per year!

When will I make my money back?  Finding out the price of these boilers is not easy, vendors don't like to reveal the costs of labor and parts.  So, going online yet again is my only source...

Buderus GB125BE with LT-Series Water Tank 

The Buderus GB125BE has an advertised priced online from one source (I am hesitant to post the actual site since I do not know if they're a reputable source) and I know that I need at least 78,410 BTU/hr to heat our home.  If I match the exact rating, the boiler will always be running, if I go too high, it'll use more fuel than needed to heat the volume that I have.  I'll need to over size the boiler slightly.  It was recommend that the over sizing is dependent upon the township/city that one lives in.  For my area, I believe that the over size is at 30% increase for permitting.  This would equate to approximately 102,000 BTU/hr. The closest matching Buderus is model GB125BE/30 at 100,000 BTU.  It is listed costing $6,018.95.  Wow, that is quite expensive.  Plus installation, right?  And since this boiler will not be directly heating the hot water at the tap, I'll also need a comparable water tank.  Let's just assume for argument's sake that the water tank will cost around $1,200, and the installation for the two units will be around $2,000.  Together, that's:

$6,018.95 (Buderus GB125BE/30)
$1,200.00 (est. water tank)
$2,000.00 (est. labor)
$9,218.95 (holy crap!)

So, how long will it take us to make our money back?

$9,218.95 / $1,397.01 = 6.6 years = rate of return.

Basically, a 7 year period of time is needed before I would start seeing a return on my investment.

Everything I've just gone through is speculation.  Sure, this can happen, and that; one may also have a relative that's licensed that's willing to install the boiler for free.  Because of all these variables, it is quite possible that the rate of return is much shorter.  As such, I've created an Excel data sheet that I can plug in all the information and have it spit out a payback period for various different scenarios. Below is a download link for the excel file should you like to play with it.

Download Here.
(If a password login page pops up, click cancel and the file should still open)

For now, I'm still on the mends as I try to find the best price for the most efficient boiler I can find.

Due to the amount of spam comments from oil service and repair companies that this one topic has generated, I am forced to turn off all comments on this post.  Should any reader wish to contact me, please do so on the "About Us" tab at the top of the page.