Slam dunk a two point energy swish

Feb. 1, 2009
As the homeowners add other improvements to cut energy losses in coming years, the Modcon will simply adapt to the newly-reduced heat-loss, and fuel consumption will be further reduced.

Imagine you live in a home with no insulation, single-pane glass windows and solid wood doors: the kind of home many inner-city and country folk live in that was built prior to 1960. Your fuel bills have been keeping you in the poor house - literally. You're aware that you could be upgrading your home's energy envelope and reducing energy lost by adding insulation in the attic, and installing new windows and new doors - the low-hanging fruit on the energy-loss tree. But is that the best first investment you can make when putting your home on an energy diet, or would a new heating system be the wiser place to begin?

Your imaginary house is a two-story, 2,500-sq.ft. home with single-pane clear-glass wood frame windows that makeup 20% of the walls' square-footage, including two 21-sq.ft. exterior solid-wood doors. It's an older home, so we'll set the infiltration in our RHVAC Elite Software program to “poor.” The home will be in SEPA with design-day temperature set for 10°F. Heat loss equals 162,611 Btus per hour. Natural gas prices per Ccf (100 cubic ft.) were $1.80 the previous year, but are now $2.34 - your 12-month budget plan went from $542 to $704. You've got to do something to cut those costs, other than setting the thermostat to sub-arctic discomfort levels below last winter's 65°F indoor chill. You're ready to call in the contractors. You have budgeted $12,000 to spend on upgrades for your home.

So begins the parade of contractors. Ironically, every one of them will take the time to do a heat loss/gain calculation and project how much you will reduce energy consumption. (I also believe in Santa, the Easter Bunny and the Tooth Fairy!) First up are the insulation, window and door contractors who each do their best to sell you on the notion that their products will give you the best bang for your buck. The attic insulator's report shows a drop in heat loss to 115,315 Btus. If you hire them to install R-19 fiberglass batts, and if you toss in new windows and doors, your adjusted heat-loss total will be 92,653 Btus. The gas company representative calculated that your new monthly budget bill would be lowered to $401. Your $12K budget will be depleted if you go this route.

The mechanical contractors come next. You're getting two separate opinions regarding efficiency upgrades based on the 78% rated model you have: atmospheric chimney-vented appliances are rated at 84%; and Modcon (modulating condensing) appliances are rated at 98%. You've told them the equipment must be sized for the home as it is and that any other upgrades will come at a later date, if and when you can afford them.

The atmospheric chimney-vented appliance's up-front cost is very appealing, in spite of its lower efficiency rating, and you'll need to save for just two more years until you can add that attic insulation. Doors and windows will have to wait. Your monthly budget for heating, however, is projected to be $654.

The 98% efficiency rated Modcon will, you've been told, adapt to your home's heat loss by modulating its input/output to match the heat loss at any given moment in time. In spite of there being just a 20% difference in listed efficiency-ratings, this contractor is telling you that your fuel usage will be cut by 40% or more, and proof-positive is being provided with references and documented cases. If true, your monthly fuel budget plan will be $422.

Ding-ding-ding - we have a winner! The Modcon is the best choice. Why is this? After all, the other upgrades were projected to cut monthly budget payments ever further - an additional $21 per month. Here's the deal: a heating appliance is only going to be 78% efficient at design conditions and that's assuming it was sized correctly in the first place. Oversized equipment short-cycles lower operating efficiency, and by adding the insulation, windows and doors, the appliance is guaranteed to be grossly undersized. Here's the clincher: as outdoor temperatures modulate, actual efficiency for on/off heating appliances suffers and can be as low as 45%. So, even though the fuel usage will be lower, so too will the efficiency and a new issue will rear its ugly head - sustained flue gas condensation, which will rot out the heat exchanger and damage that old unlined brick chimney. The potential for carbon monoxide issues loom larger. A Modcon appliance does just the opposite: as outdoor weather moderates, the efficiency gets better or remains the same.

As the homeowners add other improvements to cut energy losses in coming years, the Modcon will simply adapt to the newly-reduced heat-loss, and fuel consumption will be further reduced. Does this sound far fetched?

Here's a documented case from our files regarding an 82% rated efficiency heating plan using 7,800-Ccf per year (on average). In 2002, cost was $3,900 at 50 cents per Ccf, and in 2003 cost was $5,850 at 75 cents per Ccf. A 95% rated efficiency Modcon was installed, in 2004, to add more heating since the great room was too cold. After the installation, the cost was $3,300 at 75 cents per Ccf (4,400-Ccf had a 43.6% reduction in spite of the 13% listed efficiency rating difference) for 2004 and 2005. Metal-framed single-pane windows were replaced and insulation added to cut heat losses in 2006. After these two updates were made, the cost was $3,000 at $1.25 per Ccf (2,400-Ccf had a 45.5% reduction) in 2006 and 2007. The overall, total reduction in fuel consumption with no change in lifestyle equaled 69%. Nothing but net!

Dave Yates owns F.W. Behler, a contracting company in York, Pa. He can be reached by phone at 717/843-4920 or by e-mail at [email protected].

All Dave Yates material on this website is protected by Copyright 2008. Any reuse of this material (print or electronic) must first have the expressed written permission of Dave Yates. Please contact via email at: [email protected]

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Dave Yates

Dave Yates material in print and on Contractor’s Website is protected by Copyright 2017. Any reuse of this material (print or electronic) must first have the expressed written permission of Dave Yates and Contractor magazine.

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