Munchkin boiler and gravity system

smoore

I've heard that it's not a good idea to install a munchkin on an old gravity system due to the small pasages of the heat exchanger which could become plugged by scale from the system.Is this true or could the system be flushed before removeing existing boiler? If so what would you use to flush system and how would you go about it?

kevin

I know...

that a couple of guys here have installed them in old gravity systems. flushing/pre-washing/soaking with TSP would help and add a Y strainer on the return would help too.kpc

kf_2

As a rule...

never install any low mass boiler into an existing heating system without a Y-Strainer on the return side.


kf

Larry_7

We did one

The water in the old gravity system wasn't very funky. There was a minimal amount of sludge and gunk in the very bottom of the sections. We did install a y-strainer on the inlet for good measure. This Munchie has been on line since September without a hitch...yet. The strainer basket will be the first place I'll look if a low pressure fault arises and if not, will surely get pulled in the spring or summer on its first annual inspection. Have seen posts here recommending to run the boiler a week or so and pull the basket.

We've been attempting to moniter the boiler consumption based on degree day records (24-hr avg.)and for the December billing period the Munchie appeared to be eating about half the fuel per DD that the old gravity/conversion burner did. House is around 3,000 sq. ft, 9-1/2 ft ceilings, 2-story and very little insulation. Although these numbers are only as accurate as this DD method allows, they still indicate a dramatic decrease in consumption. Made a believer out of me.

To make a long story short, go for it.

Larry

Brian (Tankless)

New Boiler Munchkin or Slant/Fin Concept 21

I am replacing a oil gas fired hot water boiler. Two recomendations were a Munchkin M80 and a Slant/Fin Concept 21 CB-90.

Any recomendations on which is the better unit? Also what about reliability and service.

Thanks

Boilerpro_3

How about copper tube boilers...

These boilers are often near twins to their domestic water heating siblings that require high velocity water through the tubes to not only achieve proper heat transfer, but scrub the tubes clean of any accumulating lime. If the velocity is high enough to scrub out lime, wouldn't that keep boiler free of all that old sludge?

BTW,I have few Lochinvars, a high velocity, high pressure drop copper tube boiler in converted gravity systems and they are working fine.

Boilerpro

hot_rod

Make sure you monitor those Y strainers

for the first weeks or months. Nothing like a partially plugged strainer to make you think you piped or undersized a job

Install a good full port ball valve on the clean out port, with a hose connection, to flush them into a bucket. See what treasures you find!

hot rod

Ben_3

Copper boilers

Installed many a copper fin boiler into a gravity system. Works great if you primary/secondary the system. Weil-Mclain used to ask that an oversized pipe with cleanouts be installed on the return for the sludge to collect in so it wouldn't end up in their cast iron boiler. Whatever the type of boiler this should be addressed if it's a problem. A nice wye strainer will do the trick as well, like a suction line drier for A/C.

Mark Hunt

Munchkins and gravity systems


I have several of these out there and have had no problems.

Mark H

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Paul Pollets

Matching the boiler

Cast iron boilers work best on gravity systems. The thermal mass of the cast iron radiators coupled with the correctly sized boiler should provide longer burn cycles. Condensing boilers have extremely limited uses on gravity cast-iron systems, in my opinion. It's possible to design the load to condense, but is it the best for the system? Or the longevity of the boiler? I always use a motorized 4- way valve when retrofitting the gravity "near boiler" piping to control the thermal shock

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paul lessard_2

paul could you elaborate?

would outdoor reset be one of those limited uses
you know what I think I get more confused every day.
how could it be bad for system or boiler?
thanks paul. paul...

Boilerpro_3

Paul could you elaborate....

Are you talking about straight gravity or gravity conveted to pumped flow. I've found with the correctly sized boiler in a converted gravity system, you get very long burn cyles (usually about 1 to 2 per hour in typical winter weather) and only about a 20F rise in system temp during the cycle, even when the radiation closely matches the load (assuming 180F water at design). With most converted gravity systems I've worked with the design operating water temp is more in the range of 150F.

Since the water temp changes so slowly due to the high mass of the system and tends to reset itself based on load (shorter burn cycles in warm weather equal very low operating temps throughout the burn cycle), I would think that a converted gravity system is nearly a match made in heaven for condensors. I don't see where the problems lie for pumped conversions, other than accounting for sludge.

