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Thread: Is a super high efficiency boiler worth the inital cost?

  1. #1
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default Is a super high efficiency boiler worth the inital cost?

    I've asked this in a different manner before, but thought I'd see what ideas come out now that some time has passed.

    Most boiler lines have at least a couple of "classes" of boilers. Tried and true, simple, fair effficiency and relatively new, super efficient units. The super efficent models get efficencies in the mid-90% range, the older stuff is usually in the low 80% range.

    Is the more complex, electronically controlled high efficiency model "worth" it? With today's energy costs, the difference in initial cost may or may not pay over the life of the unit, but it probably won't if costs to maintain it end up being higher.

    From a comfort viewpoint, the modulating version I'm thinking about, a Viessman unit, gets up to 97% in its most likely used mode, barely running.

    Pros, cons?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Like an engineer alternety's Avatar
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    There are a few details anyone would need to even think about answering this question.

    "With today's energy costs" - If you know the future (e.g., next fall) energy cost you would be making so much money on the futures market that the question would be moot. Calculations for ROI need costs to evaluate.

    The 97% modulating boilers are condensing. They use the return loop of the circulating water to cool exhaust gases to the point where the water vapor condenses to recover the latent heat of vaporization. If the required temperature of the heating system return water is above the condensing temperature, it will not get to the 97% range. You did not specify what your heating system is. Radiators, baseboard, in-floor radiant, etc. (I assume you are not talking steam). Each of these approaches has different water temperature requirements. You need to know your heat loss for the structure, what the required temperature/flow is for your specific installed heat exchangers to maintain room temperature. Your boiler must be sized correctly for efficiency.

    One thing you want to do, if everything else looks like it will work, is to use outdoor reset. This is a sensor that measures outside temperature and adjusts the temperature of the water provided by the boiler. I think the Veissman's come with this but I am not certain. They can certainly use it. The ratio (curve) is in a table in the microprocessor running the boiler. These curves can be adjusted to optimize a particular system. Some vendors and heating contractors will not provide the information needed for the owner to access these functions. If you want to fiddle with it chack before you buy something.

    As with many things, the answer is not simple and requires other answers first.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Primary heat is in-floor radiant with a supply temp in the 120 degree range. Need a boiler big enough for DHW, but heat load only needs 28K btu on a -10 degree day (it's a condo with only two exterior walls). Was thinking about their 80K unit. There is also a backup water-air HE in the air handler for a quicker shot of heat if things have been turned down for awhile. The Viesmann does come with the external reset as standard, if that helps.

    Debating the more efficient unit with the more complex electronics vs a simpler, but less expensive initial outlay. Energy costs are only going to go up and are already high in the northeast so I'm leaning towards this unit...just looking for people that may have already made the decision and their thoughts and experiences.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Like an engineer alternety's Avatar
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    I am building a house and I chose a Weil-Mclean condensing boiler with in-floor radiant and indirect DHW. I did not, and would not, consider a non-condensing boiler. Electronics tends to be quite reliable if designed properly. I do not have a concern over higher failure rates; but it could be more expensive. There are a lot of expensive electronics involved in the system control as well (22 zones, 2 slab sensors, outdoor reset).

    Your boiler should condense with the infloor, but the temperature of the water may not be high enough to perform as you want for the air handler. What you probably want to do is have the controls treat that load as DHW. That is what I am doing for the heat exchanger in the range hood make-up air system.

    From what I have seen, it appears that the Veissman is highly regarded. It is also one of the most expensive. There are also less expensive boilers that seem to be good as well.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    I looked at the Weil-McLain Ultra series, but was turned off by the aluminum heat exchanger. The stainless steel one in the Viessman seems like it should work better longer. Aluminum is the better conductor, but the Viesmann claims higher efficiency.

    When I put in the air handler, I put in whole house surge suppression (not a huge version, but not bad) and an electronic monitor for the handler itself to help protect the variable speed motor controller. Helps prevent damage from brownouts or spikes by not letting the system turn on for a delay when they occur.

    Now that the weather is getting better, it is time to take the existing system down and do something...still not sure what though.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Master Plumber Dunbar Plumbing's Avatar
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    I'm just going to make a blanket statement in regards to the topic; don't know if it helps or hinders in your case.

    My next door neighbor told me tonight that he is going to put in a electric furnace with gas backup to save on energy bills. Apparently it's the annual costs he is concerned about more than the efficiency. He's a heating and air conditioning contractor, installs new systems every day.

