Our house has a similar situation. It's 1900 sf, built in the 1890's, has some blown in insulation in the walls (we only know this because we gutted the bathroom and found it - this room will have regular batt insulation in the walls and ceilings), has the original windows but triple track storms. The old oil fired boiler is 199k BTU and our oil bills are completely heinous - we used about $650 worth of oil for the month of December. I can't imagine what our bills would have been for a house 50% larger. Just from a reality check standpoint, there is no way a house the size of ours requires the absolutely largest residential boiler available (there may be some slightly larger but in general, around 200k is as big as they get). Our old boiler does short cycle too, it's loud enough that you can hear it. Even in the dead of winter with single digits at night it cycles on and off. We are probably running somewhere in the 60-70% efficiency range also. Everyone who has quoted for us has universally said "WHOA that's a HUGE boiler for your house." After evaluating all of our options, we are going with a modulating/condensing boiler at about half the capacity (maximum) and putting zones into our house. Right now when it is 68 downstairs, it's about 80 degrees in our bedroom - so at a minimum breaking the house down into different zones for upstairs and downstairs should also help - DH works at home during the day and there is no reason to throw all of that extra heat upstairs when no one is there in order to keep downstairs comfortable. For various reasons we are actually going with more zones than that (the way our system was originally piped makes it extremely easy - labor wise it would be just as much to combine them back into one zone as leave them split - and there is a big temperature difference between the various parts of the house we are splitting off) but you might want to check into whether it is possible given your current piping to separate your 2nd floor from your first into separate zones. Between the zoning and the much more efficient boiler, we hope to slash our energy prices. It's NOT a cheap boiler (the cost of the boiler is more than the cost of your boiler + install) but with our old cast iron radiators with relatively cool return, the condensing part will work great, and with us zoning out our house, the modulating part should work great too (it operates at a much lower BTU if the demand isn't there). It also changes the temperature of the water sent out into the system based on the outside temperature, so if it's 50 degrees outside and we want to maintain say 70 inside, it's not necessarily moving 180-190 degree water through the system, so there is savings there too, especially in the shoulder months. We are switching from oil to gas (it would cost us thousands to replace our oil tanks, the real reason we are replacing the boiler - the oil tanks are not long for this world and because there is no longer outside access to the basement it would be a huge job to get the old ones out in pieces and multiple small new ones in and we decided to put that money into a more energy efficient boiler rather than use the same old boiler and just get new oil tanks) so it will be interesting to see the difference in our energy bills. Anyway it took a ton of research and a bunch of time looking at our system and figuring out what was going on to trace out the various loops we have, but I'm glad we put the time into it. We feel confident with the system we have chosen and hope our house will be far more comfortable and energy efficient for the years to come. Energy prices have nowhere to go but up, unfortunately. We are only planning to do this once so figured we'd do it right the first time. The first couple of contractors wanted to put in either a 200k btu boiler to replace the one we have or a 165kbtu boiler calculated by counting radiator fins. As I said before, some of our radiators have about 3x the capacity actually required for comfort in the room so it's kind of silly to oversize in this way because it's just easier to "replace in kind."

Thanks for the feedback. I should mention that the 2,500 square foot figure I gave includes my finished basement. The company that gave me that estimate did survey my house, i.e., took measurements of not only each room but also all the windows. The existing boiler says it has an AGA ratings of 165K (input) and 132K (output). The guy who gave me the estimate did mention that he was recommending a larger (higher BTU) boiler because the original one was only intended to heat the main floor and the upstairs (the basement has been finished since the old boiler was installed). Does 195K still sound very high? We have a combination of the old cast iron radiators (upstairs) and the baseboard-fin-tube type (main floor and basement). Does that recommend against a more expensive high efficiency boiler?

Dear forumites, I live in a condo (one of 3 units in an old house) in the Northeast. We currently have steam heat using oil. We have one tank and one boiler, for the whole house, which is probably 10 years old and in decent shape. The units share the cost of the heat. We're considering changing to gas because of high oil prices, environmental concerns, and U.S. oil-dependency concerns. We can get a new high efficiency gas boiler from our gas company for $799 (or a less efficient for $499). We had an installation contractor come out and he said it would make more sense (cost wise) to stick with one boiler for all 3 units rather than install separate boilers for each unit. He gave a very rough estimate of around $5,000 for the conversion, including the cost of a $799 boiler (I should mention we have a gas line to the house and run our hot water heaters and our stoves on gas.) He also said, given the age of the boiler, that we could put in a conversion burner which would be cheaper but since he doesn't do those he didn't offer any more information. My question is this: should we just add a conversion burner or should we replace the boiler? I understand that using a conversion burner will result in a loss of efficiency but is it safe to do so? It seems to me that the boiler was made to work with oil. We're interested in not just spending less on fuel this winter but also in being environmentally responsible. Is an oil boiler with a gas conversion burner likely to emit more pollution? Thanks for any advice!

Capedude, you have started down the path that would be called a layman's explanation. My knowledge of the DHW and boiler standards is obviously limited. That said, I deal with various types of industrial standards now and then and I have learned to understand how they work. My read is that the boiler standards are fit to combination steam-hot water boilers. The water heater standards are more restricted to appliances that make hot water. Many, if not most, jurisdictions allow the installation of water heaters (Z21.10.3) to power hydronic heat. That means that many officials have decided that they area safe for that use. It boils (he he) down to the question of which set of standards is a better match to an hydronic (hot water) heating system? Is it a set of standards for appliances that make hot water on the one hand, or on the other hand, a set of standards for appliances that can make hot water or steam. If code-compliant, the Westinghouse or HTP Pioneer option makes for an inexpensive way to graft a very efficient boiler into an archaic system without the need to install additional piping (primary-secondary) for boiler protection. You have a buffer built in eliminating the need for a separate buffer tank to prevent short cycling in the case of small zones. The design of the heat exchangers in these water heaters is unique. it looks like they use the inherent stratification of how water in the tank to set up a counter-current exchanger. If you don't like the water heater aspect, a Versa boiler with Z21.13 can be installed if it is not too big and you can stand the additional coin. The physics of the HX are the same as with the water heater. Reports I have seen indicate that even though they may cost more than some other efficient boilers, the amount of money that you can save in repiping (buffer tank) and controls more than compensates for it.