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Posted by HeatPro on July 15, 2007 at 17:44:58:
In Reply to: Re: circulators vs zone control flow posted by Doug on July 15, 2007 at 16:21:00:
: What I’m trying to address is that at any given time 1 to 3 zones call for heat. Rarely are 4 zones or more calling. If that’s the case and I only need say 20-75K btu output is a 140K output always necessary?
+++ Math follows physics here: If you only need 75,000 btuh output, the thermostat shuts the burner off so that is all you'll get. If the boiler has 140,000 btuh output, then the burner will run only half the hours of the coldest days and MUCH less on warmer days.
In dealing with Stonehenge designers, the bigger the rock the better. However, that isn't necessary in modern heating. You don't need a boiler with twice the input of the output. That GUARANTEES more inefficiency than the 'right-sized' boiler.
There are, however, partners in this farce, as there are not many boilers installed that are made with burners that have .65 nozzles, though installers will feel MUCH safer with nozzles twice that size, even though the majority of new houses with modern insulation need only 25 btuh per square foot which means a 140,000 btuh boiler will heat a modern-insulated 5000 sq ft house just fine.
: The Valiant boiler (oil) is 15 years old and works just fine and is 86% efficient, I am told. Could I benefit greater from new technology boilers, which modulate between outputs A to 145K enough to justify the expense? I also have NG in the house as an option to switch over if that makes better sense.
+++ There is a benefit, however HOW MUCH it is worth has play. If your fuel bill is $2000 a year another 10% in efficiency will get you $200 savings. $200 a year doesn't pay off a $6000 purchase very soon. Maybe grandkids would see the return. It's a 'tough row to hoe' for marketing managers today still selling on old blurbs about 'mine's much more efficient" today, as almost all boilers leave the factory at 84% or better, and condensing boilers are more expensive to get only 10% more.