No heat loss calculation? No work for you!

Oct. 8, 2014
Did any of the contractors measure your home to determine the actual heat loss on a room-by-room basis? Do you have a separate water heater or do you get the domestic hot water from a coil in your existing boiler? Do you have cast iron radiators, baseboard, or convectors either recessed into the walls or mounted up against the walls? Were you able to obtain desired indoor thermostat settings last year? Over-sized boilers have lower operating efficiency and can have a shortened lifespan too  

A customer calls, asking me for advice.

She says, “I just spoke with a very nice woman in your office. We are trying to get a new hot water boiler. We have had three contractors out to give us bids. The quotes range from $5,800 to more than $11,000. I have been researching the boilers online and have read negative feedback on some of them. I found your company on www.heatinghelp.com.

“Our house is a two story colonial (2500-sq.ft.). I received quotes for a Peerless oil fired cast iron boiler, a Columbia steel boiler, a Burnham (PV8H3) cast iron boiler, and a Weil McLain boiler. It is hard to know who to trust and which boiler is the best.

“Our service company told me that we need a new boiler when they came in August to perform the annual maintenance. They also suggested a new one last year and several years ago when the economy tanked. Last October we paid $585 to re-pipe the relief valve to code, replace oil filter, and replace leaking mixing valve although they suggested we get a new boiler instead.

“If you have any advice, I would appreciate it.”

First I ask her, “Did any of the contractors measure your home to determine the actual heat loss on a room-by-room basis? If not, they are accepting your existing boiler's output rating at face value.”

“No, however, one out of three contractors measured all of the baseboards in each room.” 

My next question is, “Do you have a separate water heater or do you get the domestic hot water from a coil in your existing boiler?”

“We get our hot water from the coil in the existing boiler.”

I ask, “Do you have access to natural gas?”

“No.”

“Do you have cast iron radiators, baseboard (copper tubes with aluminum fins behind the cover), or convectors (a cabinet, typically 24" tall) either recessed into the walls or mounted up against the walls?”

“We have baseboards.”

“Were you able to obtain desired indoor thermostat settings last year? If so, do you recall hearing the boiler turn On/Off and approximately how long it was Off between On cycles during the coldest weather?”

“We were able to maintain desired heat settings last year. We were warm and only used 667 gallons of oil, which is low. The year before we used 703. I don't really remember the time between On and Off.”

“Why are you interested in replacing the existing boiler? Worn out or due to high fuel costs?”

“We purchased this boiler 16 years ago in an emergency situation in the middle of winter. Apparently bolts on coil were not tightened by a previous oil company during the first three years so there is leaking and corrosion. Also, some of copper pipes are leaking.”

“Sixteen is relatively young for a good-quality cast iron boiler. From your description, it sounds like the only real issue is the leaking at the coil/plate area along with the corroded copper water lines. If true, you have options available to avoid the cost for a new boiler if your existing boiler is close to being correctly sized. I don't know how old your home may be, but I often find the owners, or previous owners, have upgraded things like insulation in the attic, new more efficient windows and/or doors. Changes in the building envelope virtually ensure the existing boiler will be over-sized and the odds are good that it was over-sized from Day-1.” 

“I am not sure if our boiler is the right size. We put all brand new windows, doors, garage doors, vinyl siding, and new roof on our house under 10 years ago.”

“Those changes alone ensure it is over-sized. Over-sized boilers have lower operating efficiency and can have a shortened lifespan too. Given that the boiler is over-sized, you'll be ahead of the game by installing a new right-sized boiler. Pay close attention to the stated operating efficiency. A few percentage points will make a long-term financial difference. Most important, however, is which brand does the chosen contractor feel is your best buy because that will most often be the brand providing the best support to them for parts and technical service.”

Repeating history

First and foremost: absent a thorough heat loss calculation done on a room-by room basis, the contractors are simply repeating history. The one who measured the baseboards has done what's commonly called a connected-load survey. That's assuming they measured just the finned/tube lengths and not the total length of the enclosure.

I rarely meet a correctly sized boiler or baseboard system. The heat loss calculation (I use Manual-J, which is universally recognized and accepted by all authorities having jurisdiction in the U.S.) tells me how many Btus per hour are needed on the coldest day of the year. I then cross-reference that to the rated output of active (tube with fins) baseboard output per lineal foot, which indicates how hot the water needs to be to meet the heat loss on that coldest day. As a general rule, for every 3°F I can lower the existing water temperature (likely set for 180°F /160°F = 170°F average), your energy consumption drops by 1%.

If I add outdoor reset to the boiler, you can add another 10% to 30% reduction in fuel usage. If your new boiler is a heat-on-demand-only appliance, that will eliminate most of the stand-by heat loss: boilers are not well insulated and have relatively high stand-by heat losses.

Consider options

You should consider some options for DHW (domestic hot water).

  • Least expensive up-front cost is an electric water heater, but costs more to operate than other methods.
  • Depending on space (cubic foot air volume of free air space - min of 800-cubic-feet), a heat pump water heater will be the least expensive method for heating DHW. Rebates may be available from your utility provider, which can make this a very attractive option.
  • An indirect water heater can be added and "seen" by the boiler as just another heating zone. The boiler would run only when the indirect tank's sensor indicates it needs thermal energy. The boiler would no longer sit there maintaining 180°F, or hotter, water temps 24/7/365. Conserves energy. 
  • You have three zones (three zone valves and one 87-watt-power-consumption circulator) and there is significant energy conservation available by utilizing an ECM (electrically commutated motor) circulator that would use a fraction of the current electrical consumption. (see video link)

Step No. 1: Heat loss calculation on a room-by-room basis. Absolutely required!

Step No. 2: Compare each room's heat loss to the active baseboard to determine actual hottest water required. Absolutely required if you want to conserve energy!

Step No. 3: If a new boiler is chosen, incorporate outdoor reset. Must do #'s 1 & 2 to know where to set the outdoor reset curve, which will lower the boiler's upper limit as outdoor air temperatures rise.

Step No. 4: Avoid the use of an internal coil and decide which DHW alternative option is best for your application.

Step No. 5: If you keep your existing boiler, disable and repair the leaks, turn this into a heat-on-demand-only appliance, and go back to No. 4.

The final results can be fairly dramatic. The home in this video, www.youtube.com/watch?v=Yz5yiFwPh1k, saw more than a 70% reduction in fuel usage.

All Dave Yates material in print and on Contractor's Website is protected by Copyright 2014. Any reuse of this material (print or electronic) must first have the expressed written permission of Dave Yates and Contractor magazine. Please contact via email at: [email protected].  

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