Experience with high efficiency boilers


Trying to get ahead of the curve here. Heating season is approaching and my boiler is old. I doubt I will replace it until absolutely necessary, but when it happens, I will need to decide what kind to get. House is about 2400 sq ft and climate is fairly severe (Chicago). Hot water heat, natural gas fired. Have separate water heater for domestic uses. The boiler I have now is a Peerless unit from the 1980s.
I see you can get units that are 95% efficient, with sealed combustion chambers and stainless steel heat exchangers. All of those sound like good ideas, but how are they in practice? Do your fuel bills drop? Do they give trouble? Do they last? Are they worth the extra $$? -- H
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Those are the million dollar questions. Condensing boilers are very efficient, and will save on fuel. The big question is how durable they are, who services them, and at what cost. I recently wired a triangle tube gas condensing unit and the customer asked me those questions. I couldn't answer the question. I wire boilers but know very little about the internal parts in these high tech units. Typically, I finish, flip the switch and the unit works, and if it didn't, I wouldn't know where to start. On this particular job, it didn't work, and I spent a lot of time on the phone with a tech from the manufacturer, ironing out error codes that meant nothing to me without whatever bible he was reading from. Ultimately, it turned out to be a shorted cable to an outdoor sensor, but what a waste of time. Had it been a typical mechanical boiler, within 15 minutes, I, or any boiler tech, would have figured it out. Personally, I think these things will become mainstream, and very standardized, but I'm not quite ready to run out and get one. Another thing, some of these companies, like Buderus and Energy Kinetics have specialized training for their equipment, and seem reluctant to answering questions from non trained folks like me, which I think just narrows down the number of people qualified to work on their equipment, and of course raises the cost for hiring those with training.
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Bob Walsh had written this in response to http://www.thestuccocompany.com/maintenance/Re-Experience-with-high-efficiency-boilers-395314-.htm : Condensing boilers are the most efficient boilers on the market. They allow huge energy savings compared to conventional boiler versions, and there are countries beginning to require the use of boilers to be of the condensing type. Conventional boilers convert 60% or less of their fuel into heat. The efficiency of new condensing boilers are above 90%. Talk about huge energy savings. How condensing boilers works Condensing boilers are named such because they "condense" the exhaust gases or the water vapor present in those gases, extracting heat from it and reusing it in the process, instead of letting gases and water vapor get away through the flue.
The secret of these boilers is based on their brilliant designs, which are the larger heat exchangers. Heat exchangers ensure maximum heat extraction, and eventually, minimal losses of gases. There are some restrictions concerning the type of condensing boiler, all depending on your existing heating system at home.
This is where you will require the expert advice and services of a registered boiler engineer. Installation should be done by a qualified boiler engineer who is gas safe registered as they will able to advise you on the best type of the condensing boiler fit for your home.
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On Dec 18, 4:45 am, snipped-for-privacy@gmail.com (Bob Walsh) wrote:

Conventional boilers are about 82% efficent, huge savings no but long term yes. The maximum operating efficency of condensing is near 140f, by the time you reach 180 f % efficency drops about 5%. If radiators were oversized so you could run 140f all the time they would run at their potential.
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http://www.thestuccocompany.com/maintenance/Re-Experience-with-high-efficiency-boilers-395314-.htm
Hi Bob
As you may or may not know that I am not HVAC person,
However I am Environmental test Equipment Tech.
I am interested how this works. It seems to me what you are
Saying that this boiler reusing its own discharge gases by looping
It back into combustion chamber m'I assuming these correctly
Or m'I all wet?

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Me, well, I block all posts from the Sucko Company. I wouldn't believe anything there.
The problem with high efficiency heaters, is that the flue gasses aren't hot enough to carry up the conventional chimney. So, they add an inducer fan. The condensing comes, because they are able to cool the flue gas enough to condense much of the water vapor. That resulting liquid condensate has to be drained some where. Sometimes outdoors, and sometimes into a sanitary sewer.
--
Christopher A. Young
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Need some more info to give you a complete answer.
Clearly you have hot water heat, but what kind? The issue is that condensing boilers maximize their efficiency when their return water temp is below 130 F. If you have a baseboard system, you will never see temps that low, and, even with radiators, you probably won't be able to heat your house in cold weather with water temps like that. The question is "How much efficiency do you lose at say, 150F for a water temp?" If it is a percent or two, no big deal, but any more than that really starts to affect the payback. Given that these boilers aren't typically expected to last more than 15 years (give or take), and they cost about twice as much, it is hard to make the numbers work unless you have radiant floor heat, which operates at lower temps.
You also have to be careful when sizing and setting the temp for domestic hot water, since setting the temp sky high will give you faster recovery, but affects the efficiency also.
JK