Boilerpro

Paul Pollets

Outdoor reset

is mandatory for any boiler system, because of the energy it saves and it's use for reducing cyclying. Since codes rarely specify Outdoor Reset as mandatory, it's optional in N. America, and somewhat of a mystery to many contractors and homeowners. A cast iron boiler typically will hold it's heat 3x longer than a CFT boiler and will give that heat back to the system in "constant circulation" without having the boiler turn on again. A boiler will work at "peak performance", given the right control strategy.

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Paul Pollets

Cleaning Chemicals

Do you use any cleaning chemicals and system flush when commisioning the new boiler? We've found that just about all sludge and mud can be removed with Chem Aqua CB93 system cleaner. 2pts diluted in 1gal of hot water and injected with a Siver King force pump into a boiler drain, will give superior results if allowed to circulate for 4-7 days. We come back and thouroughly drain down and flush, then refill. When the air is removed(after 48hrs) we inject 2pt of CB777 corrosion inhibitor and pump lubricant. Water stabilizes at 6.8Ph -7, and stays there. The product contains a non-toxic red dye, so you'll know if there's ever a leak in the hydronic system. Since the cleaning takes time, a pair of walkie-talkies to avoid having to run a marathon, and a little patience, make sure to include it in the bid!!

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Mike T., Swampeast MO

A modulating, condensing boiler seems to me to have more in common with an old iron solid fuel boiler than a "standard" iron boiler.

Never forget that the old solid fuel boilers WERE modulating and that the systems were designed with this in mind. Hot water had the upper hand over steam in this regard until vapor systems were introduced. Both however, loose this inherent modulation ability when digital boilers are used.

I would venture to say that a boiler sized to modern standards on an old iron system will find the boiler incapable of producing a full system temperature near 180° unless the inside temp is literally sauna-like.

While a cast iron boiler will certainly be able to hold its heat better than other types of boilers, it is only able to retain heat if somehow isolated from the radiation. Old boilers did this with their enormous size/water volume and reliance on gravity flow.

With a modern small cast iron boiler and a circulating pump this ability to retain heat in the boiler is completely overwhelmed by the radiation, piping and volume of the system. What you are seeing is the effectiveness of bypass (or other strategies) at keeping heat OUT of the system. While this might increase boiler efficiency a bit, it increases standby loss in a classic catch-22.

There are WAY too many reports of extreme fuel use reduction when condensing boilers are attached to cast iron systems to be discounted. These savings are MUCH higher than boiler efficiency ratings would imply so there MUST be something else going on...

I say it is because condensing sources are actually more similar to the old massive solid fuel boilers than non-condensing sources. Remember that condensing boilers actually GAIN efficiency with lowered return temperature and iron systems often produce EXTREMELY low return temperatures--so low that other boilers must be protected from ensuing damage.

Reset really is a form of modulation. Remember that early Munchkins could either be reset or modulate their burner--particularly in a system of high mass like standing iron. With a digitally controlled system it really doesn't matter which modulates (the water temp or the burner).

Proportional systems (TRVs, etc.) require a completely different boiler control scheme to achieve their utmost efficiency. Remember that flow in such a system IS a variable--it is not static like a digital system.

I don't want to sound like a Viessmanan Vitodens commercial but it is an absolutely AMAZING machine DESIGNED to make proportional systems as efficient as possible.

It works with the dynamics of proportional systems by varying EVERY component--flow rate, burn rate, supply temp and return temp--all the while sensing outdoor temperature and adjusting these variables to suit what is going on outside. This is EXACTLY what gravity conversion systems want because it mimics the way they operated ORIGINALLY--it has just been completely automated.

Paul Pollets

Topic for Wetstock III

Mike are you attending Wetstock III? This would be a great topic to take up at a Roundtable.
Paul

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Mike T., Swampeast MO

Yep, barring another intervention of fate I'll be there.

My experience is extremely limited as I've only worked on one system constructed after WWII and it used a water heater as the boiler. What I do seem to have a "knack" for though is understanding the dynamics of heating systems. Proportionality and radiation are my fascinations and I believe they are fundamentally linked.

Paul Pollets

Make sure

you get a chance to talk with Chris Rorke while you're there. He'd be happy to share his knowledge about this topic.

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