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High Efficiency mod/con or natural draft?

Bill D_3
Bill D_3 Member Posts: 2
<span style="font-size:12pt">I am converting from an old oil boiler to natural gas.  The question I need help with is should I go with a high efficiency, mod/con, boiler (such as Buderus GB142/24) or a mid-efficiency, natural draft boiler (such as Burnham ES2 or Peerless MI).  This is for a 90 year old house (twin) that has about 1200 sq ft.  It has large cast iron radiators the supply and return piping is the large black pipes that seem to hold a lot of water.  I plan to have an indirect Hot Water tank attached to the boiler for the DHW.  We have had several estimates and the recommend size boiler is 80,000 to 110,000 BTU.  There is a chimney that would need a liner if we go the natural draft route.  It is possible to install PVC venting out the side wall if the Buderus is used although it would be more appealing to vent through the chimney and not have the white PVC pipes come out the side of the house.</span>

<span style="font-size:12pt">The pros for the high efficiency are lower annual energy costs and no chimney liner is required.  The cons I have heard are that the heat exchanger will go bad in about 10-15 years, the yearly maintenance is more complicated and costly, and there is more that can break and require costly repair on the high efficiency boiler.  On the other hand, with natural draft, the energy cost is higher but the annual maintenance costs are lower and the boiler is simpler so there is less that can go wrong over time.  I expect to have the house for 20+ years so I would like a boiler that has a lower cost for the long term.  </span>

<span style="font-size:12pt">Any thoughts or recommendations on what type of a system to get would be appreciated.</span>

<span style="font-size:12pt"> </span>


  • CMadatMe
    CMadatMe Member Posts: 3,086

    No brainer. Go mod/con. Would stay away from any condensing boiler with an alum hx. Would be looking at a Viessmann Vitodens 100, Triangle Prestige or Lochinvar Knight.

    You can use the chimmney as a chase. Viessmann offers a liner for the Vitodens. You would have to source from M&G or Centrotherm for the others. I've seen plenty of cast iron boilers not make it 10 yrs. As any boiler goes, maintenace and life expectancy is a result of proper sizing, proper installation and preventative maintence.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Aluminum heat exchangers...

    I wish I could see some hard data on lifetimes of aluminum vs stainless steel heat exchangers. This concern is due to the fact that I have an aluminum heat exchanger in my W-M Ultra-3 boiler. This boiler is starting its third year, so it is way too soon to come to any conclusions. But W-M has been selling Ultra boilers for at least 6 years now, so I would expect there should be some experience of failure rates vs stainless ones.

    Since I am not a heating professional, I have no basis upon which to draw any conclusions. I have looked at photographs of some stainless steel heat exchangers and I have looked at my aluminum, both photographs, and the real thing opened up for cleaning and inspection. It seems to me that the cast aluminum exchangers are much simpler to make and operate than the stainless steel ones. I do not know if the simplicity of manufacture is reflected in long-term reliability, however. As far as I can guess, the failure modes for an aluminum heat exchanger would be cracking due to lack of water or at least, lack of water flow. In a W-M Ultra boiler, it would appear that the control board would notice this an a very few seconds and turn off the fire.  You could also perhaps crack it by tightening the nuts on the cover too tightly or too unevenly, but you are supposed to use a torque wrench to tighten the nuts in a factory specified order.

    The next failure mode I could imagine would be destruction on the fire side of the exchanger. The fire side is heavy aluminum with pins (like in an old cast iron boiler). If the casting is poorly designed, those pins could overheat and burn or melt off. I assume W-M would have noticed this with their Ultra-1 boilers and corrected it very soon, so by the time the Ultra-3 came out, this problem, if it was one, would be fixed. If the fire side is not cleaned regularly (at annual inspection)  there could be other problems.

    A last failure mode could be condensation in the vent pipe running back into the boiler. It would not go directly into the heat exchanger proper, but where it does go at the bottom of the exchanger, where the condensate goes through a trap to get out of the boiler, is all a single casting, so if it rotted out, the exchanger would probably need to be replaced, unless some miracle epoxy could fix such a thing. I would not count on such a miracle.

