Got it. A condensing boiler is sort of like a condensing furnace. If
the temps the secondary heat exchanger are sufficiently high the
furnace won't condense. That's pretty unlikely to happen with air.
You can make it happen with water though.
If the return is hot enough, and I don't know what the magic number is
but I suspect around 160 or so, the condensate drops to about nothing.
I think that's why Buderus rates the boiler with higher returns around
88% and 98% with the low return temps. 10% is about the same pickup
you get with a gas furnace when you start extracting the latent heat
You are correct on this Steve, this is the exact reason that the Gold series
had a little car radiator style thermostat in them, to get the boiler up
above 140F or condensation would corrode the boiler out. We had to replace
every single boiler we installed because the thermostat failed and the
boiler condensed below 140F. The factory rep, Steve Beraldus from PA came
down on our jobs and took an hour too explain why the boilers were only 80
some % and dropped a great amount when the temps got over 160. So, Bubba is
correct about the manufacturers lying about their efficiencies. What was the
Gold series efficiency rated at, 140 or 160F. I believe they did it at
141F; knowing that they were fudging the numbers and most systems at that
time were change outs operating above the 180. The flue temperature did
increase as the water temperature increased, and as we all know, the PVC
piping didn't work very well for water temps over 180F.
Now, I have a Question
For radiant floor heat, how would you keep the temp down on the floor with a
Weil McLain or others that operate at 140F or more? What could I do to
change this without changing the entire boiler?
You can use a 3 or 4 way mixing valve or a radiant mixing block is the
sexy way to go. Here's a couple of links to one Buderus and another
You can do these on a single loop and still have high temp water for a
water heater or a BB loop.
\'I think that I\'m dizzy, and I rather
like it.\' - Pinky
I would use a three way valve. Or maybe a tempering valve. You may
neep to pipe in some kind of by-pass loop. Draw up what you have, take
a few pics, and Ill meet you at Fishbones for lunch. Its on Monroe St
downtown in Diamond City. Bring your checkbook.
Or... consulte a local professional to have an on site look see. :)
ps I call it Diamond City because when the sun hits the broken glass
in the road it sparkles like diamonds. haha
Go to this link http://tinyurl.com/y8kgov No tub girls. :)
Look to the rated output line. There highest efficiency is with a
supply at 122F and the return at 86F. The lowest efficiency, 88.7% is
with supply at 176F and return at 140.
122F is plenty to drive most radiant systems unless it's a floor with
a thick carpet pad. You could even do panel rads as long as you
design for 122 supply.
Agreed and that's why my point to the OP is appropriate. He was
complaining about having to maintain a MINIMUM temp of 140. I said to
him, "They're specifically designed for low return temps. The Buderus
GB142 will give you up to 98% when it's condensing."
I stand by this. The GB142 will delivering up to 98% when it's
condensing. To condense you need low return temps. Below 140
qualifies as a low return temp. Will it get you the maximum
efficiency possible? No, but then we don't know what return temp the
OP is shooting for. We just know he wants it lower than 140. In
fact, he mentions return temps of around 60F. Well below the 86F
required for 98% efficiency. My guess is he's heating a concrete slab
if he wants a supply of less than 140.
What specifically did I say in this case you find misleading, wrong or
You have a little bit of information but dont know what to do with it.
What you might want to do is ask yourself why a boiler rusted out in
only 15 yrs when it should have lasted 25, 30, or 40 yrs or more.
Oversized boilers and improperly installed boilers will rust like
"It aint rocket science you know?"
Have your contractor install a Tekmar boiler reset control. Keep the
min temp at 140F. As the weather warms the boiler temp is lower and
vise versa. You can also cycle the pumps according to demand saving
even more energy.
No. Didnt you understand the part about condensation? If the boiler
water is below a certain point (generally 140F) the outside sections
condensate. Thats a bad thing.
It promotes rust and corrosion on your brand new boiler which can also
lead to premature and sometimes catastrophic failure.
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