condensing vs atmospheric

Timco

Availability of parts is what I always hear. For your own place, go high eff, but for a rental, I used atmospheric. Cheaper, and fewer parts with better availability. Bullet-proof. Usually a limited lifetime warranty on CI boilers.

Tim

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D107

any reason NOT to go to condensing?

Have 25 yr old weil-mclain non MOD 7 section gas-fired hot water boiler. GrossInput/Gross Net = 210/165K Btu/hr. Net output 143K. 1924 house, existing 3-column rads on two floors with baseboard in basement = 500EDR; rough heat loss shows about 55K required. Different pros have recommended munchkin, Buderus, some atmospheric-MOD.

Reading the Wall I've seen mentioned some problems with Buderus, Munchkin, but can't say it's more than any other boiler line that occasionally has to be fine-tuned. One Wall posting said the scuttlebut was that the systems with condensing will need careful water treatment to lessen corrosion, etc. I'm also a little concerned with the venting through sidewalls vs. the chimney. Given that the condensing aspect gives me about 15%? or so additional efficiency above the best atmospheric Modulating, is there any reason NOT to go Buderus aside from price? Have they been around long enough to prove their mettle? Last as long as atmospheric? Have so much gadgetry that more things can go wrong?

Thanks,

David

Steamhead (in transit)

Another thing with mod/cons

is they vent thru the side wall of the house rather than the chimney. This may not be possible in some houses because of Code restrictions on how far above ground, how far from windows etc. the vent must be. I find this in older houses with lots of windows.

Oh, and some companies think it's OK to shut down for inventory in the middle of winter when people are most likely to need parts. This results in 3-4 week delays on parts orders. I will NEVER install boilers from companies like this.

Mitch_6

I f you do not have radiant heat

and do not intend to run cast iron radiation at low temperatures there is not as great a difference in efficiency between conventional cast iron and condensing boilers as you would think.

Ya the high teck stuff has a lot of bells and whistles but they have to be piped in just right and like with your car have a lot of sensors that can cause lock outs.

Power venting is another issue, especially hear in the peoples republic of Massachusetts. Myself if I have a good chimny with a good liner and proper combustion air will go cast iron conventional draft every time.

Mitch S.

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D107

Thanks Mitch. I assumed I WOULD be using varied water temps

maybe between 160-180 which as I understand it is what you get from the modulating aspect. I know many wallies discuss much lower temps e.g. 130 etc. I have been told that my situation--old cast iron rads in old gravity converted system was ideal for MOD/CON and outdoor/indoor reset systems--but I have to say the comments on this thread make alot of sense.

With my 25 yr-old old Weil-Mclain in 6 yrs I've had only to replace two circ pumps, and two burner ignition pieces, which isn't bad given it was piped on return side,has undersized expansion tank and near boiler piping, no bypass, no low water cutoff.

Thanks Tim, Steamhead, Mitch as usual for your enlightening comments. I know there's a big buderus/viessmann contingent out there amongst the wallies, but I'm glad to hear the other side.

David

Mitch_6

Temps

160 to 180 is actually the range of conventional cast iron.

set your aqua stat for 180F and it will cycle 180 to 160 as long as there is a call for heat.

Mitch S.

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D107

Thanks; hook it up with indoor or outdoor reset? currently have

three zones; two on honeywell digital 'magicstat'--works well. will have to go to four zones to separate out a cold slab porch. probably do an indirect HWH same time.

i guess what i hear on the wall for atmospheric MOD is peerless, weil-mclain, burnham; i guess buderus makes those too. Some wallies don't like weil mclains for ?rubber nipples is it? and to stay away from the companies that close in Jan for inventory.

thanks,

David

Mike E_2

Mod/Cons don't have to be vented through the sidewall. They can be run vertically through the roof, or they can be run through the old chimney flue as long as nothing else is being vented into the flue anymore.

D107

I've heard that mod-cons require stainless steel liner

if vented via chimney, not just directly through terra cotta lined chimney like atmospheric. certainly added cost.

Constantin

I have a slightly different perspective...

I think you will enjoy a much higher saving on a modulating condensing boiler vs. an atmospheric than just the AFUE difference alone, if the emitters can operate at low temperatures. That's because a modulating boiler will achieve steady state efficiency much of the year.

The need for water treatment is a function of the local water quality. If you have very good water, then it's a non-issue. Otherwise, the Aluminum blocks used in the GB142 wouldn't have survived for all those years that they were only available in the EU. Ditto for the stainless HX's used in the Munchkin, Trinity, Vitodens, etc.

Of course, there is a price to pay for better perfomance in the form of increased complexity, higher potential failure rates, etc. It is up to you to decide whether these trade-offs for higher efficiency are worth it.

D107

thanks Constantin; guess I should check my town's

code re: direct venting to see what's allowed. Hate to have to pay for a new chimney liner if I had to vent that way. Parts seems to be an issue as well, but obviously there's pros and cons to any choice.