Posted by Harold Kestenholz - Hydronic Network on October 24, 2001 at 09:52:14:
In Reply to: Is oversizing of a steam boiler ineffcient? posted by Steve on October 23, 2001 at 17:43:36:
A gas steam boiler from the 1970's is very inefficient. A major portion of inefficiency is the always-open draft-hood and chimney. Given an AFUE test in the 1970's, such boilers were 60-65 percent AFUE efficient. Oversizing a boiler by 100 percent would not make the inefficiency significantly worse.
A residential steam system is inefficient in its design. The boiler, boiler water and pipes must heat up to boiling temperature on each call from the thermostat. When the radiators are warm enough to shut the thermostat off, all that heat dissipates. Heating a system up as if it were the coldest weather, every time the thermostat calls for heat, is inefficient. Contrast that with a water boiler system tha needs only heat up to 110F in the fall or spring to satisfy the thermostat. The difference is great.
Changing to a new gas steam boiler would reduce standby losses as the minimum AFUE efficiency would be 78% and you could get better efficient boilers than that. However, it would not increase the efficiency of the steam system pipe losses, which are always significant.
You can achieve savings by changing to a new boiler and insulating the house. Changing the system to a water heat system will cut your costs further.