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Is your modulating boiler properly sized?

November 14, 2014

Modern boilers gain 5 to 10% increases in efficiency versus their traditional “on-off” counterparts by being able to adjust their output to meet the demand.  “On-off” boilers are either on at full-fire or they are off.  Modulating boilers can operate at anywhere from 20% of 100% of their full fire capacity.

By operating at lower fire, the boilers gain efficiency and cycle less.  To maximize this performance, and minimize boiler cycling, which is a drag on efficiency, the boiler must be properly sized.  In the past, it was common for boilers to be sized up to 50% greater than their “coldest day” demand.  This further increased boiler cycling.

Prestige Condensing BoilerWhen replacing an old boiler or installing a new one, it is worth the time to perform a proper heating load analysis.  This will help avoid paying for a boiler that is bigger than needed, or installing a boiler that cannot meet your heating needs.  If a larger boiler is installed than needed you will overspend not only on the initial cost of the boiler, but also by extra fuel cost due to the less efficient operation due to boiler cycling.  While a modulating boiler will operate longer and cycle less than an “on-off” boiler, it still will cycle when the load is lower than the minimum output of the boiler.  Therefore, an oversized boiler should be avoided.

While it may seem logical to simply size your replacement boiler based on the one that is being replaced, a heating load analysis can better determine the size required.  Even if the original boiler had been properly sized when it was installed, there probably have been significant improvements to the house since then.  It is very common for extra insulation and more energy efficient doors and windows to have been installed.  All of these will impact the heating load.

Triangle Tube’s Prestige and Challenger boilers are able to modulate down to between 25% and 30% of the boiler’s maximum output.   This helps improve efficiency especially during the warmer days in the heating season.  This modulation is also helpful when using an indirect water heater like Triangle Tube’s Smart series.  Make your radiant heating system as green as possible by properly sizing your boiler.  Contact us today for more information.


Jim Lavallee Plumbing
Serving Eastern Massachusetts and the Boston area
Phone: Toll-free (888) 884-4122



(original article)

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