    The third failure mode I can imagine is destruction on the water side of the exchanger. If the system had serious leaks, mineral deposits and oxygen from the make-up water could deposit on the water side, insulating the aluminum from the water. This, too, would result in destruction of the pins on the fire side. The exchanger could also dissolve from the water side if the pH of the water was too low or much too high. And since my system has cast iron circulators, copper tubing, brass fittings, and a couple of bright (stainless?) steel tubes inside the boiler, there must be some opportunity for electrolysis.
  • icesailor
    icesailor Member Posts: 7,265
    Aluminum Heat Exchangers:

    I'm not going to comment on which is better. Only that Aluminum requires a great deal more care than SS and getting someone that cares enough to properly install and service it, seems difficult. My supplier stocks everything you need to properly care for a AL HX but I see a lot of the wrong antifreeze cans around AL boilers. Aluminum works very well in air cooled aircraft engines. You see it in liquid cooled motorcycles and ATV's. Not so much now in gasoline powered automobile engines.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Not just aluminum aircraft engines

    I used to drive Alfa Romeo Giulietta Spider cars. These had an aluminum engine block and an aluminum cylinder head too (twin cam). I never had any trouble with these, even though the radiators were copper or brass. The pistons were aluminum. I do not recall, but I imagine the crank shaft and connecting rods were steel. They did have thin steel cylinder liners and steel piston rings. I think that was to deal with wear, not melting because someone in USA made car engines with aluminum blocks and no cylinder liners. The anti freeze was ethylene glycol.

    I do not have any anti-freeze in my system. I do have a caulking gun tube of Sentinal X-100 in it as specified by the boiler manufacturer.

    Since I never had a non aluminum mod con, or any other mod con for that matter, other than what I have now, I do not know what a pre-season start up should take with a stainless heat exchanger. It seemed to me that the pre-season service would take about 2 hours, and that is what it takes. That includes lots of little things,, checking pH of the water,  and the high labor item is removing the side of the heat exchanger, cleaning everything, examining and cleaning the condensate trap, replacing the high voltage electrozapper ignitor and all the related gaskets. Now it seems to me that for a stainless hx, it would take about the same amount of time. I have no idea how to clean the fire side of one of those heat exchangers.

    My former contractor allowed 15 minutes for this, hence the status of former. The turkey they sent did not even know if I had an oil or a gas burner, though that was obvious: no oil filter and a gas pipe coming down from the ceiling with that little T and capped nipple to collect water and crud -- I have never seen that on oil systems.

    The hardest thing still remains to get them to bring along a digital combustion analyzer and know how to use it. Since I never had one of those, I am not sure how long a combustion test would take (there is a hole in the vent where you are supposed to put the combustion analyzer probe; the hole is normally for the exhaust temperature sensor). I do not think it would take more than a few minutes, provided everything was OK and nothing needed fixing or adjusting.

    Is an annual startup that much faster for stainless heat exchangers? Or is it really true as my former contractor said that gas boilers do not need annual maintenance? (Not a serious question.)
  • Tim McElwain
    Tim McElwain Member Posts: 4,524
    Truth from someone

    who has been at this for over 60 years gas has always required annual maintenance and inspection along with a combustion test if for no other reason to make sure no high levels of carbon monoxide are present.

    Granted it may not take as long as oil (that depends by the way).

    Anyone installing gas equipment should also be responsible for the life of the equipment to service the equipment, do annual maintenance and conduct a combustion test. They also should be well paid to do so provided they know what they are doing.

    The problem is good service techs are few and far between. That is why warm air systems tend to get better service as most HVAC techs are better servicemen. That is based on me teaching everyone in the business and getting a pretty good handle on who is the most professional. My own preference is a good oil service man makes a great gas tech. Why? They do combustion testing, they understand wiring and they are not afraid to get dirty.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Is it just my neighborhood?

    "Anyone installing gas equipment should also be responsible for the life

    of the equipment to service the equipment, do annual maintenance and

    conduct a combustion test. They also should be well paid to do so

    provided they know what they are doing."

    When I bought this house it had an oil fired GE boiler with the original GE oil burner in it from the early 1950s. I kept the heating oil supplier the former owner used. In about 10 years, as far as I can tell, they never did a combustion test. They measured the "efficiency" by measuring the temperature of the exhaust going up the stack. they did this only once or twice.