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I did a little more research on the topic, and here is a pretty good article on it. Looks like the answer is that a "condensing" boiler operating at high temps is only about 88% efficient, or about 4-6% more efficient than reliable, long lasting, cast iron.
JK
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Hardly going to pay for all the extra doodads that are sure to break down regularly.
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Thanks for the info - what is the URL for the article?
I have cast iron radiators and big old iron pipes serving them - I think the system was originally a gravity circulator. When the weather gets good and cold and the unit runs for a while, the thermometer on the boiler gets up to maybe 180 or 185; I assume that is the temperature inside the unit, not the return temperature. I don't know what the return the temp is. But can't you adjust the set points so that the system runs cooler (but for longer)? (Or, could you adjust the pump size or speed so the water has a longer residence time in the radiators, thus returning cooler?)
Of course there is always uncertainty about gas prices going into the future, which affects any such calculation. -- H
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wrote:

Thanks for the info - what is the URL for the article?
I have cast iron radiators and big old iron pipes serving them - I think the system was originally a gravity circulator. When the weather gets good and cold and the unit runs for a while, the thermometer on the boiler gets up to maybe 180 or 185; I assume that is the temperature inside the unit, not the return temperature. I don't know what the return the temp is. But can't you adjust the set points so that the system runs cooler (but for longer)? (Or, could you adjust the pump size or speed so the water has a longer residence time in the radiators, thus returning cooler?)
Of course there is always uncertainty about gas prices going into the future, which affects any such calculation. -- H
You can cut down the boiler temp on the operating aquastat, which will cause the zone to take more time to satisfy it's thermostat. You can also get outdoor reset devices like those made by Tekmar to adjust boiler temperature for optimum efficiency depending upon outdoor temp and demand
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Yes, they work and yes, the fuel consumption can drop considerably. Every manufacturer has some good units, far more efficient that anything from the 80's. Last year I upgraded to an Energy Kinetics System 2000. For the first few months I save 32% and with the summer hot water use only it will be even more.
Be sure to check on rebates, low or no interest financing and so forth. There is a $1500 tax credit if you do it this year too. With state financing, I'm able to pay for my system strictly from fuel cost savings. YMMV.
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i dunno, but... remember if you upgrade to buy alternative source of heat for your home for a power failure. you may already own a natural gas stove either with pilot lights [or one which allows manual lighting of the oven and top burners without electricity]. you may already own a natural gas water heater with a pilot light which can provide hot water without any electricity. explore upgrades to your heating system carefully: your location with chicago's winter weather suggests it will be very wise to purchase or design a replacement system if it runs from the same voltage (12 VDC)as your car; you could have an emergency cable in your car with its winter gas tank full running safely in the driveway (much quieter than most emergency generators) to operate your new heating system if its operating amperage is low enough to run off the car's cigar lighter fuse or battery jumpers. and buy 5200 btu electric heaters with thermostats for when the new heating system breaks down but the lights are still on. insulate and windproof your home for winter with a reputable contractor. "According to the National Weather Service, Chicago's highest official temperature reading of 107 °F (42 °C) was recorded on June 1, 1934. The lowest temperature of -27 °F (-33 °C) was recorded on January 20, 1985. Along with long, hot dry spells in the summer, Chicago can suffer extreme winter cold spells. In the entire month of January 1977, the temperature did not rise above 31 °F (-1 °C). The average temperature that month was around 10 °F (-12 °C)." see: http://en.wikipedia.org/wiki/Chicago#Climate also, more about heating degree days: http://en.wikipedia.org/wiki/Heating_degree_day and heating degree days for your town for january 2009 at midway airport were 1475 (buffalo ny 14214 was 1433 that month): http://www.degreedays.net / -b
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