Many times on this site we mention how one of the most important decisions – if not the most important decision – you will make is the size of your new condensing boiler system. A condensing boiler works best when the return water is a perfect temperature allowing you to reuse the condensate it creates. If your system is too large or too small, not only will the return temperature be less ideal, but your system may even have trouble providing you with the temperatures you want in your home. Basically a condensing boiler that is the wrong size may not be a condensing boiler at all!
We mention this because some homeowners may assume that they can easily upgrade a condensing boiler so that it is the perfect size, if they get this wrong in the first place. Unfortunately while you can upgrade some of the controls, the thermostat, the wiring and piping, and other parts, it is very hard if not impossible to upgrade the actual size of the boiler without a major expense. Now we do not want to downplay those possible upgrades – if you do have the correct size condensing boiler system those kinds of upgrades can incrementally lead to positive changes in efficiency and output. They can therefore save you money. But they are only possible and effective with a condensing boiler that is actually condensing.
The good news in all of this is that qualified installers who have been doing this for a while can fairly easily judge the size of the system you need. This is particularly true if the installer has done many systems in your area and with your size home. He or she knows the climate well, and can judge your square footage, air flow, and insulation well enough to lead you in the right direction.