Anyone Have experience with Condensing Boilers?

[430752]

Buying a new house and the boiler is fromo 1983 or so. Still works, and not a complete pig on efficuency (about 83% as far as I can figure), but I'd still like to replace it with something new and more efficient. Boiler is for hot water radiators, not steam. Also the hot water heater is about 9 years old, still working for now.

So, I'm considering a high-efficiency boiler and have seen all the really efficient ones are condensing boilers (where they condense the combustion fumes/vapors to recapture extra heat). They are expensive, but will likely earn it back over time, or at least break even, and there is the added bonus of them being better for enviro (i'm no greenie, but we should all do our part) and also that they're now "smart" with much better computerized control over burn times, lengths, adjustment of flame, etc.

But, i've been reading they're a relatively new product, even worldwide, so they don't have the positive history that, say, a tankless water does in virtue of being used everywhere else in the world first. This is not to say they're prone to break down, just that they're uncertain. Also, many have a cast aluminum chamber, whereas some are stainless stell. There may be one or two cast iron still used in the now common venturi-type design. I've been reading that some suspect the iron or stainless stell will last better than aluminum, but no one ones. But they admit they're guessing and going on preference for pig iron. I'm looking at the Weil-Mclain Ultras, Peerless Pinnacle, Burnham Revolution (?) or if I can afford, a Buderus or Viessman. I'd also like to get an indirect fired hot water heater to further gain efficiency and savings.

So, anyone have any expierence in using or installing these things? Are they all they're cracked up to be? Am I better to just get the latest mostly-efficient cast iron typical/normal boiler and a tankless hot water heater and pocket the savings?

[Garasaki]

The laws of thermodynamics tell us that a natural gas boiler cannot be more then 88% (I think is the number) efficient.

"Condensing boilers" gain efficiency beyond that by recovering heat from the flue gases produced by the combustion process. Under certain conditions, this process produces the condensation that gives these boilers their name.

The condensation produced by this process tends to be very caustic, especially to iron components (ya know how iron and water don't get along so well, throw in some acid and the situation is worse...). Thus the use of stainless steel and aluminum.

It's important to note that condensing boilers are only high efficiency when operating conditions are at a certain point, where the return water is very low temperature, which allows the waste heat to have it's greatest effect. I looked for this information in Burnham's residential literature. I see, no surprise, that it is no where to be found. Look here (a commericial product, same thing though):

http://www.thermalsolutions.com/docs...ure%202008.pdf

ON the last page, you'll see an efficiency chart. As you can see, the 95% efficiency that all the marketing literature will tout is only possible with 50*F entering water conditions. The chances of your system operating at this point are practically, if not literally, 0.

Condesning boilers require that the entire heating system be designed around them, and even then, it's logistically very hard to create a system that allows a condensing boiler to operate at it's highest efficiency.

So, I think for residental use, condensing boilers are pure marketing buzz - you'll never see the effiency they put in the brochure plus there is a durability risk.

But something else you can garner from that chart is that boilers operate more efficiently at modulated conditions (note the 3 difference curves, 100%, 67%, and 33%).

So IMO a feature you should look for, is modulation and note the turndown ratio (a 1:2 turndown ratio means it can operate at 50% of full capacity, and a 1:3 turndown ration means it can operate at 33% capacity).

[430752]

interesting....

hmmmm, guess I can see the logic in your post, but I was reading a wiki article on condensing boilers which stated they're now being mandated (or have been ofr a few years) by many Euro nations, which no doubt have systems as old or older than mine.

The one thing I can think that might favor me is that, to my knowledge, all my radiators are on one giant loop. The house is too old to have separate zones (although I might be able to install valves to make zones), so maybe by the time it makes it to the 17 or 18 radiators in the house, it just might be pretty cool (which makes me wonder when I move in how cold certain rooms in the winter will be?). I was reading also in the wiki article that kinda like a intercooler on a turbocharger (but in reverse) they use the cooled exhuast gases (after the condensation recovery chamber) to cool the return water supply in order to try to gain further efficiency.

Well, I guess it'll come to how much, exactly, the unit and install is compared to a modern day version of the standard boiler.

thanks!