Munchkin Diagnosis and Replacement Size Check

SENorthEast1895er

Hi All,

I'm a homeowner with an old Munchkin that I've been nursing along. It recently started dripping off the bottom of the condensate drain tube. As far as I can tell, this is only happening when it's condensing (pressure steady w/ auto-fill valve closed, puddle bigger in the morning).

I opened it up to take a look and didn't want to disturb all the fiberglass without knowing what was going on. So I called my plumber… who also didn't want to disturb the fiberglass and just gave me a quote to replace.

So my first question here is about the drip: Any advice on tracking it down? Or is it, indeed, time to finally replace?

Second question: My current boiler is 140k BTUs and I strongly suspected it was waaay oversized (which I told my plumber). He gave me a quote for a Burnham ModCon that was something like 195k BTUs and said:

• it is only a few hundred dollars of price difference
• it doesn't matter because it has a 10-stage step down and will always be able to fire at the appropriate level
  • which just sounds nuts: why would they make smaller models if that was the case?

Are these statements accurate?

My ChatGPT-assisted estimate of our heating needs (via a few cold months of gas use, degree days, and some math) is about 60k. I want to sanity-check that with a local retired plumber I know and probably redo the math and post it here. But I can't see a reason to get a boiler that's 3.3x larger than I need it to be. And I can see some reasons not to.

Edited to add:

I need to rerun the calculations (which I did; chat gpt just gave me the formula), but it was:

((BTUs used * efficiency) / (degree days x 24) ) x (target indoor temp - design temp)

I'm somewhat familiar with manual Js, having done my best to do it myself when we bought the house. This Munchkin had been running @ 180 for 15 yrs or so (due to a truly terrible install job; my plumber finds something new wrong with it every time he looks closer). I ended up using a Taco ZVC to work around the piping issues to be able to use the outdoor reset (see post history for more info).

And please don't forget my first question: Can I track down this condensate leak? If so, how? (or should I just replace?)

Thanks

Jamie Hall

Lots of reasons not to go with a boiler which is too big. And the idea of replacing a 140K unit with a 195K unit, when you know (I presume) that the 140K unit is plenty big enough — yo do stay warm don't you? — is just nuts.

In fact yu may be able to go smaller — but to determine that you need to know at least vaguely how big a boiler you really do need. There are several ways to do that. There are estimators which aren't goo bad which can give you a good number from your previous fuel usage and where you are located. It is possible to calculate the heat loss of a structure — this is often called a Manual J calculation. In any case you don't need a boiler bigger than what your radiation can handle, usually taken as being around 500 BTUh per foot of baseboard, for fin tube baseboard. For standard radiators, there's another approach.

So find someone who will at least take a pass at actually estimating what size is needed and go from there.

PC7060

Definitely don’t get an boiler. I heat a large house with a 80 K modulating condensing boiler, which often runs at its lowest level.

I wouldn’t be comfortable using ChatGPT based heat loss without verifying the calculations.

What’s the average usage on your gas bills for coldest month for last three years? This give you a ballpark estimate of minimum size but would need to confirm with heat loss report. In my area, temperatures can vary 30 degrees F between night and day / week to week so averaging can be off significantly.

SENorthEast1895er

@PC7060 I edited my original post to include the formula that ChatGPT gave me to use. It all made about enough sense to me. The major questions I had were:

• what efficiency I should use: I used 90%, which is tiny bit under what my boiler was spec'd at from the factory. I think it read that on last fall's servicing report. But maybe I should lower to 88% and rerun
• the "Base Temperature" setting on the degreedays.net report. I left it at default (65)

This year was the coldest winter I can remember; I used the two coldest months (I did match degree days to billing dates), but thanks for the reminder that I should check historical data.

How do you know what level your boiler is running at?