Aquastat settings and summer water level

Wvega123

Hi we have a 100 hp boiler (see pic)

PXL_20260410_185423577.jpg

which provides steam heating and domestic hot water through a built in coil and mixing valve. My questions are as follows 1) what should the temp settings be during the heating season and non heating season? 2) should the boiler water level be raised above the coil level in the non heating system. What are the tradeoffs for alternatives.

Thanks

EdTheHeaterMan

I believe raising the water level to fully cover the tankless coil would provide a benefit.

After a closer examination of the photo of your boiler, I definitely recommend raising the water level to ensure the entire tankless coil is submerged.

The solid line indicates the appropriate water level for winter operation, when steam is required to heat the building. In some cases, this level may cover less than 50% of the coil responsible for producing your domestic hot water. that is fine when the water temperqtuer in the boiler is 215° and there is steam covering the top of the tankless coil.

By raising the water level to the dashed line in the summer when there is no steam, the entire coil becomes submerged. This increases the surface area in contact with the hot boiler water, resulting in significantly more efficient heat transfer.

That would put the water level at the top of the gauge glass or slightly above the gauge glass. You don't want to put water into the steam mains, so leave a small amount of room at the top of the boiler for air and expansion.

I do not see the water temperature controls (aquastat) in this photo. I would typically recommend setting the high limit to 180°F and the operating control to 160°F (if there are two separate controls).

If these settings do not provide sufficient domestic hot water for the building during peak demand, you can increase the operating control to 170°F or up to a maximum of 180°F. I would not recommend exceeding 180°F on the operating control. The high limit should be set approximately 10°F higher than the operating control (if you have two water temperature controls).

Wvega123

You make a good suggestion about raising the water level during the non heating season. The aquastat only shuts off the burner when it reaches the set temp then relights when it drops 10-15 degrees (the number has rubbed off but I think it's either 10 or 15).. With the recent warm weather in NYC I set it to 160 and noticed the DHW temp is in the 120-125 range which is good. I will set the aquastat to 160 and see how it goes.

I assume you are suggesting to make the aquastat to 180 in the heating season? Early in the year(and prior years) I was set to 195 and noticed the boiler was on for a shorter period during a call for heat (vs 180). I guess that's the tradeoff between 195 vs 180.