Munchkin (92%) vs Burnham Revolution (87.6%)...questions

R. Kalia

I do understand that the AFUE number does not predict the actual efficiency in a given application, but I don't understand all the different factors that go into it.

I am going to choose between two boilers that will be installed in much the same way, with outdoor reset plus an on-off thermostat to keep the house from getting too hot. The piping will be the same, the pumps will be the same. The boiler choices are

(a) Munchkin 140M, modulating, condensing, AFUE 92%

(b) Burnham Revolution 96M, nonmodulating, noncondensing, cast-iron (but produces low temp water through built-in injection pump and built-in P/S), AFUE 87.6%

Both vent out the side of the house. The AFUE difference is quite small!

The Munchkin will cycle much less because of the modulation; I suspect that this is the biggest difference that the AFUE does not take into account. How much of an efficiency advantage does this provide in the real world? 25%? (I didn't think so.) 5%? 1%?

Are there other non-apparent differences between a modern condensing boiler, and what is basically a traditional cast-iron boiler in fancy dress, that might affect the real-world efficiency in this application?

Many thanks,

TomStayer

Boiler choices

Enclosed is the MZ. It offers built in exp tank, system pump, & air eliminator. Take a look at www.mzboiler.com for more information. See testimonials also.

Happy boiler selecting.

Unknown

The differences

are that the Revolution boiler modulates the flow of water through the boiler bases on the temperature of water that it is dealing with at any given time. It has a simple and familiar tube style gas train and everyday ignition and control components. Boiler warranty is a limited lifetime warranty and is dead simple to service and diagnose with easily obtainable components. I will add that this NOT a standard cast iron boiler in fancy dress. The sections have diamond shaped pins in lieu of the standard round pins and the entire boiler was engineered to be what it is. These have been out for many years now and have proven themselves time after time to be a very dependable product made entirely in the good old USA! Hope this helps.

Glenn Stanton

Burnham Hydronics

DaveGateway

Actually the AFUE difference is quite large

You can't get to 90+ effcencies unless you condense. Pulling out that extra 5% requires a much better heat exchanger or modulation to keep the BTU's down and not blowing out the flue. High temp applications make this even more difficult but some makers claim they can still condense even in higher temp configurations. Of course the boler cost are higher and you need see if the saving are justified over the next 15-20 years.

Mike T., Swampeast MO

Proportionality

Once you've introduced proportionality anything digital in the system becomes your weak link to system efficiency.

R. Kalia

Yes, but what does that mean in terms of real savings? is it important, is there a payback, or is the Munchkin just a matter of getting the latest whiz-bang?

As pointed out above, the Burnham's internal circulator goes faster if the water is hot, slower if the water is cool. That's "proportional" too. But is it as good as burner modulation in the sense of increasing efficiency?

And my original question is, given that everything else is the same, how big a difference in gas consumption is there between the two boilers? About 5%? Or is it likely to be 10%, 20%, 30%...?

R. Kalia

5% is 5%

That efficiency increase may be difficult to achieve, but that does not make 5% any larger than 5%! And there is a loss in terms of system reliability and/or cost.

Unknown

Percentage

That's all going to depend on what you have the boiler connected to! If it is a load with high temperatures, you will not appreciate the 90%+ efficiency. That would require a larger connected load or media that can operate on the low temperatures. The Revolution does well through the whole temperature spectrum efficiency wise without the extra up front investment to do so. Hope this helps.

Glenn

jerry scharf_2

tell us about the rest of the system

The efficiency of the munchkin is very dependent on the return water temp. What are the heat emitters and the building insulation, and where are you located? Until we know this, there's absolutely no way to answer you.

jerry

R. Kalia

yes, I should have described it

Radiators, but significantly in excess of what is needed to heat the house with 180 on a design day. I don't know how much of the winter will be condensing.

Let's assume, though, that ALL of it will be condensing. The Munchkin rating is based on condensing. So will I get 5% (a indicated by the AFUE) by spending a lot more in the Munchkin, or will I get more than 5%?

S Ebels

Other factors

System sizing: You need to do, or have someone do, a good heatloss of your home 1st. While the Munchie has a modulating burner that will be a little more forgiving of being oversized, the Burnham does not. It does however, make up for some of this with more mass and higher water content. If you go with the Burnham, make sure it's not oversized. One thing that folks often forget is that while the amount of heat going out the flue is only 5-10%, you still have to figure 5-10% of what? 100K, 150K, 200K? Take the Burnham for example. If you waste 10% of 100K you have 10K going outside. If the 150K boiler is oversized it not only short cycles, dropping system efficiency, you are sending 15K out the vent when you only need to lose 10K. I hope that made sense. Advantage: Munckin

You should also consider life cycle costs. In other words the expense of annual maintenance and how long the boiler will last. The Munchkin is a fine piece of equipment, backed up by a good company. I've installed quite a few myself and had good results as a rule. That being said........ I'd lay my last dollar on the fact that when the Munchkin throws in the towel the Burnham will still be cruising along just fine. All other things being equal of course. Some here may disagree and cast all manner of obscene remarks in my general direction but I'll stand by that statement until proven wrong 20 years from now. Glenn spoke the truth when he brought up the standard parts issue. Everything on the Burnham gas train is off the shelf stuff. That means off from about anyones shelf. This is the case with not only the Munchkin but most high efficiency boilers. Just food for thought. What I'm saying is consider not only the up front costs and efficiency difference but also what the boiler is going to cost you down the road in repairs. Advantage: Burnham

There are pros and cons each way and I hope I am not confusing you. I'm merely saying there are more issues to consider than just AFUE.

Above all, your primary concern should be the installer and the installation itself. A good boiler installed poorly is no fun. An average boiler installed well will keep your home comfortable for a long time and probably be pretty darn efficient to boot.

leo g_13

hey Glenn

> That's all going to depend on what you have the

> boiler connected to! If it is a load with high

> temperatures, you will not appreciate the 90%+

> efficiency. That would require a larger connected

> load or media that can operate on the low

> temperatures. The Revolution does well through

> the whole temperature spectrum efficiency wise

> without the extra up front investment to do so.

> Hope this helps.

>

> Glenn





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jerry scharf_2

As you thought

The described system is certainly not one that would do the best for condensing. It will still do well, just not outstanding. With radiant systems and low temperature returns, the condensing boilers really shine.

The remaining advantage to the munchkin when you add the vision package is the outdoor reset combined with boiler output modulation. How ever you do it, with an excess emitter system like yours, getting outdoor reset will be key to your comfort and energy efficiency. There are many ways to skin this cat, each with it's beenfits, drawbacks and costs. I like the integrated boiler control flavors of this (munchkin/vision, vitodens, others,) where the burner settings are being made with the most information possible.

hope that helps,
jerry