Installing air handler to propane boiler

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drewmo

Feeling the Heat
Nov 20, 2006
360
Topsham, ME
A couple years ago, we removed a defunct oil/wood combo furnace, and have since been heating the portion of the house that this system was tied into with a wood insert. This has worked very well for us and we haven't missed having a "central" heating system. But, for a variety of reasons, we're looking to utilize the existing duct work to get a central heating system back in place.

At the time we removed the old furnace, there was also a rather old oil boiler that served an addition that was put on the house back in the 80s (baseboard hot water). We replaced that boiler with wall-hung Pensotti propane boiler and had it sized so that it could heat the entire house, as well as hot water once our electric tank dies.

We are considering adding an air handler to the Pensotti and tying that into the existing ductwork. This air handler will be capable of 40,000 BTU/hr and 1,500 CFM at a water temp of 170. I believe the calculated demand for this space is 32,000 BTU. There are 4 rooms upstairs (2 @ 12'x10' and 2 @ 12'x12', plus a small bathroom, closets and hallway). Downstairs, we have a living room, studio, and kitchen/dining area.

In theory, this should work. In reality, will it? I never had a chance to use the old oil/wood combo furnace, so I don't know how well that heated the space. My one concern is that the air handler is only reaching a temp of ~170, where I'm assuming the heat exchange on the old furnace was probably considerably hotter (350 or greater). Is this a valid concern?

We have another option of installing baseboard to the remainder of the house, but not only is it considerably more expensive, it would be a shame to not use the existing ducts.

Has anyone faced a similar situation? Any thoughts would be greatly appreciated!
 
We heated our house with a oil fired hot water tank for many years once we got rid of the outside wood stove. I think the trick is to ensure you have a good balance on the system with fan size and an appropriately sized and located cold air return.
 
The HVAC guy says the return is plenty large. Appears they oversized things back in the day. His one comment was in today's design, the registers are on the outside walls with the return in the middle of the house. Our's is opposite, with registers in the middle and return on the outside.
 
Our registers are on the outer walls with cold air return at the bottom of open spiral stairs...
 
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