Condensing vs Noncondensing boilers

Alex Ma

The advantages and disadvantages, any opinion?

Mike T., Swampeast MO

Condensing/Non-condensing

Advantages:

1) Can simplify piping/reduce complexity as there is no need to "protect" the boiler from low return temps.

2) Potential for hefty fuel savings. The lower the supply temp, the higher the savings.

3) No need to re-line old flues--they won't be using them anyway.

Disadvantages:

1) Not suitable to all systems. Those with high temp requirements like copper baseboard and some staple-up/suspended applications won't gain efficiency.

2) Initial cost can be quite high.

3) Condensate pump may be required if no suitable drain is available.

4) Heat exchanger and controls are quite variable in design/material quality. Big-name German companies with their high-volume sales and large R&D budgets likely have the edge on reliability but it certainly comes at a price.

Boilerpro

My two cents:

A lot of advantages and disadvantages depend on the application. If you have a system thats needs above condensing water temps most of the winter (around 140F), I don't think you will get nearly as much benefit from a condensing source. That said, some condensing boilers continue to condense up to 170F water temps (ie. Dunkirk Quantum). So it depends on the boiler. Fuel cost is another "depends". On the U. S. east coast I understand nat. gas costs is about 70cents per therm, here in the midwest U.S. more like 35 cents. Another depends is if you have a multistage heating plant that uses water temperature reset. If sized properly, the first stage boiler could be a condensing heat source and have a much quicker payback because it is in use almost all the time and at low water tempertures. Another is service. Condensing boilers tend to be more complex pieces of equipment, so there is more to break down and the parts are often only available through the boiler manufacturer. However, I do believe that if you are looking at the 87% efficient boilers like the Weil-Mclain GV and the Burnham Revoulation, you'd be better off going with a condensing boiler because cost and complexity are about the same, but you get higher efficiency. My current recommendations for most applications where a single boiler is used is to buy a quaility non-condensing boiler, pereferably chimney vented. This keeps the heart of the heating system very simple and easy to maintain and then, if you want improved efficiency, add a tekmar heating system control. With this combination, if the control ever fails (havn't had one yet in seven years) it can be bypassed to allow continued heating. The improvement in boiler efficiency(probably moving it up in the 85 to 87% range) and improved system efficiency and comfort should result in fuel usage similiar to condensing boilers, but at much lower cost and complexity.

Boilerpro

Mike T., Swampeast MO

35 cents/therm

Where in the Midwest? Last two winters we've been about 85 cents and currently a touch over $1.00!

Feel as though we're paying for CA and Enron.

Boilerpro

I guess that's only round here

Last winter we had the lowest midwinter gas price since the mid1970s (about 27 cents per therm). Right now we're about 40 cents. I guess Northern Illinois Gas is doing alot better job of managing thier supply than your supplier. They are supposed to have the biggest storage fields in the country, so they can even out costs. Two winters ago we hit about 90 Cents per therm in the worst month. I guess I might start selling more condensing boilers in anticipation... I told potential clients about 7 years ago that within 5 to 10 years energy prices would start jumping and I hit it right on the head. I look at it this way, midwinter gas costs stayed the same for nearly 20 years in morthern Ill. about 32 Cents per therm in 1978 and about 32 cents per therm in 1998, we're starting to make up for 20 years of no inflation.

Boilerpro

Bill Clinton

Good non-condensing

While I use a lot of, and have been known to espouse condensing water heaters, I have always believed their biggest energy advantages are low jacket loss and abscence of convection through the heat exchanger during off cycle. Give me those and you can skip the condensing. Condensate piping, condensate neutralizers, stainless steel construction problems: who needs em? You can get pretty close to the same efficiency with a good boiler. By good, I mean: high combustion efficiency; thick insulation; minimal convection on off cycles; high thermal mass; tolerance for low-flow and low return temperatures; and great reliability. For now, that means German boilers: Buderus and Viessman. As for the condensing units put out by the same manufacturers: I'll wait and see.

Bill

hr

Pretty close Bill?

I have stuck my combustion analyzer in a Polaris and MZ, gas fired running120 degrees temperatures. Real close to the efficiency numbers they quote of better. Mid 90% in both cases.

Although I haven't tested many every cast iron boiler including my Weil GV Gold run mid to high 80%. I measured 86% on my Weil. Once again close to the manufactures spec. It was pretty easy to "beef up" the insulation around the cast irn block of the GV, wish the factory would do it!

Anyways mid 80- mid 90s is still 10. That will add up over the life of the equipment. Not to mention the ability to run direct into the heater without expensive mixing devices. I'd much rather pipe condensate drains than 4 way mixing valves Don't give up on your condensing "fix" yet. The latest batch of condensing entries look pretty fine. Even the " died in wool ironheads" are starting to notice

hot rod

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Bill Clinton

Yeh, hr, pretty close.

> I have stuck my combustion analyzer in a Polaris

> and MZ, gas fired running120 degrees

> temperatures. Real close to the efficiency

> numbers they quote of better. Mid 90% in both

> cases.

>

> Although I haven't tested many every

> cast iron boiler including my Weil GV Gold run

> mid to high 80%. I measured 86% on my Weil.

> Once again close to the manufactures spec. It was

> pretty easy to "beef up" the insulation around

> the cast irn block of the GV, wish the factory

> would do it!

>

> Anyways mid 80- mid 90s is still

> 10. That will add up over the life of the

> equipment. Not to mention the ability to run

> direct into the heater without expensive mixing

> devices. I'd much rather pipe condensate drains

> than 4 way mixing valves Don't give up on your

> condensing "fix" yet. The latest batch of

> condensing entries look pretty fine. Even the "

> died in wool ironheads" are starting to notice

>

>

> hot rod

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 144&Step=30"_To Learn More About This Contractor,

> Click Here to Visit Their Ad in "Find A

> Contractor"_/A_

Bill Clinton

Yeh, hr, pretty close.

Guess all things are relative. I convinced myself long ago that the combination of jacket losses and convection through hx doomed boilers attached to a bunch of zones to efficiencies in the low sixties and never mind what the AFUE said. That's what made thermos-bottle like Polaris's so attractive. Something like a Viesmann or a Buderus as presently configured probably give a real world 82 or so percent when those losses are subtracted and a Polaris probably gives its advertised 88%. So the gap has narrowed a lot.
The idea of those condensing water heaters is still attractive, but the scars of Voyager are fresh and Polaris, although much better, still has more problems than I like having to fix.

Guess I'm just gettin' old.

Bill

Boilerpro

Say Hr, Does weil

now allow low temps to return into GV? The older GV with Hoffmann mixing valve was still limited to 120F return, according to the factory techs I spoke with last year. Also, An Esbe 3 way thermix valve and extra pump really aren't that much, why use an expensive four way for boiler protection. I don't see how its needed, unless you need system protection too.

Boilerpro

hr

Not sure how Weil

is currently mixing the GV Gold. Mine is a 1994 vintage and has the Hoffmann 3 way thermostatic mixer under the hood. I believe they now use injection mixing similar to the Burnham Revolution, possibly.

Keep in mind the boiler block does not see this cold return temperature. The mixing device, whatever it may be, protects the boiler. In the case of the Revolution the boiler operates at 200 degrees and is able to accept, or blend, 70 degree return temperatures without a problem.

I haven't sold a 4 way mixer in years. I prefer injection or simple 3 way thermostatics, depending on the application.

hot rod

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