Thanks for your responses. I am sorry that I did not respond sooner. I think that I forgot to check the email notification box. Dad seems to have settled down a little. I think that he had in his mind that he needed to decide and get something done before the deadline for signing up for a seasonal budget and pre-paying for the season's oil. That package has worked out well for him in the past. If he needs more oil this fall before he gets a changeover, he can just pay ala carte. He has not missed a bill in 50+ years so the'll pump him some oil and send him a bill. Dad has always been very objective and detached about making decisions about how much to invest in things with respect to his lifespan. Few people can do that. We'll see about the green bananas. It seems like venting may have to go through the original chimney even if we have low temp flu gas from a condensing boiler. I don't think that there is any reasonable way to get out of the basement sideways without landing too close to a window. Then there is the snow depth too. A separate water heater would invoke the same problems, only double. On the unfinished end of the basement outside there are a porch, and breezeway with concrete blocking any access. On the third side is a deck and a sun room full of windows. I guess that there are lots of options for gas heat beginning from a simple burner change through a reasonably efficient gas boiler to a modulating/condensing boiler. If I am reading the existing boiler plate correctly, we'll have about 60% efficiency by plugging in a new gas burner. I hope that someone will confirm that. The least expensive replacement boilers must be about 80% efficient and would run through the same clay-lined flue? Next up would be a condensing boiler that would run in the 90%s. I have no idea what the relative costs might be. We should be good with the honesty factor. It is strictly small-town and contractors need to maintain reputations or they won't last. I've approached a guy that I went to school with that I am already talking with about a backup genset. The oil company probably won't jerk him around, but they may not have the knowledge or the enthusiasm, hard to say. The genset is another story. Dad should not really be hauling out the 4 kW Coleman and stringing extension cords for sump pumps and the waste water lift pump any longer. NYSEG is good, but with power failure he can't run any water since the septic went away in favor of a village sewer system.

Your "side channel" would be called a "flue" I guess that you have more than one flue in your chimney. Another is other for a fireplace or wood stove? In contrast to your furnace, more modern fossil fuel-burning appliances recover most of the heat from the combustion gasses. This allows the use of plastic pipes to carry the flue gas, sideways, to the outside of the home. The water combustion product is condensed to recover heat (adding to the efficiency) and needs a drain or, sometimes, a pump to a drain to dispose of it. Gas domestic water heaters come in older, lower efficiency and more modern high efficiency varieties as well. You choose low efficiency and a flue pipe to the roof, or high efficiency can go out the side. Your gas dryer can go out the existing dryer vent assuming that you have one and are not venting the dryer to the inside of the house. In some cases the home's heat and hot water can be produced by the same boiler. Hydronic heat (radiators) and domestic hot water are often done in combination this way. I am sure that can be done with forced air heat provided with a heat exchanger. What I don't know is if that makes economic sense compared to a separate water heater. Some pros will chime in what that, I am sure. Don't forget the lower maintenance that mike_home mentioned. With gas you won't need frequent visits like you did from the oil service tech.

Your plumber giving you the load based upon the amount of radiation is actually ok. You will get X amount of btu/ft of radiation. If that has been heating the house then ok. In fact, if the house has been warm then the boiler may as well be sized to the amount of radiation. Anything more is excess capacity. I had a Buderus G224 with their outdoor reset program, which you want, for 12 years and it was excellent. I'd take a Buderus over the others. Undrstand that your chimney is an issue. You say it is not lined. In order to use a "chimney" unit you will have to put an appropriate sized liner installed in your masonry chimney. The staight masonry chimney will not meet the code. You don't want a direct vent or a higher efficiency unit and I understand your reasoning, BUT. Consider the cost of the liner for your current chimney to bring it up to code. Add that to the boiler install cost and I think you will be in the price range of a wall hung condensing modulating boiler. The efficiency of which will be 95-96% vs your proposed 80-82%. BTW the outdoor reset system will vary the output temp of the boiler as the outdoor temp changes. You do not need the same output temp on a 45* day as you need at a 10* day. If your contractor says your current chimney is ok, he is wrong.

Adapting a modulating, high efficiency boiler to an old system can be tricky. For starters, you need a heat loss estimate for the house and you need to determine your room heat exchanger capacity (radiators/convectors/hydrofoils). The latter needs to be done zone by zone if you have a zoned system. Is your baseboard fin-tube convectors, cast iron radiator or something else? Honestly, if you can use a low mass boiler, I'm biased to a system that uses the same boiler for DHW with an indirect tank. It simplifies and cuts down on maintenance costs. You can probably get a rebate on the indirect. Besides, are you gong to take a shower in a freezing cold house? With a small house and a low heating load, it can be hard to get a small enough boiler that produces enough DHW. (You might be thinking that argues for a separate water heater. Maybe, but there are other solutions.) Getting a system with lots of small zones matched to a boiler large enough to heat the whole house can be tricky as well. If zones are not needed for comfort, a good system designer will combine zones sometimes when installing a modulating, HE boiler. Probably the paramount thing to keep in mind that to get anything out of the condensing ability of a hight efficiency boiler, the return water needs to be quite low temperature. That is most easily attained with cast iron radiators and excess radiation capacity so water temp can be held at a minimum. If you have an old house with lots of window and insulation improvements, that is an easier target because radiators were probably not removed. If you have an old, leaky house with few improvements and with fin-tube radiators, it might not be worth installing a high efficiency boiler. They are more finicky, may not last as long, and you will get nothing out of it compared to a mid efficiency boiler.