    Me personally I heat with gas, even though gas is very expensive I care more about the efficiency and I also know that fuel charges will go down, eventually.
    Read what the end of this sentence means.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    TVA power is some (or was anyways) of the cheapest electricity in the country. Don't know if thatis a factor where you live. In NE, we have some of the most expensive electric rates, in the order of $0.15/KWH, so that makes a difference. If I could put in a ground-sourced heat pump, I might consider it, but I can't, so it doesn't bear further research here. There was a startup company that made a splash about a co-generator plant that ended up being quite efficient in that it also created your hot water when it ran, but it was designed so it couldn't be used unless the utility power was up even though it was more than capable of generating all of the power it needed to run - ran off natural gas (thought that was kind of a shortcoming, as having a non-functioning generator there would kind of irk me in a power outage).So, I also like the efficiency of an indirect hot water tank, too. Except for electric, at >94% withthe Viessman unit, my 6' air tub could get filled up a lot faster than my tankless system now, and more efficiently. I need to make up my mind one way or the other.

    One problem is, it is hard to get a contractor to even call you back around here so getting a realistic quote on various possibilities is tough. Technically, I like the Viessman system. This model has won various awards for technical innovation, and in 2004 when it was introduced, won best of show (all categories) in a big trade show, which is impressive, too.

    Keep the thougths coming...I'm an info junky.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Like an engineer alternety's Avatar
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    Electricity is an option if you have the right rates. It can make you hot water. Prices are less volatile than other sources because they usually have to go through rate hearings with the local PUC. Oil and propane are uncontrolled (I have propane). Natural gas may not be effectively controlled.

    My buffer tank is actually an electric water heater without the heating elements. I actually thought about putting in the elements but the water connections use the holes. Electricity is cheaper than propane here.

    I thought of a ground coupled heat pump. I have, for a long time, figured that is what I would use. My concern was system reliability and the availability of service. I also was not sure it was the optimal source for DHW. I did not look at that in depth. They do produce water at the right temp for infloor radiant. They are much more expensive.

    We have fairly frequent power outages here. When I lived in the NE and midwest, some outages were in the days to weeks. With electric heat you would need a generator of larger capacity to keep resistive heat or even a heat pump running. You are essentially supplyung the fuel for heating.

    With propane (or usually natural gas) you only have to supply enough power to run the circulators and electronics. I would use natural gas if it were available. It usually is a stable supply. I have a 1000 gal propane tank and will not let it go below the minimum delivery amount (about 2/3 full I believe).

    What I would like to do eventually is put in a battery bank and inverter. This way I can run the generator periodically during an outage. The generator consumes significant propane when just ideling or running with a light load. The larger the unit the more this minimum consumption is. Using batteries the efficiency is less but probably reduces propane use for the outage.

    Propane is the most expensive fuel at this time. But, the wife wants a gas stove, the best fuel for an engine (i.e. generator) is natural gas or propane, propane does not get "stale", low temperatures do not affect it, it burns very clean in the boiler (so do modern oil burners I believe). So I have one tank for everything.

    I think condensing oil burners are scarce. I did not really look into it because I did not want oil. Even with less efficiency they are currently an economic alternative.

    As it turns out I am about to rant about energy sources.

    I don't agree with the poster above who said that prices will come down after a while. In the last few years we have turned a general dislike for the US in the countries that supply most of our oil, into outright active hatred.

    I also believe from reading some information that the long term predictions of available gas and oil is in a rather flat place in the curve and will be declining in the future. And competition for the resources are skyrocketing in China and some other countries with expanding populations and/or industrialization. There is a finite amount of oil and gas. There is an interesting possible alternate source. There are frozen nodules of methane in the ocean. But they don't know what effect any mining operations will have on the ocean and it will release yet more carbon dioxide when burned.

    Our choices are more and more going to be renewable energy sources or modern nuclear plants. Agriculturally derrived fuel does not work on any significant scale. The embedded energy (usually from petroleum) exceeds the energy produced as a fuel. We do not have enough land in the US to support a significant portion of our energy needs even if production was free.

    The hydrogen economy is generally BS. It ignores the fact that you can't mine hydrogen. It is not naturally occuring by itself. Our current choices are making it from petroleum/natural gas or electrolisis. We could do hydrogen if we had lagre amounts of the nuclear or renewable energy sources (solar, wind, tides. hydroelectric). We won't allow nukes to be built, we are taking down hydro dams for environmental improvement of the rivers, the efforts to build wind are frequently met with "you can't ruin our view", and solar is increasing but not nearly fast enough. Rather than hydrogen, which has handling and storage issues, electricity may be a better plan. A key to this would be a significant improvement in batteries or alternate electrical storage technology.

