What are the Downside of undersized boiler.

alex_11

I am new HO and trying to replace my existing oil boiler to gas.



I did the SQFT steam radiation calculation and it comes to around 285 SQFT. The boiler at 103K BTU generates 267 SQFT of radiation. The next size up is 138K BTU for 354 SQFT of Steam radiation.



The cost of Gas to operate the bigger unit is 35% more.



Therefore I ask the pros which boiler will they go with 138K or 103K.



I am tempted to go with the 103K BTU size but I dont know what implications it will have on the following:

1. Logevity - under sized boiler will not last as long as over sized-assuming the under sized boiler is working hard and running longer to heat the house.

2. Since the boiler is undersized,will it be a EVERYDAY problem to heat the house to 70 degree everyday,or will it be a problem ONLY on EXTREME COLD DAYS.

3. Will over sized boiler run less and make up for the extra gas consumption - since the load is less - meaning my gas bill  will NOT be 35% more but around 20% more..



All replies VERY MUCH appreciated and thank you in advance. As a pro what would you suggest the HO if you were doing the job?

JStar

RE

Did you already figure in a pick-up factor for system piping? Are the mains insulated? If not, that could add up to another 20%. That makes your required output 342 sq.ft. I'd go with the 138K boiler. A little extra pick-up won't hurt any. Undersizing will cause problems, even on mild days. Certain rooms may never get close to comfortable.

JohnNY

You're looking at the wrong manufacturer for your application.

I would go with a Peerless 63-03:

http://www.peerlessboilers.com/Products/ResidentialBoilers/Series63/tabid/114/Default.aspx#dnn_productratings



or a Weil-McLain EG-40

http://www.weil-mclain.com/en/multimedia-library/pdf/weil-mclain-pdf/products/boilers/gas-boilers/eg/eg_boiler_manual.pdf



or an IN4 and just insulate all my mains as best I could.

http://www.usboiler.net/products/boilers/independence/assets/literature.pdf