    After a while, the burner started leaking oil over the floor, so the replaced it with a Beckett oil burner.  Each year for service, they replaced the nozzle and the oil filter. That was it. Once they could not get the right color flame and pulled the burner out, and examined the combustion chamber. It was full of crap; piles of powder and chunks of stuff. They cleaned it all out, put it back together, and got the right color flame. It seemed to me they should have done that cleaning more than once in 30 years. Still no combustion analyzer.

    When I replaced all that with gas, the new contractor did not do a combustion test. I asked why, and they said the boilers came set up correctly from the factory. At the first service, they still would not do a combustion test, and they would not open the heat exchanger as required by the installation and operation manual. I tried to complain, but got nowhere. So I switched contractors again.

    I have never quibbled about price. I just want the contractor to at least follow the requirements of the boiler manufacturer. My new contractor even wrote me a custom contract that said they would follow W-M's procedures exactly. Well, they are a lot better, but now I am now starting my third year (completed two winters) and still no combustion test. See why I am considering getting a combustion analyzer? It does not make sense. I mean, how often will I run a combustion test? Once or twice a year? And every couple of years I would have to replace the sensors? And if the analyzer detects a problem, I do not feel I should be the one to adjust the gas valve mixture, though from the manual it looks pretty easy.
  • Tim McElwain
    Tim McElwain Member Posts: 4,524
    This is why

    the Mod-Con boiler market will eventually disappear. Poor service will put you out of business every time. Very few service companies carry combustion test equipment. When I make emphasis of this in class they have all kinds of excuses why they will not get involved with combustion testing.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Not soon enough.

    "Poor service will put you out of business every time."

    Maybe it will eventually, but not soon enough.  I had oil heat from 1976 until 2009, with two companies -- two because one bought out the other. NEVER in 30 years did they ever run a combustion test. THey could replace nozzles and oil filters. They also replaced ignition transformers too. The replacement contractor is still in business.

    I wonder if Tools-R-US rents out combustion analyzers in good condition.

    If we are to  continue to burn stuff to get heat, it seems to me a shame for mod-con boilers to disappear because of incompetant servicing. It seems to me that manufacturers should be far more diligent in ensuring their installing contractors install correctly and maintain properly.
  • Tim McElwain
    Tim McElwain Member Posts: 4,524
    The problem is

    the training in many cases is done at a hotel with lunch and beer after. The presentations are often sales oriented. This does not train anyone.

    Do not get me wrong some offer factory schools which you go and stay at a hotel and attend classes in their factory training facility. Most of these are very good and do at least get some hands on accomplished.

    The problem is training on the fundamentals. Most plumbing and heating contractors know very little about combustion, controls, electronics and modern day venting issues. It takes at least a week of training just to get the fundamentals under their belt. Then they should attend training on each individual boiler or furnace. It takes a definite commitment along with some good training institutes along the way.

    By the way I would not purchase a combustion analyzer. Search for a good company that will give you what you want in the way of service.
  • Greg Maxwell
    Greg Maxwell Member Posts: 212
    Boiler replacement

    In my opinion, people are paying way to much attention to these "mod-con" style boilers. They all make claims of 95% efficiency, but no one reads the fine print where it says "up to" 95%. In all likelyhood, you will AVERAGE somewhere in the 88-90% range. And, you will have a boiler with a 10 year warranty. Propane is about 93,000 btu, natural gas will be approximately 100,000, and oil is 140,000. I would go to a mid mass cast iron boiler, and not atmospheric. You are going with an indirect, so a boiler such as a Biasi SG will give you (in oil) about 87% AFUE. Put a gas burner on it if you wish, but you will lose 4-5% AFUE. You will have a boiler with a lifetime warranty. We have had plenty of calls this year where people were very dissapointed with the performance of those very expensive wall hung gas boilers, and while we do sell them, its only after explaining the difference to the customer, then if they still want it, here you go, but you may not get the fuel savings you had planned.

    Then take a look at the system. What is the heat load of the building? What is the btu output of the terminal units? Put some research into outdoor reset, modulating water temperature and possibly zone syncronization. THAT is where the the real savings, and comfort will be. Then, you will have an excellent system. Great boiler efficiency, and great system efficiency, AND a lifetime warranty.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Some Disagreement

    Been away and tied up for a while. Nice to be back..

