3 ms·

>but I'm not buying it if I find out it won't work with a dry contact input. But... why?

sokoloff 4y ago
Because it's from a new entrant to the market and I don't know that their complex interface will be available, supported, and serviceable 12 years into the 20 year lifetime of the equipment. I do know that I will always be able to provide a dry contact closure in the event they go belly-up and the thermostat goes unsupported. I have my current gas boiler working via an outdoor reset mechanism that provides flow water at 116°F to 135°F via a dry contact closure from the zone relay box. There's no reason for me to believe that Bosch (and others) can create a modulating boiler that works efficiently from just a dry contact closure input from the house (plus a flow temp sensor, a return temp sensor, an outdoor temp sensor, and a programmed reset curve in the heating unit), but that a heat pump would be unable to do the same. The boiler can modulate up and down based on the delta-T between return and supply and the target supply temp from the outdoor reset. A heat pump could do exactly the same thing (with an inverter drive, it can do it with even more granularity than a multi-stage gas valve affords).
- dtgriscom 4y ago
  Ah, clarification: you're OK with using a proprietary (and intelligently proportional) thermostat, as long as there's a backup dry contact option if the factory thermostat fails and is irreplaceable.
  - sokoloff 4y ago
    Yes, that’s true; I’m ok to use a proprietary thermostat if I think it will save me money in 2 years max. (I’m using Sensi wifi thermostats that will become non-programmable if they stop supporting their phone app. It’s ok, as they were around $40 each after incentives and I’ll save most of that just this heating season. Its interface to the boiler is just power, common, and call-for-heat.) At least in a hydronic (air-to-water or gas-fired) application, an intelligent stat is not mandatory to get decent efficiency (from variable control). You still have building heat transfer rate and outdoor temp sensing available inside the unit even with just a contact closure.

Because it's from a new entrant to the market and I don't know that their complex interface will be available, supported, and serviceable 12 years into the 20 year lifetime of the equipment. I do know that I will always be able to provide a dry contact closure in the event they go belly-up and the thermostat goes unsupported. I have my current gas boiler working via an outdoor reset mechanism that provides flow water at 116°F to 135°F via a dry contact closure from the zone relay box. There's no reason for me to believe that Bosch (and others) can create a modulating boiler that works efficiently from just a dry contact closure input from the house (plus a flow temp sensor, a return temp sensor, an outdoor temp sensor, and a programmed reset curve in the heating unit), but that a heat pump would be unable to do the same. The boiler can modulate up and down based on the delta-T between return and supply and the target supply temp from the outdoor reset. A heat pump could do exactly the same thing (with an inverter drive, it can do it with even more granularity than a multi-stage gas valve affords).

dtgriscom 4y ago
Ah, clarification: you're OK with using a proprietary (and intelligently proportional) thermostat, as long as there's a backup dry contact option if the factory thermostat fails and is irreplaceable.
- sokoloff 4y ago
  Yes, that’s true; I’m ok to use a proprietary thermostat if I think it will save me money in 2 years max. (I’m using Sensi wifi thermostats that will become non-programmable if they stop supporting their phone app. It’s ok, as they were around $40 each after incentives and I’ll save most of that just this heating season. Its interface to the boiler is just power, common, and call-for-heat.) At least in a hydronic (air-to-water or gas-fired) application, an intelligent stat is not mandatory to get decent efficiency (from variable control). You still have building heat transfer rate and outdoor temp sensing available inside the unit even with just a contact closure.