Propane Boiler

[Scott McNab]

Thanks in advance for any help. I recently had a propane boiler installed. Just trying to figure everything out and get the right settings. A little background. The circulation pump is controlled by the house thermostat and the boiler is controlled by a low limit aquastat. What temperature should I set the low limit and the differential (5 degrees to 30 degrees). Seems like a waste of propane this time of year keeping the water hot when the home doesn't call for heat that often. Daytime highs are around 7 degrees. Would an outdoor reset control be worth the money? The boiler is only used for home heating as I have a separate electric water heater. Just seems like it runs quite a bit. I'm used to an oil Boiler so maybe I'm overthinking things.

 

[Dana]

Little hints such as the model name & number of the boiler might be useful here.

Other useful things to consider would be how much radiation (per zone, if zoned), the heat load at the 99% outside design temp, etc.

With a postal code and some exact oil fill up dates & quantities it would be possible to infer the 99% heat load from wintertime fuel use & heating degree-day weather data,which would at least be a place to start.

In general a bigger differential results in longer more efficient burns, but the entering water temperature at a cast iron or steel boiler shouldn't be allowed to chronically run at temperatures below 130F/55C lest the exhaust condensing on the heat exchangers can ruin it in one heating season. Finned water tube boilers are more tolerant of cool return temps, so it matters what you actually have. Most cast iron propane boilers are cold-startable without damage, but the controls would have to be re-configured,to cold start and inhibit the circulator until the boiler had reached a reasonable temperature. and it introduces a delay from the initial call for heat as the boiler heats up, but that's usually not a big deal if the boiler is sized reasonably for the heat load (which sometimes happens, despite the common impulse of installers toward ludicrous oversizing factors.)