I am told I must replace within a couple of months the boiler in my 2,400 square feet 34 year old house, with 2.5 bathrooms, replaced windows, good insulation, etc. I have 4 bedrooms and we are 2 people still living here. Most likely we will have to sell within 3-5 years and move into something smaller. Apparently the steel boiler has developed some cracks; I did not see them, but the heating company man showed them to my wife.

The unit to be replaced is a 10 years old New Yorker AP-790 with a heating capacity of 149 MBH. It has been satisfactory: excellent on heating (2 zones) but could use a bit more hot water as I like to soak in the tub... but not vital.... Never had any major problems with two showers going at the same time even with two kids in the house and frequently a house-full of guests.

Got three offers:

1. A Burnham V84 at 159 MBH for $5,500 installed. A new expansion tank is included (capacity not mentioned) but I am not sure if this is the same as an indirect water heater. Lots of sundries included as well which I assume should be standard for any installation.

2. A Weil-McLain WTGO-4 at 145 MBH for $5,200 installed, Extrol tank (whatever that is - probably similar to the expansion tank) and again a slew of sundries.

3. A Buderus GB125 BE/30 at 102 MBH (only 100 MBH in catalog for 178/140 degrees Fahrenheit) for approx $ 11,400 plus two programmable thermostats Honeywell FocusPro 5000 at $350 each. Offer not finalized and an alternative for a GB 125 BE/22 at 75 MBH for approx. $9,600 is also under consideration. Wonder if I will ever amortize the price difference by higher efficiency and lower size on the Buderus... but that's for me to decide. This contractor came with a heat loss calculation showing 43,083 BTU. He used the data available publicly on my house. Even had a picture of the house (!!??).

My question: I understand that at an average rule of thumb a 20-30 BTU/H/sqft loss is reasonable, so all I would need is a 72 MBH unit... or less... as a minimum. Have I been running too big a unit for all these 27 years I spent in this house, throwing money down the drain for too much oil? Or is the Buderus guy trying to sell me be a bill of goods?

Someone recommended looking into a Burnham MPO-IQ84 or IQ115 (could not find on the Internet any pricing info compared to the Burnham V84). It sports an 87% efficiency vs. Buderus's 91-93%. Someone else suggested using an indirect water heater and yet someone else believes that the steel tank is a lot better than a cast iron one and that the cracks that the service man showed to my wife were in the “refractory” rather than the steel… implying an ethical problem with the service man? This latter point tempts me to approach the BBB… but would hate to do so on a simple hunch.

I am a former mechanical engineer (not in HVAC) so I am capable to understand the concepts but since I have been doing something else for the last 25 years, the terminology is somewhat foreign to me. A word from anyone who knows (a lot) better than I do what this is all about, and a suggestion as to how I could get an HONEST opinion, would be very much appreciated.