I just learned from the U.S.Dept. of Energy web site that half of all furnaces and boilers in the USA are either undersized or oversized in private 1-2 family homes.A mechanical engineer,I know indicated that 90% of them are oversized.Given that most contractors either do not know or perhaps due to profit motives do not care regarding the stupid practices of their craftmanship, I am asking that a method be provided to me to allow me to make the proper choice of heating appliance(In my case the right size hot water boiler).Anther source indicated that I multiply my running footage of baseboard heating through my house;ie, 144 feet by the factor of 550 resulting in a totalBTU need of 79200.) Is that factor correct ? Also I have found on the web site's of all boiler and furnace manufacurers I've visited, that they do not list BTU production capability on the various models of various series of these appliances providing instead phrases like "Max InputMBH","Burner Input Modulation-MBH","DOE Heating Capacity-MBH", NET I-B-R RatingsWater MBH",and Seasonal Efficiency AFUE".That is all gibberish to me and perhaps is also the same to contractors.Please help and advise.Thank you.

I just learned from the U.S.Dept. of Energy web site that half of all furnaces and boilers in the USA are either undersized or oversized in private 1-2 family homes.A mechanical engineer,I know indicated that 90% of them are oversized.Given that most contractors either do not know or perhaps due to profit motives do not care regarding the stupid practices of their craftmanship, I am asking that a method be provided to me to allow me to make the proper choice of heating appliance(In my case the right size hot water boiler).Anther source indicated that I multiply my running footage of baseboard heating thru my house;ie, 144 feet by the factor of 550 resulting in a totalBTU need of 79200.) Is that factor correct ? Also I have found on the web site's of all boiler and furnace manufacurers I've visited, that they do not list BTU production capability on the various models of various series of these appliances providing instead phrases like "Max InputMBH","Burner Input Modulation-MBH","DOE Heating Capacity-MBH", NET I-B-R RatingsWater MBH",and Seasonal Efficiency AFUE".That is all gibberish to me and perhaps is also the same to contractors.Please help and advise.Thank you.
The most accurate way to select your boiler is through a heat lost calculation, then add on 10% , because over time the boiler's efficiency would decrease and your house would also lost its ability to hold in the heat... you are very lucky if you could select a boiler with the exact BTU requirement for you home. Let's say your house require min. 83000 BTU and the manufacture only offer 80k and 90k, you don't have a choice but to select the 90 k... I would agree if they said that it is 100%of them are over or under size

MBH: M is a roman numeral. BH is Btu/hr. MBH is 1000's of BTU/hr.

Max input is the burner. The burner can have more than one stage. Hence max is needed.

AFUE: Definition of AFUE (http://www.furnacecompare.com/faq/definitions/afue.html)
Is nothing but efficiency. A higher number means it going to cost you less to operate.

IBR is essentially the amount of heat transferred to the water.

In order to size any heating system properly you nned to do a manual J calculation.

An example program is here:
HVAC Software, HVAC-Calc for Heat Loss, Heat Load Calculations (http://www.hvaccomputer.com/ggindex.asp)

You will have to pay attention to pipe size, flow rates, radiator efficiency to get an idea of the size required. An example text is here: Modern Hydronic Heating for Residential and Light Commercial Buildings, 2nd Edition, John Siegenthaler - ISBN#766816370 (http://www.constructionbook.com/modern-hydronic-heating-for-residential-light-commercial-buildings-2nd-edition-766816370/plumbing-piping-books/)

The IBR rating of the boiler has to be bigger than the manual J calculation to account for losses in piping and radiation. A higher AFUE means a lower cost.

I hope this helps.

There are a few boilers that are adjustable as far as BTU imput is concerned. They let you taylor the size with in reason for each job. I have a variable unit here that works on a outside sensor. It will vary the output to coincide with the weather.