W/M Ultra efficiency

Puzzled???

Puzzled???

How does the Weil Mclain Ultra maintain the 92+% AFUE efficiency rating. I know as the return water temp decreases, the efficiency increases, but the Ultra's are maintaining these numbers with the same test procedures as any other boiler to get the AFUE rating. If I had a baseboard job, using an Ultra, & had to produce 180 degree water with a system designed TD of 20 degrees, does it still condense? If so, HOW, as it is operating above dewpoint. Help, I can't sleep!

Mike T., Swampeast MO

Don't know if this will help you sleep, but I used to stay awake wondering why my and other older cast iron boilers WEREN'T condensing when they NEVER saw return temperatures above 140°--and typically MUCH lower.

My best guess is that not only is the "condensation occurs with return temps below 140°" a rule-of-thumb, it's even a relative "rule".

It seems to be the "watch out" level for boilers that weren't designed to condense in the first place. Boilers that are designed to condense however seem to do so at significantly higher return temperatures than the "rule".

Unless you're in an extremely cold climate with little temperature variance, it seems almost ridiculous NOT to use some form of temperature reset regardless of the type of heat emitters.

If your b/b heaters were designed with 180° average temp and 20° delta-t in mind (as many are) and your climate is reasonably variable (as most in the U.S. are) you should be able to set a reset curve that keeps return temp below 140° most of the time anyway.

R. Kalia

AFUE

I belive AFUE rules specify water temperatures of 140 out, 120 return. The AFUE is not a measure of what might happen at some other temperatures.

LEAD PIPE

Ultra

I have baseboard heat and live in CT the hottest out put temp this year was 164 degrees with the out door reset. So the return was lower than 140. Right now my out temp is 140. On very very cold days my out put temp may be 180 but it didn't happen this year and it got cold. While it boasts 92% I doubt it is a real number, maybe in a lab somewhere, but it did save me a lot of cash this year and I don't regret putting it in.

Ken_8

I would suggest the actual efficiency was greater

than 92%

The reason being, regardless of load, when a boiler starts after a 20+ minute off cycle, it starts with ambient return water temp and slowly climbs from extremely low water temps up to stat satisfaction. During that period of highest condensation, the AFUE number is not even taken since the "standard" requires a warm-up period. It is common for the frequent cool days of fall and spring to be more in the warm up time frame than the so-called "normal" "standard" test period! Other factors are also at play like pre and post purge times. Thermal mass of the boiler is an issue as well. Remember, a modulating boiler has virtually no "off cycle" and therefore the steady state efficiency and the AFUE numbers can be even further apart.

The AFUE is a "standard" that is definitely needed. It is not however the absolute rating many claim. Nor for that matter should it be dismissed - as most euro boiler fans suggest. It is meant to be a guide. And that is exactly what it is.

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LEAD PIPE

92%

Don't they use a flame temp at 3600 degrees when they calculate these numbers? No way are you getting that in a home. I think they use 0 O2 in the flue gas too. I'm new at this so I may be wrong though.

Ken_8

Flame temp is irrelevant.

Combustion byproduct venting "stack" temps is everything.

The assumption is, whatever burns gives off heat. Whatever goes into the boiler must come out either in the stack - or the objects being heated (rooms, boiler water, piping, etc.) The lower the stack temperature - the more energy liberated "inside."

Stack temp is the defining point of actual efficiency.

Plenty of other factors are at work here, but stack temp is key.



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