Munchkin Finished

Alan (California Radiant) Forbes

I knew I was on borrowed time with the Munchkin I installed in my house 15 years ago, so when the heat exchanger started leaking, it wasn't a surprise. I managed to plug the leak with some epoxy to give us hot water while I install the replacement boiler, a Viessmann B1HE-85.

They changed the configuration on these Vitodens boilers and have separate connections for heating and DHW. The advantage is that the on-board pump serves both, so no pumps are necessary on the primary side unless you have some unusual conditions.

Access to the coding allows you to change the output of the pump from 100% down to 50% to match the external systems. In my case, I want to pump at least 8 gpm for DHW recovery, but even at 100%, the pump max's. out at about 6.5 gpm. The same graph holds true for the 120 size boiler, so the on-board pump doesn't come close to the efficient transfer of heat. Am I reading this wrong?

JUGHNE

So then, my power plant 2003 Munchkin wins the longevity contest....knock on wood.

I also service one from 2006 that was just cleaned for the first time this winter.
Surprisingly clean, original spark and flame sensor were changed then.
This one was not piped P-S and also has a too small of a pump.
It should be dead by now.

Munchkins got a bad rap when first introduced, IMO.

Alan (California Radiant) Forbes

I found that Munchkins last much longer with high temperature applications where they don't condense. The acidic condensate on low temperature systems just eats up the HX.

pedmec

why would you lose efficiency due to lower flow? water to water transfer (i'm assuming your using an indirect water heater) is considered 100%. if your talking about the boiler efficiency changing then that would actually increase as your delta t will be greater which in turn would send the return temperature back to the boiler cooler. that would increase the heat transfer and would increase efficiency.

now if your talking about recovery that's a different story as depending on the style of indirect, coil hx or tank within a tank, then that would change. helical coil has a lot of resistance and varies with size of tank and the tank in a tank really offers none so you could max out your flow.

maybe i'm misunderstanding the question.

GGross

Not so much a flow thing, but worth mentioning. With the sensor the Viessmann tend to run a little cooler than most other boilers when making DHW, which is generally desirable for efficiency. You probably know this if you have been installing them, what you may not realize is that the new E series when hooked to a tank with a 3rd party aquastat will produce 194f boiler water, which is a pretty far cry from the old 167 max they used to have.

That all being said I have so far not had any issue with DHW production with the "out of the box" settings using the B1HE-85 and a 42 gallon indirect with the Viessmann sensor.

Edit: if you haven't used it yet, Viessmann has a pretty nifty DHW sizing application on their website.
https://www.vitoteam.com/dhw_sizer/#

pedmec

hey guys, I notice you guys are able to do this but i haven't figured this out. how do you respond directly to a comment from one of you guys. only just jumped on about a month ago.

Larry Weingarten

Hi @pedmec , click on the person's name and you'll be able to have a private chat. Just hit the "message" button. Or, put an @ sign and their name, so they get notified of your comment in the thread.

Yours, Larry

pedmec

don't need to be private just want to let them know i'm responding to them. not to be sarcastic or anything. just to say "yeah, i have had good luck with that boiler too". newbie here. thank you

heathead

Alan,

I may be off base but I think they are maxed at 6.5 GPM because anything higher would exceed the max flow rate through the heat exchanger in the boiler.

pedmec

just like you did to me.

mattmia2

Larry Weingarten said:

Hi @pedmec , click on the person's name and you'll be able to have a private chat. Just hit the "message" button. Or, put an @ sign and their name, so they get notified of your comment in the thread.

Yours, Larry

you can also press the "quote" button under their comment to quote their comment

mattmia2

I have some not fully formed thoughts about this. The manufacturer's specs for flow for the indirect are usually to prevent sustained condensation in a cast iron boiler. You can play with that to get lower return water temps with a mod con. With a big load that will still take all of the heat the boiler can supply(within reason with smaller boilers) with a lower flow but that also makes the final recovery to temp after a big draw or on a small draw take longer. The lower return temps improve efficiency at the expense of a lower total hot water output but it might only be important if you have multiple back to back showers or similar large draws.

pedmec

thanks guys, much appreciated

Alan (California Radiant) Forbes

Stated heat up times are very quick for the different storage capacities and will probably be different in the real world as delivery water temperature from the boiler will not always be at setpoint.

The stated maximum flow rate for the boiler is 5.3 gpm at a 30°Δ, so that explains the pump limitation.

I also think that lower flow rates are somehow more efficient (less electricity for the pump, perhaps less wear and tear on the boiler) at the expense of recovery rate. Especially with a Viessmann indirect which has one of the lowest pressure drops and highest HX surface areas (except TT Smart series) in the industry.

Alan (California Radiant) Forbes

BTW, the oldest Munchkin that I still service is an 80M, serial #G10H0415, manufactured July 2001. I cleaned it out a couple of months ago and it had hardly any coffee grounds. It heats baseboard.

pedmec

i put one in my own house in 2005. Only until last year did we have any real issue. Had to change the swirl plate a couple of times but that was it until the 925 control failed last year. funny thing is i haven't cleaned it since 2010 because i got a divorce and the ex-wife has the house lol. i work on the house because she has the kids call me when they have issues and she knows i wont let the kids suffer. hahaha on me

I will say that munchkin did have a rough beginning but i also will maintain that most of the problems were installation related. Not that they were perfect but when you are first out of the gate its trial and error and i think the boilers reputation suffered for it. no techs would accepting responsibility for a defective install. bruise their ego

mattmia2

I hung around here around maybe 2005 or so and remember people disparaging the munchkin, probably mostly because they didn't read or understand the manual. I'm sure HTPs manuals have got much better since then as well.

JUGHNE

Early Munchkin I&O manuals showed piping without P/S would be acceptable/optional.

pedmec

@mattmia2 no kidding, i didn't know that. i waited and wanted to see how everything would work out. early installs of mod/cons and nobody knew anything about start up and combustion testing. so i would do it for other contractors and that's when i saw the issues with installs. they sold a lot in my area at the very beginning. the only thing i didn't like was the keypad. couldn't never remember which combination of buttons to hit to get into programming.