OK team, I have a recently installed Buderus GB142/45 with a max output of 141k BTUs. The house is 1,950 sq ft, 1960's construction, older windows, no basement, single floor ranch on slab, 500 sq ft over crawl space. I realize the boiler is oversized at the start, however we anticipate adding to the house at some point.
My very rough heat loss calc shows 75,000 BTUs required. There is 147 feet of baseboard which can output a max of 86k BTU with 180 degree water. I also have an indirect 45 gallon superstor tank.
Now my issue is cycling based on my zone sizes. The GB142/45 can modulate down to 42600 BTU however my zones baseboard lengths and output at 170 degrees are as follows:
Zone 1 Living Room, Playroom - 56 feet, 28k BTU
Zone 2 Front Room, 35 feet, 17.5k BTU
Zone 3 Bedrooms, 54 feet of baseboard, 26.6k BTU
As you can see, with the boilers lowest output, if just one zone calls, it will cycle with return temps too high, followed by an interval time out.
Outside of moving the boiler down in size, or doing a buffer tank, I am strongly considering combining all of the zones and running single one to drive boiler efficiency, as we literally use most of this house, most of the day (4 kids).
The baseboard is distributed evenly, so I do not anticipate any major hot or cold spots. Thoughts on a single floor zone approach? Thermostat with remote sensors for a blended average temp target on the single zone?