Really Confused

Jean-David Beyer

"The truth is that most systems are oversized. And quite often even the smallest available boiler is much larger than it needs to be. Why go to all the trouble of doing a room by room heatloss in a situation where multiplying out a worst case loss of say 35 btus/sq. foot on say 1500 sq ft. tells us we need 28k less than the smallest (80k) oil boiler will provide?"

If you have been in the business a while, perhaps you would already know what Scott has said here. Since as a customer, I had only a book knowledge of these issues, so I did a heat loss two different ways, and also looked at the name plate on the Beckett burner in my old oil boiler (70K/hr, 1/2 gallon of oil per hour if it fired continuously, which it could not since it was so oversized; it cycled quite rapidly due to the settings of the upper limit and the lower limit of that boiler even though I moved them 10 degrees apart).

My house is between 1100 and 1200 square feet total; a little over 700 square feet downstairs and a little over 400 square feet upstairs. And, when I was done, I found out that I needed, say, 40K less than the smallest gas burner in the product line I was interested in. In fact, if I believe the Slant/Fin calculator, I need 50K less than the smallest gas burner in that product line. So I am glad the boiler I selected has 5:1 turndown. But I would get more benefit from that turndown if I could have gotten a 40K BTU/hr boiler.

It seems to me that pacing around the outside of the house would not have left the salesman in doubt and suggesting the 105K unit. Considering the cost of the job (removing old oil tank, installing the gas line in the garage, replacing old undersized heating elements upstairs, replacing old electric hot water heater with indirectly heated one, converting to three zones (one for the DHW), and neatening up everything), the difference in my initial cost for the larger boiler was in the order of $700 which is not all that much compared with the entire job. I could have paid that. But I did not like the idea of paying the continuing operating cost of an oversize boiler.