So far I had three installers came to give quotes on new gas HE boiler. Regarding sizing, one said you didn't need to do heat loss analysis and just size based on the current one, the other said he'll come back and do it when I end up going with him. The third one, initially said that it's based on the current one's input BTU. When I argued with him saying that we have no idea if the current one is correct size, he decided to go around the house and do it. But it wasn't what I expected.
He just went around and looked at the radiators and baseboards. Wrote down the size of them and calculated the gross radiated heat from them. From there he calculated the BTU for the boiler, which happened to be the same as the input BTU of the 30 yr old, current boiler.
The heat loss analysis that I know, and expected him to have done is looking at the size of the walls,ceilings, floors, windows, roofs and etc and how well house is insulated etc. From that approximate their heat loss for the coldest winter temperatures in our area. There are a number of online calculation sheets you can use for this. When I did that it came out to be about 50% of what he recommended The total radiation output of your radiators that this guy did is just what your heating system can output in maximum not what your house needs to keep the desired temperature in your house on the coldest day of the year. Heat loss is heat loss not miximum heat capacity of your radiators, isn't it?
I didn't even bother to argue him about it but am I missing something here? What do you professionals do to size boiler for your job?
The other question that I have is how big of price difference there is, let's say between 140k BTU Alpine vs. 110k BTU Alpine? He hinted that it won't be that much therefore sizing is not important- a few hundred dollars? but I have suspicion that it will be more than that. Can any body answer that?