MZ boiler

masterplumb

Has anyone any experience with the MZ boilers, good or bad. Thinking about going with a condensing boiler because I need the space. If not the MZ then what would you recommend? T.I.A. Chris

Unknown

Good.

The MZ is a fine condensing boiler. I recommend it highly though It's not the only space saving heat source out there and it doesn't modulate. There is something to be said for the tried & true. A simple strong machine that is extremely reliable.

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Ken_8

On a scale from 1 to 10,

I'd give it an 11.

Extremely high quality and near bulletproof design.

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Dave Yates (PAH)

set it and forget it

They're trouble-free as long as you take the time to set them up properly.

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Brad White_2

I have one

which I like (it heats my house and shower water so I had better like it..) I agree on the installation, durabilty and simplicity. But I do have a couple of areas of improvement that I have suggested to Monitor Products.

These issues may be something I am doing/have done wrong, so chime in anybody...in my first full year of use, I saw no difference in gas consumption from prior years between the MZ and my 1985 Burnham Series 2 4-section with Centra 4-way mixing valve. I have limited radiant off a manifold, Runtal panels and some cast iron by the way. House heat loss is about 65,000 not including domestic hot water load.


Here is my issues list:

1) Short cycling in mild weather/low load (30 seconds to one minute on-time cannot be good) even with a buffer tank. I have suggested that they develop a reset control, and have been told that Matt Connolly formerly of Monitor had developed one based on Tekmar. This was told to me about six months ago. I have not seen any more on it since then.

2) On-Off Operation, no modulation or even staging. At 94,500 btu input that is quite a load to snap on and off. One-size fits all until you get to the 2-stage 140 MBH model.

3) Internal circulator (Grundfos 15-42F 3-speed) delivers a boiler-side flow on speed 3 of about 4.5 to 5 gpm. Not a lot of residual flow for the system, so I went primary-secondary. (DHW in parallel via 3-way valve). I replaced the internal circulator with a 15-58 3-speed on speed 3 also. This now flows 6 GPM. Why did I do this?

The minimum flow rate of 3.52 gpm gives a temperature rise of about 52 degrees F. This means in order to stay below condensing for best efficiency, you have to have about 80 to 85 degree return water. (I do not have full radiant floors only a couple of rooms).

At 5 gpm this drops to about 34 degrees F., still requiring about 100 degree F. return water. At 6 gpm this drops to about 29 degrees. F. which is what I have now. This allows me to set the (for now set-and-forget) aquastat for about 135 degrees F. and return above 100 when fully warmed. So I stay mostly below the condensing line.

So....suggestion summary/Wish List is: Modulating Burner, Reset Control and increase the internal pump flow rate. Still a good product.

TomStayer

MZ

Thanks for the post ‘gents’.

Hundreds of homeowners have enjoyed the fuel savings (up to 50%) that the MZ can give. The MZ could be considered a well hung wall hung boiler.

MPI does have an Outdoor Reset Control now available to their customers. The part number is 9110 and is relatively inexpensive.

There is a color sales slick available for those of you who are interested. Contact me at 800-524-1102 or email and I will have it sent out to you.

Bill_29

which is the favorite?

Which would be the prefered brand? MZ of Munchkin?

Phil_6

I LOVE MY MZ ;-)

Have one for going on 4 years in my house, I've installed a couple for customers, and only a couple of little tiny troubles.

Mike T., Swampeast MO

Those are EXACTLY the issues

I had when considering one. Particularly since it would be connected into a continually circulating system with TRVs.

You said, "The minimum flow rate of 3.52 gpm gives a temperature rise of about 52 degrees F. This means in order to stay below condensing for best efficiency, you have to have about 80 to 85 degree return water."

I thought that condensation was much more a function of return temperature than supply temperature, so as long as you keep your return temp down you [should] be condensing nicely regardless of the high temp rise across the boiler.

You have a buffer tank in this system?

Perhaps you can increase the differential temperature between boiler cut-in and cut-out to reduce short cycling.

One other thing that sounds strange and may well have something to do with your [presumed] low efficiency:

Surely the flow rate of the built-in circulator is UTTERLY intentional, giving the boiler the temp rise it "wants" for best efficiency. By increasing the flow through the boiler, you're reducing delta-t and (I'd wager) efficiency as well.

Unknown

This is how we do it;

MZ is an AWESOME heat source.

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Robert O'Connor_5

Gary..

Nice looking job. What's under the towel? I use to sport a similar one over my clutch & fuel pump on the race car. Hiding any wet secrets under there??.Robert O'Connor/NJ

Brad White_2

Hey Mike

Good to hear from you again.
Yes, the return water governs condensing but it BEGINS the process. Highest efficiency is when the entire operating range is below the condensing curve. (Witness snow melting systems running with practially ice water, close to 98% in some cases.) Remember, the leaving flue gasses see the entering return water. Why not start the condensing farther up the combustion train? Try it and you will see a big difference. Start up always condenses more than at temperature.

If I stayed with the standard or lower flow rate, my average temperature was too low to heat the house in colder weather. When I have more radiant floor and radiation, that will change. Part of the process is increasing radiation surface to take best advantage of the MZ's capabilities.


I do not know how to change the cut-in/cut out spread. Perhaps the new mod control will do that. Otherwise, any ideas?

Yes, I do have a buffer tank. 40 gallon versus the 20 Monitor recommends. It is on-line/off line based on return water coming back too high. If RWT is above say, 120F, a pump off of "closeleyspacedtees" charges the tank and prolongs operation in condensing mode.

Increasing the flow rate has increased the efficiency (late last season). Consider at low flow rate (high temperature rise): My return water if it comes back at 100 or 110, it rises to 150 to 160, practically suitable for a cast iron boiler and defeating the purpose of going to a condensing boiler. If I increase the flow, this drops by another 20 degrees, so I stay below 140F in the coldest weather. In milder weather, I crank it down a tad. Looking forward to checking out the new reset control.

Keep in mind too that the first season I used it was with the factory pump. That was when I had no difference in fuel usage from 18 prior years of records. Compensated for degree-days and talking consumption not cost, there was no savings. This year I hope to have it different. Buffer tank in season two shortened the cycling a bit. This year will be the first full season with the larger internal pump. Personally, I would favor a variable pump with external control. Another on the wish list. Simple and effective! Hope this finds you well.
-Brad

Unknown

Wet secerets;

Robert,

Yes I did have a leaker. No auto fill valve so you know I must have fixed it. No magic tricks. Good eye:-)

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