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Help on New Boiler Size Please
My wife and I are going to install a new boiler in our home. We have a couple of quotes with very different BTU ratings. To figure out what to do I started searching the net. Mostly what I found out was that this is a complicated topic and I don't know anything and that installation is key. Seems like a lot of experts are here and I hoping for your advice.
The House and Current System
This year we moved into a new house. This house was build around 1904. It is stone and stucco. About 4500 square feet over three floors and a full basement . There are high ceilings all the way up and lots of large windows. The current boiler is 225K and was installed in the 1980s. I think the house used to be on gravity feed but we now have a pump on the return line. The house has old fashioned hot water radiators. Some really big ones. There are 4 inch pipes in the cellar part of the system. Most of the house is on one zone however there is a single large room that has its own manual thermostat. The first cold week of the year we found that the house does not get over 62 degrees F, and most of the time it got no higher than 60 degree with boiler going full blast. The water temp is set at 140 degrees. When we questioned one of the contractors on this he said it could go higher, but that we "shouldn't push this old system". The single room mentioned above does better but we do not use it much, so no help. House is in southern PA so it gets cold but rarely below zero.
We had several contractors in to bid on a new boiler. We have two that seem reasonable, however, the proposed systems seem really different. Both contractors measured radiators and took into consideration the windows etc. This is not a price issue. Neither is cheap and I would rather pay a little more than get the wrong system. One contractor suggests two Weil-McLain ECO110Ns (95% efficient) with four system circulators for a primary/secondary system and two thermostats. So 220 total BTU I guess. The other bid is for one Lockinvar Knight 210 and one Lochinvar Knight 150 (360 BTU total?). TACO zone valve Grundfoss circulators plus outdoor sensors.
Obviously there is a big difference in capacity here. Seems like one of these is pretty far off. Anybody have an opinion? Anybody have a suggestion? What questions should I be asking? Anything else you notice? Any help appreciated.