Now that my boiler seems to be back online (thanks for the help yesterday!), I have a question about its eventual replacement:
The system we have is a single zone, one pipe, gas-fired steam system. The boiler is the aforementioned Weil McLain EG-75, now sporting a new pilot burner assembly and ignition control module. The house consists of a main part with four rooms up and four rooms down, and an ell off the back. Because the house (from 1676) was originally heated by fireplaces, all the steam piping that goes from the first floor to the second is exposed in the first floor rooms (I guess they didn't want to open up the walls or drill through the post/beam timbers to install newfangled steam pipes!)
We even have a mini radiator inside the kitchen cabinets to keep the water pipes, also newfangled at some point in this house's history, from freezing. There is only one thermostat, but I did install the Ecobee that allows for remote sensors with occupancy detection in other rooms. This at least can average out the temperature in the occupied zones and control the boiler based on that average. Very helpful for when you make a fire in the fireplace right next to the main thermostat! I should also mention that there is almost no insulation anywhere in the house (except the roof of the main part) and that the windows are all old single pane wavy glass.
The situation is that we are planning to renovate the "ell" portion of the house and add central air to this part. The renovation plans also will require the relocation of many if not all of the existing steam radiators due to changes in the floor plan. So there will have to be major changes to the existing steam system, and the question is what the best bet will be for a new system configuration.
One idea would be for the renovated area, to remove all the steam system and install heat pumps that can provide the central air we are planning as well as heating. But if we remove that much of the load from the boiler (which is already oversized, as far as I am concerned), then we will have a half-baked orphan steam boiler with way too much capacity for the remaining radiators. And I'm also not sure if the hot air from the heat pump system will be sufficient or comfortable for our New England winters.
Another idea would be to convert the steam system to hot water. This would give us additional control zones (which would be nice!) and perhaps we could convert the one pipe radiators into two pipe hot water. Not sure if that is feasible. Then, the central air / heat pump setup could be backed up by hydronic - either by a separate hot water coil in the same unit, or by separate radiators or radiant in-floor. Another nice aspect of the hot water boiler would be the option to do an indirect storage tank for DHW. Right now, we have a very basic gas water heater that often can't keep up with the number of users and the length of their showers.
I don't think it is feasible (or in the budget) to convert the portion of the house we are not planning to renovate to something other than radiators (whether steam or hot water), but maybe that is a third option - get rid of all of the radiators and do forced air? The problem is that I really prefer the comfort of the radiators vs. forced air. Hydro air with variable fan speed is much better than forced hot air furnace in my experience, but....
I should also mention that the house has two separate basements that aren't connected, and that those basements are not really that well suited as mechanical spaces for air handling equipment due to the fact that the house is next to a pond and there is often running water in the basement when the pond level is higher than that of the basement floor! There are also two separate not-connected attics, which could be used for air-side equipment.
Anyway, what I'm hoping to get from the group here is suggestions on some overall system design that allows the central air in the renovated part of the house, provides sufficient capacity/comfort, and deals effectively with the orphaned part of the steam system. Any and all suggestions, no matter how "outside of the box" are much appreciated.
If all else fails, we will go back to the six fireplaces!