    I have to disagree with you that it's the boiler that is the culprit in jobs where consumers feel they didn't get what they paid for. I also disagree that to flat our state all mod/cons are a 10yr boiler.  I do agree with your evaluation of the efficiences of mod/cons and the results provided from a good system side design.

    Most jobs I see where consumers are not happy with the results come from a poor choice on their part with the picking of the contractor to do the install. You find that 99 percent of these jobs were installed without a heat loss, proper radiation survey and design by the installing contractor. To throw the boiler as the culprit is just not true.

    I can state with confidence thru real job installations that a properly, sized and installed condensing boiler will save a consumer between 30-50%. Your looking at AFUE only. A condensing boiler isn't firing at its max rate every day like as the power burner on that cast boiler is. To use AFUE as your means of showing the difference in savings also isn't a fair and correct comparision. I may only be using 35% of the condensing boilers load on some days where you are still using 100% of the load. So now which burns more, a condensing boiler firing at 50,000 btu's at 88% AFUE or that power burner firing 100,000 btus at 87%?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    no one reads the fine print

    I read the fine print. As you say, you do not automatically get the highest effeciency that the marketeers can dream up. For my boiler, they claimed 93% AFUE, though they did not say what return temperature was required to get that level of efficeincy. For newer models, they claim up to 96% I believe. If I look at the graph in John Siegenthaler's book, third edition, page 60, I see I would need return water temperatures of 110F or less to get that efficiency.

    Now it happens that my largest heating zone in in-slab radiant and I have the outdoor reset curve for that zone to supply water between 75F and 120F depending on the outdoor temperature. Surely the return water temperature is less than the supply. Furthermore, the supply temperature to that zone does not get up to 120F until it gets down to 6F outdoors, and I have never seen it that cold. Design temperature is 14F around here. On design day, the supply temperature is 112F. So chances are that I do get 93% for that zone down to design temperature, and it runs in condensing mode all the time for that zone.

    The other zone requires much less heat, but it is heated by baseboard. That zone gets water supplied at between 110F and 134F. So I may not get 93% out of that zone, but it will condense at least partially until it gets down to design day. Since that zone requires only about 1/4 the heat of the other zone, it probably does not matter all that much.

    My conclusion is that you can get efficiencies similar to what is claimed, provided you system is designed to run at condensing temperatures. If not, you would have to change your heat emitters so you could run at lower return temperatures (if practical) or use, as you say, the bestcast iron boiler you can get.

    "you will have a boiler with a 10 year warranty."

    I believe mine comes with a limited 15-year warranty on the heat exchanger. It is covered at 100% up to 10 years, decreasing to nothing in the 16th year.
  • Henry
    Henry Member Posts: 995
    Mod-con forever

    For commercial installs, we only recommend mod-con. Small residential do not consume unoff to make the expense worthwhile! Without looking at claimed efficiencies, it is all in the install and micro management of the heating load according to heat loss! Anyone can basicaly hook up a boiler. The difference between one install and another is the way the boiler is connected and managed.

    In the little residential, the Raypack Residential line is hard to beat. We have saved certain customers up to 50% with these atmospheric boilers! 6 units and up apartment blocks will be mod-con. We did 9 blocks of 7 apartment each with mod-con and condensing hot water tanks (client request). The savings were between 35 and 55% on steel convectors and regular HWT gas fired.
  • Steamhead
    Steamhead Member Posts: 15,637
    Some Giannoni-based mod-cons

    have only lasted five years. They might still be under partial warranty at that point, but with most the owner still has to pay for labor. And they all remember how their old boiler lasted more than 20 years.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • AFred
    AFred Member Posts: 81
    My vote is on the burnham

    You won't need to get to know your serviceman as well if you stick with the natural draft.

    Look into the ES2, think about adding the outdoor reset. Very ez to add an indirect to it.

