HX condensation at outlet temp of 155?

Dave_61

I had written earlier about my vastly oversized Lochinvar boiler (300 K BTU). It has a 2 stage gas burner, so I simply shut off the second stage (something that Lochinvar said I could do).
We have a total of 5 zones (3 fan coils, a small radiant loop under wood subfloor, and Phase III indirect).
Currently, with 150K BTU burner running, and the water temp set at 180 for fan coils, I went to look at the boiler this AM as the outdoor temp was 9 deg F.
The house was very comfortable. All three fan coils were calling for heat, and the temp gauge on the boiler outlet was reading about 150-155 degrees. Is this situation OK? I currently don't have a way of measuring inlet temp. As long as the water temp leaving the boiler is greater than 150, does that mean there is no condensing of flue gasses? Is there any way to see if condensing is occurring?
We have a clear vinyl tube attached to the vent pipe that exits the side wall of the house, and there is no water in it presently.
Thanks
Dave

Rich Lowenstein

Condensation depends on return water temperature, but in any case it is not an on-off switch...as the water gets hotter, there is less condensation.

I am assuming this is a NON-condensing boiler and you are worried about condensation harming it? If so, 155F output is not too bad. Of course it would be better if the temperature went higher. But you are only reporting one reading; did the water get hotter with time? Only the maximum temperature is relevant.

If it won't go higher than 155F, this means that 155F water is hot enough to deliver the entire 150KBTU to the house. This is a problem encountered when you have excess radiation but you haven't oversized the boiler. If you turn on the second stage, the water will get to 180F easily, but then the thermostat will make it cycle much more often. If you are worried about short-cycling due to oversizing, but also worried about condensation, you need a bypass to increase the water temperature seen by the boiler. Or you could just leave the second stage on.

If it is not a condensing boiler, there is no condensate drain. Any condensate that is not burned off at the maximum temperature will sit there and slowly eat through the HX.

Boilerpro_3

Also depends upon combustion efficiency

The closer the boiler is operating to perfect combustion efficiency, the higher the temperature the boiler will condense at. If you are running at 50% gas input, but still are getting the majority of your full fire combustion air running through the boiler, 155F is probably OK. However, if you are running 155F water outlet at full fire, you probably will have condensation in the boiler. Copper tube boilers seem to be especially sensitive to return temp, due to the lack of mixing in the heat exchanger.

Boilerpro