New Honeywell Thermostat Impact to FHW Oil Furnace Runtime/Cycles

KC1

Hi everyone-

I have a Buderus G115WS/3 (85 MGH) oil boiler that heats 2 forced water zones and a indirect hot water heater in a 1k sq ft house. My home is very well insulated and can maintain a 60 F indoor temperature on a sunny day during the late fall (~45 F outdoor temp) with limited heating support.

A few weeks ago my RiteTemp thermostat failed so it was replaced with a Honeywell FocusPro 6000 thermostat. Unlike the RiteTemp stat which had an adjustable +/-2 swing set, the Honeywell stat has a +/- 1 fixed swing which is resulting in more frequent (once a hour or 2) but shorter (~6 minutes) heating cycles to maintain the temperature at 60 F at night degree when the outdoor temperature is ~35 F. Previously with the RiteTemp stat, the boiler would come on once every ~3 hours for ~20 minutes to maintain the temp with the +/- 2 swing.

Is this type of functionality (the shorter cycles) abnormal/a problem? Based on my reading I think the answer is "no", and that as the winter progresses (and it get colder outside), the cycles will become longer, more frequent and more energy efficient. In addition, during the winter, if I decide I want a larger swing (for better energy efficiency but less comfort) I can reduce the cycles per hour setting on the stat from 5 to 3. Right now, since the call for heat is coming on average once every few hours, changing the CPH setting wont have any impact on the cycling of the boiler.

What do you think? Is there any reason to be concerned?

Thank you for the help.
KG

Jamie Hall

That thermostat can -- and should -- be programmed for 3 cycles per hour (it's in the programming menus) for best performance on hot water heat. It comes programmed for hot air -- and that you do not want.

KC1

Thank you. I misread the owners manual--if the HVAC tech installed the stat right the cph should be (and could be) set to 3. I am away from the house for the next few days and will check the CPH on the stat when I get home.

With the above being said, given my Heating system is turning on only once every couple of hours now to maintain the temp, changing the CPH from 5 to 3 (if I need to) on the stat wont really impact the runtime/cycling of the boiler correct? The impact of change like that will only happen if there are multiple call for heat over a one hour period when it gets colder (or I increase the temperature in the house).

Thank you for the help.

HVACNUT

Looks like factory setting is 5, but you can play with it.

What aquastat or operating control is on the boiler? 2107? Hydrostat 3250 Plus? Other?

Jamie Hall

Should be 3 -- hot water. 5 is for furnaces (hot air), not boilers (hot water)

KC1

When the boiler was installed, it had a Beckett AquaSmart.  The Aquasmart control failed a few times so it was replaced with a more basic honeywell control 8 years ago.

Regarding the infrequent (once every hour or 2) and short heating cycles (6 to 10 minutes) with the new honeywell thermostat, is there reason for concern?  Even if I need to change the cph to 3, the functioning of the stat/boiler would not change under current conditions given the frequency of the call for heat is over 1 hour.

I guess I am looking for confirmation that the honeywell stat is working as intended and I need to get comfortable with the shorter, less efficient, heating cycles early in the heating season (compared to how the boiler operated with my old stat with the larger swing).

Thank you.

Jamie Hall

If it's set to 3 cph, it's doing what it's supposed to do. There really isn't any easy way to set more modern thermostats (or even most very old ones) to a larger swing.

KC1

Thank you Jamie.  Enjoy the holiday.