  • CMadatMe
    CMadatMe Member Posts: 3,086
    No Way

    I wouldn't go the ES2 route. Its a great boiler but once you line the chimmney, add the ODR and LWCO card you are at the price of a condensing boiler. While I'll contend that you will not be condesning all the time and most likely will see efficiencies 88-92% its the modulation rate that picks up the fuel savings. You cannot look at AFUE alone. The ES2 or any other non modulating piece of equipment whether providing outdoor rest or not cannot match the overall savings over the life of the equipment. Some will say maintenace offsets the cost and I disagree with that too. The cost of keeping any piece of equipment operating at its fullest efficiency out wieghs the money spen on not maintaining a piece of equipment. Does a Mercedes require an oil change any different from a Focus? All equipment should be maintained yearly.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Tim McElwain
    Tim McElwain Member Posts: 4,524
    The ES2 with

    the Honeywell S9360 Series Integrated Control (Burnham calls it their IQ Control System) the IQ Option Panel resides below the S9360 control. This system is no easier or harder than a standard Mod/Con control system so if you are spending the money look at the pros and cons of both. Everything today is going electronic so even the low end packages are electronic. The ES2 is 85.!% efficient .

    The Weil McLain GV90 is still the same package electronically as the standard series 4 Gold, they have just added a recuperator to the basic boiler package. The recuperator is a stainless steel heat exchanger that increases boiler efficiency by extracting additional heat from the flue gases. Return water passes through the recuperator before entering the boiler. What I used to call a heat reclaimer. They claim 92% efficiency without Modulating Or directly condensing in the boiler.

    The truth is Mod/Con gives you more bang for the buck even though longevity with some units is an issue. There are some if properly maintained may give 20 years. There have been boilers such as Hydro-Pulse and others of that era that when maintained are still running. It all comes down to a good install and follow up service by the guy who put it in. That should be a law by the way.
  • Greg Maxwell
    Greg Maxwell Member Posts: 212
    Boiler Replacement

    The problem with "mod-con" style boilers is that most are sold under the premise that they ARE more efficient than oil. Do the math. 40% more propane to create the same BTU's as oil. Look it up. There are charts that will show you the $$$ it will take for each fuel to create 1,000,000 BTU's. Most, at least the ones I see, are retrofit. They are put into homes with baseboard, and many small zones, that are designed, (if someone took the time back then), for 180-200 high limit. You cant get a low enough return water temp in that type of system to condense. The things will never get a chance to reach steady state efficiency. With 1/2 gal of water in the heat exchangers they come on, and hit high limit, then shut off. The zone continues to call, then the process starts again. Even on low fire, with the water content they have, the boilers are too large for the smallest zone. You have short cycling. You use more fuel. What does that do for efficiency. The best you can do under those circumstances, is use a buffer tank to add volume to the system. Theres another $$$. Where is the savings when you have spent $$$ more on the equipment, then more $$$ on fuel. Yes, they can be efficient if all the water temp criteria are met, but be realistic. How often does that happen on retrofit. You have to design the system with that type of boiler in mind.  Also, the claims of up to 95% AFUE efficiency ARE based on AFUE. Thats a manufacturer claim.

     Dont throw out those mid mass C/I boilers. With outdoor reset, they are efficient. Set the heating curve properly, and even those baseboard systems will operate well for years. Long after that wall hung boiler has had to replaced, the cast boiler will be continuing to give you savings. In the long run, I believe they are the best choice.
  • Greg Maxwell
    Greg Maxwell Member Posts: 212
    "mod-con" warranty


    What do you think it would take to replace your heat exchanger in 10yrs if it goes? Remember, it is only the heat exchanger that is covered for that length of time, not the boiler. I bet you would opt to add the extra cost of a new boiler at that time. Mose people do.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    edited June 2011
    What would take to replace your heat exchanger in 10yrs

    If you mean just inside the 10-year window, it would cost me the labor. If you mean a day after the 10 years, it would cost me the elabor and 20% of the cost of a new heat exchanger.

    " Remember, it is only the heat exchanger that is covered for that length of time, not the boiler."

    I remember. There are two warranties for the rest of the boiler. There is a 100% warranty for the first year (now expired) and another 5-year warranty that I cannot find at the moment.

