Posted by Harold Kestenholz - Hydronic Network on August 20, 2001 at 22:32:59:
In Reply to: Advise for a new residential, gas fired steam boiler posted by Drew Blanch on August 20, 2001 at 20:06:15:
It is not that a steam boiler is that inefficient; the inefficient part of the system is everything else. Efficiency is determined by the amount of energy that is invested in fuel as heat vs the amount of heat you get out of the system where the people are. Before steam heat gets to you, it has to heat up every pipe in the house to 212F or more. Steam pipes have to be much larger than water heat pipes to do the same job because steam is a gas 1400 times larger than the water that was heated. The losses from the large pipes are very high.
A water system boiler only has to heat the water up to the temperature required at the time (most of the time not over 140F), not 212 every time as in a steam system, so the efficiency of the water system is higher. You can't put an energy star on an inherently inefficient system. Salesmen can get you teary-eyed about historic 1900 turn of the century equipment, but it isn't equivalent to a modern hot water system.
Steam systems accept fresh air in the pipes on every cycle, so rust has to be removed from the system weekly. Corrosion is normal, and poor maintenance by unskilled homeowners is normal, so failures can occur more frequently.
Asking how much more you can save on a gas bill by putting in a new boiler is purely speculative, as it is related to the size of the boiler and system. At least you will know that there will be a savings of about $50 per year from the standing pilot if you put in an electronic pilot (if the ignition module can last over 5 years.) If you are sincerely interested in savings instead of antiquity, you would insulate your home to the max and install a water heat boiler system, this could pay for itself in 10 years instead of keeping an ancient technology because the pipes were already installed 50+ years ago.
This is somewhat similar to asking the efficiency you could get if you put a 2001 Ford Escort 4-banger engine in your model T. You wind up with an old, inconvenient vehicle 50 years out of its time. Steam still has its place in industry, so it lives on. For those still enamored of cast-iron steam radiators in homes, consider the condition of children that fall against them. Yes, the steam radiator feels good when it sends the high radiant heat from the exposed metal at 215F, but you can get that sensation from other more efficient systems today - and never hear a hiss or clank again.