Munchkin MC-80 CO, C02 levels

Wally96

Greetings!

In my original Munckin Contender installation manual ( 2007 ) it recommends 8.5% -9.5% C02 levels on low and high fire.

The updated manual on the HTP website ( 2022 ) recommends 8%-10% on low and 8.5%-10.5% on both mid and high

I have the dungs valve and not the new replacement model. Which setting should I follow.

Thank you kindly...

Jamie Hall

Not much of a difference, is there?

EBEBRATT-Ed

Not enough difference to make a difference

Wally96

Thank you for the feed back. In various threads serviceman mention tuning to the high side so I was curious why HTP made the change.
This will be my first attempt at using a combustion analyzer after installing a new heat exchanger.

Unfortunately local companies here do not like working on residential boilers and the commercial guys who know how to tune are too busy so I am learning how.

Thanks again!

Teemok

Back when munchkin's where being installed new I found tuning near the center range of recommended Co2 was not ideal and Co was higher than spec. At first I thought it was just the flue differences of my specific installs. The ignition quality (sound), low fire flame stability (flutter) and the flame and igniter rods suffer with lean mixes. Flue installation and termination problems are the most common problems with all mod-con appliances. How and where it is terminated is critical. Site specific wind eddies can a problem even with correct terminations. Be sure yours is right. The right pipe size. No exhaust re-breathing. Not too long. Not too short. Sloped correctly with no traps. Tune to the rich side. For future reference, the gaps between the coiled water tubes must be open and clean before tuning. (cleaning tools and techniques vary)

Wally96

Great info TEEMOK !

This is a slab single story home and the flue goes straight out of the roof by the book.

I learned my lesson on cleaning the coils. There is occasionally small chunks stuck between the coils and is surely what caused the corrosion and leak. I cut open the old heat exchanger and the inside was shiny so definitely started from the outside.

I will report back on the tuning....

Teemok

There is an industry ignorance around the material found inside these heat exchangers (not limited to HTP's versions). "Coffee grounds" is the term used. As far as I can figure out with my limited skill set they are a by product of stainless steel decomposition related to flame exposure. That leads me to think flame side metal deterioration, temperatures outside of design and cleaning stress is what I think make for the primary life span limitations. There's a PVC is the cause theory, a low grade stainless theory, an acidic condensate theory and more but no scientific proof I've seen. There's no incentive to share it with the public if it has been done. I've cleaned enough of them that my procedure is very fast. Every use scenario/tune/fuel type/ intake air quality has a different HX cleaning need interval. Clean it before you are forced to and be kind to the tubes. I use a thin putty knife bent mid knife at 50 degrees or so and trimmed to be about 7/8" wide as a cleaning tool. Knock sharp corners with a file. Some knifes break some bend well. CLR and round plastic brushes on a 1/4" drill extension. I remove the back fire wall if I can and use ceramic grease on the Allen bolt threads; otherwise, I have a shield plate that fits in to protect it. Flush well with water and sprayer. There's lots of build up materials on the exit side of the coils that clogs the drain at the back. Your type of application is where I've seen the longest lived munchkin.

Wally96

Thank you for the cleaning instructions!!

My first shot at using a new combustion analyzer. I ran it to high and low fire several times and gave it time to stabilize so these readings should be somewhat accurate.

Munchkin MC-80 natural gas, radiant heat application, new heat exchanger.

High Fire
CO 132
CO2 9.49
Flame rectification (d7) 9.4

Low fire
CO 60
CO2 9.94
Flame rectification (d7) 8.8

Low fire CO reading is high?

EBEBRATT-Ed

Both Co readings are high. over 100 CO is NG, 50-100 ok to run but not great, below 50 is where it should be.

Wally96

Where can I find a step by step manual on making the CO, CO2 adjustments. Thank you

Teemok

That looks familiar. Describe the flue and intake, length and fittings. The manual has a diagram showing the throttle vs the offset. Don't mix them up. Your offset could be off a bit. The adjustment is very sensitive. Very slight movements makes a big difference. Important ***** First mark the adjustment and the housing precisely where it's currently set. Write down every adjustment so you can return to the exiting setting if needed. I can't find a factory guide. HTP tech support may help you and is the safest way. If you are brave and want to learn you can read on and try your hand.
Learn how to get in service mode. First get your high fire reading right then drop to low for offset adjustment.
This is a general procedure I use on triangle tubes. Picture a bell curve. Turn the offset screw one way and you move off the peak to one side of the slope. Turn it the other way and you move off peak to the other side. You are likely near peak on the good side of the slope right now. If you are on the good side slope turning the screw clockwise should increase Co2. Adjust and note the reading change. It looks like you need to turn counter clockwise (top to the left) 1/32" at a time. You want the low fire reading to drop and be in the range of just the same to 0.2% leaner/less than the reading at high fire. Any adjustment takes time to be seen on the meter. Be patient. I'd go for 9.25% at high fire. Any adjusting of the offset it will effect the high fire setting so re-tune high fire and then check that low fire is correct again. If your offset was messed with the existing setting could be on the bad side of the curve. Co will be higher and adjustment effects will be reserved. Clockwise adjustments will make it leaner.

Wally96

The flue and intake are completely vertical with no elbows. The unit is on the main floor ( slab home ) and has an approx. total length of 8-9'

Attached is a picture of the termination. The picture is a little deceiving but the distance from intake to exhaust is about 18" so it may not be the 24" they ask for.

Your thoughts? I can easily extend the exhaust..

I hope the attachment works.

tim smith

The earliest munchkins did not like CO below about 80 and CO2 needed to be minimum of 9.2 if memory serves me. I am sure on the CO, If you got your CO below there you would get delayed ignition that some people could hear 2 blocks away. Sounded like a 357 magnum being fired. I usually end up in the middle of recommended these days. 9.5 CO2 or so. Some mfrs still want a minimum of 50 CO up to 130 CO. If I have the latitude of course I want below 20 but not always feasible with some burners. Here is an excerpt from the CPSC re max allowable. Taken right from their verbiage.
I think the current ANSI and AGA limits are 400 ppm air free but of course local jurisdictions can have lower, our gas utility requires under a 100ppm unless equipment mfr printed literature says higher.