Contractormag 2219 Mathalgebra

Contractor businesses profit from mathematics

Feb. 6, 2015
There’s money for you in math! It literally takes longer to take the measurements than it does to run a computer-based Manual-J calculation. Like any computer program GI = GO (garbage in = garbage out), so training is advised!
Photo: iStock/Thinkstock.

I hated math in public high school. Being dyslexic presented numerous opportunities to reverse numbers and the red checkmarks and notes stating “Can do better” or “Doesn’t apply himself” only added to my aversion from all things related to mathematics!

A career in the trades led to night school where math once again reared its ugly head. However, this time the math had real meaning and led to resolving real-world problems. Over time, math also led to higher profits.

More than three decades ago, I provided a quote for a large private residence to replace an aging 1,350,000-Btuh boiler. An elderly woman lived in the 6,500-sq.ft. home constructed in the late 1800s. That’s almost 208-Btuh per square foot: not even if they threw open the windows and left all the doors ajar! At the time, I was convinced her boiler was oversized. The mere mention of reducing the Btu-size convinced her I was trying to rip her off. Funny how some visits, like hers, stick in the memory banks. She sent me packing.

Two years ago, a return visit found the once stately mansion had been converted to apartments. The new landlords were more interested in cosmetics and remodeling, which included new kitchens and baths (no complaints here), than in doing anything with the beast in the basement in spite of my urging them to consider its replacement with a high-efficiency boiler or boilers (for redundancy).

Then, a few months ago, one of the twinned water heaters developed a pinhole in its flue-tube and needed to be replaced. Why not do both since the pending regulation changes in April 2015,, will spike costs? And that’s when the landlords began lamenting how much the home was costing them for DHW and heating. Last year’s Polar Vortex got their attention and drained their wallets: $10,000 for natural gas! “Is there anything we can do to reduce our costs? How long will it take to get a return on the investment?”

There’s money for you in math! It literally takes longer to take the measurements than it does to run a computer-based Manual-J calculation. However, like any computer program GI = GO (garbage in = garbage out), so training is advised. Go to to test drive this course for free.

I have reviewed Manual-J calculations that were seriously flawed that, unfortunately, resulted in grossly over- or under-sized equipment being installed or, worse yet, ended up resulting in expensive lawsuits. The Manual-J calculation revealed the actual heat loss on a design-day (coldest day) for this 6,500-sq.ft. apartment building was under 250,000-Btuh! That’s one heck of a reduction from 1,350,000-Btuh and not the first time a heat loss or heat gain calculation gave me serious pause for thought. A difference that large meant I would review my inputs.

What if my inputs turned out to be garbage? No one to blame but me if that turned out to be true. Fortunately, there was an easy way to cross-check the heat loss calculation: a connected load survey! Truth be told, this was a necessary step to take in order to be able to define what water temperature would be required on a design day, so that I could determine exactly where to target the upper water temperature limit for the outdoor reset curve. The connected load for the home’s standing cast iron radiators revealed the heat-loss calculation was spot-on.

Standing cast iron radiators make wonderful companions for outdoor reset. The room-by-room heat loss can then be divided by the square feet of equivalent direct radiation (EDR) of each radiator. Once you know the Btuh required per square foot EDR, you compare that to the Btuh output at various water temperatures until you meet or exceed the required output to meet the room’s heat loss on design-day conditions.

For example: a room has a 13,919-Btuh-heat-loss on a design-day of 13F (ASHRAE guideline for my area). The radiators in this room have a 140-sq.ft EDR. At 170°F average water temperature (boiler set to run 180/160°F), each square-foot gives off 150-Btuh. 140 x 150 = 21,000-Btuh. 13,919/140 = 99.42-Btuh per square-foot required on that 13°F day. I can lower the water temperature to 145°F and that’s the hottest water needed on the coldest day. The outdoor reset curve can be adjusted to carve out the maximum energy conservation value (ECV) and provide the owners with an excellent return on investment.

I’d love to share this easy to do math with you — for free! Follow this link from the Radiant Professionals Alliance (RPA) website:

Naturally, the landlords had sought out two other bids. I would too, given the dollar amount for the job. Both of our competitors simply took their direction from the tag on the boiler. A few hours invested in doing the math enabled both the customer and us to profit handsomely.  

All Dave Yates material in print and on Contractor's Website is protected by Copyright 2015. Any reuse of this material (print or electronic) must first have the expressed written permission of Dave Yates and Contractor magazine. Please contact via e-mail at: [email protected].      

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