Best Of

You're welcome, @FirstTimeHomeOwner .

The Accel CS is a modulating condensing boiler and can modulate down to 18,000 BTU/hr.

We recommend that you zone comfort areas, so your idea of separating living areas and bedrooms is a good one, but you could leave your zones as they are if the heat uniformly. Just do not zone each bedroom separately, which would be micro zones (an exception may be a separate zone for a master bedroom with a master bath).

I am not sure if your quote includes the domestic hot water system, your heating pro would need to clarify that for you. Each Accel CS does come with controls so it is ready to add an indirect tank or plate heat exchanger and storage tank with thermal purge (which is much more efficient as the boiler finishes cold each hot water cycle vs finishing hot with an indirect tank).

Best,

Roger

@Kaos , you’re spot on about micro zoning - it will keep the boiler idling and waste energy.
But the most efficient state for a boiler is when it’s off, so the best design is thermal purge so no energy is wasted at the end of each cycle. Properly designed indirect tanks with plate heat exchangers and thermal purge will exceed the efficiency of combi boiler water heating. Last month's ASHRAE journal also had an article that highlighted why heat pump water heaters have major issues (water damage and mold in enclosed spaces of outside walls due to cold discharge air), they operate at outputs and efficiencies far below their ratings (the rooms cool off and drop performance as there is no external heat source to feed it). Further, Vermont has relatively “cheap” residential electricity ($0.225/kWh recently) compared to the rest of New England, but that’s still $6/gal propane and $9/gal fuel oil equivalent so the cost to operate the heat pump water heater is more even without including the effective impact of running a small air conditioner in your home in the winter. Most of the boiler country in the US does not have comparatively inexpensive Canadian electricity prices found in some provinces you reference.
Roger

@Kaos , the controls have to be designed to allow stratification of the tank so that continuous cold water make up feeds the plate heat exchanger. The entire system has to be designed properly or you end up with lower performance and the boiler finishes hot which wastes energy (as it does with a conventional indirect tank and combo/instantaneous systems).

Regarding heat pump water heaters, the article indicates this is a common problem that has to be solved before widespread use of heat pump water heaters. This makes sense because the rooms (and outside walls) are chilled as part of normal operation. This introduces a new mold and condensation problem in the outside walls that did not exist before the heat pump water heater was installed. The authors identified the following issues:

1. Inadequate heating capacity compared to advertised specifications.
2. Real-world efficiency significantly lower than rated efficiency.
3. Moisture-related damage and mold growth.

And believe the issues generally track back to two primary causes:

1. Insufficient access to the thermal resources inside the building.
2. Improper handling of cold exhaust air.

Roger