    Just found it. 100% of parts and labor for the first 5 years

    I do not know what I would actually do at that time. I guess it would depend on my finances at the time. On the one hand the heat exchanger is most of the boiler. Other than some pipe, some wire, and the U-control board, what there is is a gas valve, the burner, a variable-speed blower, and the igniter. They seem to replace the igniter each annual service anyway. The burner is like a tin can with lots of tiny holes in it. Other thean burning or clogging, there is not much to go wrong with it. My guess is that the most likely thing, other than the heat exchanger, to quit would be the variable speed blower or possibly the gas valve. While these might be expensive, I imagine they are cheapre than a heat exchanger and the labor to replace it.

    I have had this boiler a little over 2 years now, and two heating seasons. I have watched the annual servicd being done, so i have a fairly good idea as to the time required to do some of these things. I know the cost of some of the items. If lightning struck and took out hte whole boiler, I know what I would have to do. In the two years I have had it they already have a newer more efficient model. As far as I can tell, this involves a bigger heat exchanger. So in 10 years, if something expensive enough happened to this boiler, it might well make sense to replace rather than repair. It would depend on the costs as they were at the time and the finances remaining to me by then.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited June 2011
    That's Not A Boiler Issue

    That's a contractor issue. Why is the boiler to blame for poor sizing, design and installation? I'll say it again, a properly sized, designed, installed and maintained mod/con will provide considerable savings over a 85% cast boiler and provide the longevity. You seem to be leaving out in your arguments that your boiler is firing at 100% on every fire and I'm modulating day in and day out. Your also leaving out that if my boiler short cycles what do you think yours is doing. I have a much better chance of making mine not then you do without the need of a buffer tank.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Efficiency, etc.

    While your numbers may be correct, you present them in a very confusing manner. I looked up a table of prices afor various fuels and got this:

    All of the following fuels are equivalent to 1,000,000 Btu’s
    1. Electricity 293.083 kWh (3412 Btu/kWh)
    2. Natural Gas: 1 MCF, 10 therms or 1,000 cubic feet
    3. Coal: 83.34 pounds @ 12,000 Btu/pound
    4. Propane 10.917 gallons @ 91,000 Btu/gallon
    5. Gasoline 8.0 gallons @125,000 Btu/gallon
    6. Fuel Oil #2 7.194 gallons @ 139,000 Btu/gallon
    7. Fuel Oil #6 6.67 gallons @ 150,000 Btu/gallon
    8. Wood 285.7 pounds @ 3,500 Btu/pound
    For liquid fuels, the BTU/gallon are different, but since they are not the same price per gallon, that does not matter unless you are restricted to a certain size tank. Even in that case, I do not know how many home owners would wish to burn #6 heating oil. What matters is BTU per dollar.  For me, I just paid $2.5936/therm, but that is mostly the the customer charge as I am just heating domestic hot water at the moment. Gas $4.66, delivery $3.30, customer charge $8.25. I have not bought #2 heating oil in several years, but back then it was about the same price as gasoline around here.

    When I had a mod-con put into my house, it was a retro-fit.  I could certainly get high efficiency from my downstairs zone that is radiant in slab; since the supply temperature never exceeded 120F, and was usually less than that, efficiency for that zone was very good in any case. The other zone was baseboard and it was too small at that. I calculated how much baseboard I would need to heat that zone at condensing temperatures, and replaced the undesized baseboard with enough so I would get at least some condensing even on design day. It is a small zone, so I had to adjust the reset curves, the differential setting, maximum firing rate, etc., for the reset for that zone to reduce cycling rate, but I could do that.
  • gennady
    gennady Member Posts: 839
    This is why

    I cannot agree to that. I would say, the companies which will keep ignoring mod/con market will go away , and new companies, which will accept products customers want, and its service requirements, will make good. Progress cannot be stopped.
  • gennady
    gennady Member Posts: 839
    edited July 2011

    It seems that there is a confusion in terms, AFUE is meaningless number. During my combustion tests, i get around 88-89% combustion efficiency on mod con boilers, and if it is condensing fully or partially, from 3 to 11% additional efficiency due to latent heat of vapor condensation in exhaust gases. The key is in the whole system setup, not a boiler efficiency. Put properly sized and installed mod con boiler in cruise control mode(city and highway mpg in cars as an analogy), and you will cut heating bill 50% and up. (way up)
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