Do you need a more efficient (and expensive) modulating condensing boiler if you have baseboards?

That was the question posed in a discussion group I follow, and many contractors said, “No, a cheaper, conventional boiler is just fine.” The baseboards require high temps of 180° at all times, they said, and condensing boilers save fuel by heating at low temperatures. Plus, baseboards respond too slowly to the outside-reset feature of condensing boilers.

I respectfully disagree. Condensing boilers can result in significant energy savings when used with baseboards.

First off, there is a good part of the heating season where you don’t need those high temps – such as the “shoulder” months of October and March, for instance.

Secondly, systems using conventional boilers tend to be over-sized, and huff and puff more heat up the chimney than is used.

Consider this, a 30° reduction in water temperature will pencil out to a 10% fuel savings. In the shoulder months, you may run your baseboards at 130°, while in colder seasons, you may run the baseboards at 160°. So, running your baseboards at 130° would save you 18% over the high temps of a conventional boiler. When you consider that a condensing modulating boiler runs at 95% efficiency, while a conventional boiler is at 80% or so efficient, you’re adding that 18% savings on top of your already higher efficiency rating.

Thirdly, you absolutely need a good reset control. Contractors put reset controls on old-style set-temperature boilers all the time, but their effectiveness is limited. Condensing modulating boilers do it now. Some do a crummy job with poor control, and some are very sensitive and dead on for comfort at the lowest operating temperature possible (and energy savings).

I watch my new HTP Elite Plus with gas adaptive technology all the time. I can see exactly how my house is performing. I retrofitted with underfloor plates in the 1/3rd basement that I have and low-temp (Heating Edge) baseboards in the rest of the home. Not to get too carried away with my details, but I found that my basement stayed warm just from the staple-up for the upper floor.

As an experiment, later in the next heating season I installed low-temp baseboards in the basement. My condensing boiler adjusted the temp down about 8° overall compared with the previous year’s operating conditions. I have my program set from 110° to 140° with an 11° swing. It follows outside temp and sets the water temp to about 123° on average.

When a T stat comes on after being off for a while, the boiler control measures the Delta T in the zone in accord with the outside temperature. If it is below 16° outside and the zone fluid temp has a Delta T difference of 11°, the boiler will ramp to max setting of 140° until the Delta T narrows, which doesn’t take long. It does that so that the zone doesn’t have an under-swing because of the off/on setting of the T stat.

So, to recap, baseboards love modulating, condensing boilers – and we love the accompanying energy savings.