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    Agree with alternety's post re energy cost etc. that's why I want to mkae my planned house as close to energy neutral as popssible. Needless to say I think a high efficiency heating system is not only wise but essential and the "right" thing to do. Probably going with a weil McLean on my plumber's reccomendation, he is into hot water heating and i trust his judgement. he also had reservations about the aluminum heat exchanger in the Ultra series, though when he first turnem me on to that series I was seduced by it. Stepping down to a more conventioanl grade, (the GV in this case) will give nearly as great efficiency.
    I'll be using an indirect hot water tank with that, which will tie in well with a solar hot water heating system. I may use the Butler wand as that can plug right into the tank and save having a dedicated solar water tank as is usually the case with gas water heating. Just have to size the storage tank slightly higher at 80 gals.
    If I increase the solar capacity in future hope to use that for partial home heating too. I am installing radiators as they give more control than radiant heating and are therfore more energy efficient. We often turn the thermostat down low, both when out during the day and at night. Also variable occupancy of the house. Radiant flooring too slow to respond.
    I could go on about lower temps generally provided by solar water and what it implies...but won't right now. Another topic...

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    Retired Defense Industry Engineer jadnashua's Avatar
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    One of the Viessman indirects has two sets of coils specifically made for solar heating...haven't looked around, but it looked like a quality unit. Available in all stainless, too - you should never have to replace it.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    I am considering Viessman for my new house.

    I went for training in their RI facility to get familiar with the boiler. I also went in NH to see Buderus. Both firms are German. Buderus was recently acquired by Bosh. Before that Buderus (not long time ago) purchased the maker (European) of their current condensing boiler (G 142). From manufacturing point of view Viessman is really built very well. The flame is like semi sphere and appears to have a very uniform transfer of energ. The ignition system is solid. It comes with built in circulator.

    Comparing the controls (electronics), Buderus still does not have temperature reset (outside sensor). Viessman has several sensors (in and out temperature and pressure, as well as DHW sensor and outside temperature).

    Viessman works without any noise.

    The condensing boilers produce a lot of condensed water. If directed to the septic tank it is possible to kill the bacteria (Viessman offers special tank to minimize the acidity). The condense amount is significant

    I am an industrial control engineer and I do not know how to deal with eventual contractor in terms of installation, set up etc. As far as I know I cannot purchase and install the boiler myself. Any suggestions on this subject?.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Wish I could help, I'm sort of in the same position. I'm a systems engineer at Raytheon, not a plumber. I'd like to install my own, but I'll probably end up paying someone to do it as well.

    Anyone have some suggestions?
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Homeowner geniescience's Avatar
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    Jim

    A few thoughts from one info-holic to another.

    A.) What are these percentage numbers based on? Mid-80's, mid-90's. I don't know much about these products, but I do know that no heat transfer can be 97% efficient. Hope they are referring to something else. Look into this. Search on Heat Transfer, read up on the theoretical and practical limits. Then ask this wonderful company how they deemed something to be "x per cent". As you must know, statistics and percentages can lie easily. Especially percentages. Per-cent-of-what? Perhaps the manufacturer will tell you that they deemed the max attainable limit to be X and they reached 97% of that. Do all the manufacturers use the same methods to calculate their claims with?

    B.) Stainless -- what kind? Aluminum -- what kind? Stainless steel can be 304 and 316, aluminum can be anodized and purer than other kinds, etc. What are the guarantees from the manufacturers? And just to link back to the first point, perhaps the 97% numer is linked to the fact that steel is a LOUSY heat transfer agent and so the 97% refers to what might be attainable from steel, and if so, please know that aluminum is a GOOD heat transfer agent, so a smaller percent of a much better number is A-OK.

    Later I may be able to phrase all this more elegantly. Hope this helps.

    David

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    Like an engineer alternety's Avatar
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    It is a % of available energy in the fuel transfered to the water. I am not sure why you say heat transfer can not be 100%. With constrained flow alternatives and sufficient temperature differential it can get real close.

    The method in these boilers, as noted earlier in this thread, is to extract the latent heat of vaporization of the water in the exhaust gases.

    Al vs stainless - note the longevity of Al engine blocks. Have you ever had an outdoor grill with a stainless (alloy unknown but probably not great) burner. How did that work out?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The boilers in discussion here are both in the 94% AFUE range (Weil-McLain Ultra and the Viessman Vitocel). Both are modulating boilers that can throttle down to 20% of their max rating. In doing so, the highly efficient heat exchanger now has 5x the capacity, and actually increases the efficiency to around 97%. All of this requires sensors and electronics. I have faith that it works, the question is for how long, and at what costs? The WM unit uses an aluminum heat exchanger. Baring problems, agreed that AL is a decent performer, but if something did happen (a sensor fail or something) there is much less tolerance to differential heat and warping and being ruined than stainless.

    My current boiler is in the low 80% range, but I doubt it is still in that range, and has been a pain to keep going.
    The Viessman unit has won several rather impressive national awards for their design, they also seem to have a more comprehensive "system" mentality than most of the US manufacturers (although this unit is made mostly in Connecticut). The Europeans have been subject to much higher heating costs than we have for decades, and as a result spent much more research on high efficiency.

    Still looking for people with long-term experience and their thoughts.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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