hot water heating for a small duplex

JAtch_2

We own and rent a small, older, duplex in central Vermont and are evaluating the alternatives for replacing the two electric domestic hot water (dhw) heaters that serve the building. Any thoughts or comments will be greatly appreciated as there seems no clear best scheme in this situation.

The basic info for the current set up:
unit1= 1370sq.ft, 2 baths with showers, both with 1.5gal shower heads. 50Gal electric dhw heater (vaughn stone lined), oil forced hot air furnace ,about 5 years old, chimney vented, with it's own oil tank.

unit2= 975sq.ft, 1 bath with shower, 1.5gal shower head. 80Gal electric dhw heater (monthly rental), oil forced hot air furnace, about 25 years old, chimney vented, with it's own oil tank.

Our basic plan is to switch the dhw for both units to a single oil powered device and meter each unit's utilization with flow meters, one oil and water devices for each unit and the washer.

Other basic info: 1st, either or both chimneys will need to be lined to handle another device being vented up them; 2nd, the building's location limits the possibilities for direct venting although with a run of perhaps 30 feet it might be able to be done on one side of the building. Finally, we want to continue to use oil as the primary heating fuel.
Eventually we want would like to move 1 or both units fully to hot water heating but, without the lottery win, that will need to be done a step at a time.

Working with our heating contractor, we have come up with
three alternatives, one which seems too costly for now and two variations of an oil dhw setup.

The best but most costly alternative seems to be to switchover the smaller apartment to hot water heating and use a indirect tank to provide dhw for both units. The heating contractor's installation estimate for a basic baseboard heating set up for the unit is $8000, and adding in a boiler, chimney liner and btu metering we assume would add another $4000 to the cost. We also estimated a variation of this scheme with an air handler but have basically rejected that as we don't have much faith in the old ductwork.

The 2nd alternative is a toyotomi om148 oil water heater to serve both units, chimney vented with the existing oil furnace. Our primary concern with this alternative would be whether the toyotomi would have the capacity to serve both units, so for insurance this would be piped to optionally use the existing 50Gal vaughn electric heater as a storage tank if the toyotomi capacity seemed in adequate. We hope the storage tank would not be used at all to avoid standby losses. Rough cost estimate, $3000.

The 3rd alternative would be a similar setup but would use a small tanked heating device, such as the Triangle Tube Elite combination heater for hot water. Rough cost estimate, $3500.

For both the second and third alternatives, we would work with heating contractor to ensure that the unit dhw device could be switched over to a indirect tank scheme with a boiler at that point in the future when we felt we could switch the hot air system to hot water. We have a long term perspective investment perspective and are especially concerned about the most energy efficiency of all alternatives.

Thanks in advance for any thoughts or comments you may, we consider the Wall an amazing resource.

BobAtchinson

Puzzled in VT

Purchase a low volume boiler with a Riello burner, (which can be upgraded later to a higher output), for the smaller unit, and a very efficient indirect water tank, or perhaps a reverse indirect, such as a TurboMax. This would allow you to have the capacity for heating one or both units with the boiler capacity, and these could be brought on as the furnaces either fail or become obsolete.