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Another Boiler Replacement Question!

Another boiler replacement question. I know everyone has seen these before but I thought I would ask for anyone with past experiences. I am looking to possibly replace the hot water boiler in my 1925 house that has rads. The boiler is a 1980's vintage Burnam cast iron at 69% eff. No vent damper. Complete heat loss calcs that were performed indicate that the boiler was correctly sized. I am woking with my local supplier and heating guy. No one is sure what would be the best option.

Is replacing the boiler with a new mod con the best option for energy savings or would the fact that the house has radiators negate some of the value of the condensing aspect?

Would I be better off with just a modulating boiler such as a Larrs Endurance with no condensing feature?

Would just installing a newer more efficient basic boiler (not mod con) be a better option?

Or would I be better off just adding a vent damper and outdoor reset control to the existing boiler to increase efficiency?

House is unfortunately insulated as well as can be. It is constructed of structural clay tile walls with brick veneer exterior and plaster applied directly over interior. (No effective way to insulate) Newer double insulated windows and better attic insulation have been installed. Doing everything I can to better insulate and seal. Last winter was first in house and had $450 natural gas bills for a few months for a approx. 2,000 sq. ft. house set at 62 degrees. ( Maybe this is not bad compared to what others have posted)

Did I mention that house has small chimney flues and installation of a liner might be difficult.

Any experience or help would be appreciated.


  • Al Letellier_9
    Al Letellier_9 Member Posts: 929
    conversion to new boiler

    Hard to answer directly without seeing the setup up close and personal, but the more efficient the boiler you can afford, the better. Fuel of any kind is not likely to get cheaper in the years to come. I would think a mo/condensing boiler set up primary secondary, with outdoor reset and and indirect water heater would be the way to go, based on the info you provide. Many options are available as to controlling the system, and your heat guy should know that.....if not, maybe he's not the right guy for the job.

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  • J.C.A._3
    J.C.A._3 Member Posts: 2,981
    You've got....

    The perfect setup for a mod/con boiler ! The bigger the delta T, the better the condensing boiler will perform.

    I would see if piping TRV's into the system is a possibility. With these 2 upgrades,(piping permitting,) you can achieve the best comfort, and the most savings.

    In any case, the mod/con boiler will help you achieve better fuel use numbers, but effeciency comes with much more than a boiler. The system is a bigger criteria in determining the "overall savings".

    Go for it. Chris

  • Thanks for the reply. I guess what is also important is ultimate payback in energy savings. I too am concerned about energy usage and want to do what I can to reduce consumption but will a mod con payback in a reasonable time frame verses other options? I think this is what stumps suppliers and installers.

  • Thank you for the info Chris. I never really noticed one room being too hot or cold. I have never adjusted the supply valves at any of the rads. I guess its possible that some rads could be oversized but keeping temp down at 62 last winter it was hard to tell. You think thermostatic rad valves would help that much? Also tech person for muchkin boiler didn't think this was best application for mod con. I am inclined to agree with you though. Mike
  • J.C.A._3
    J.C.A._3 Member Posts: 2,981
    As the price of fuel rises...

    The payback comes in a shorter time. Unless there is someone out there who knows anything different...I'm betting that the price of ANY fuel will only be going one way...north on the map.

    The time for payback IS important, but your footprint on the use of resources becomes smaller....so you win.

    Great show on History Channel the other night about renewable energy . The claims are probably a bit overblown...but if everyone did just a bit more of their part, I believe that they will be achievable in short order. (as long as the usual suspects will be able to keep their profit margines, and investors happy. TRUST ME..THEY WILL BE VESTED WHEN IT HAPPENS!!) Chris
  • mel rowe
    mel rowe Member Posts: 324

    Just curious about the boiler sizing issue. During the coldest days of the winter, what % of the time is the boiler running to achieve the temperature you want in the house?

  • Thanks, I thought I had a copy of the heat loss calcs with me but I don't at this time. Calcs seem to indicate that the existing Burham P205W 130,000 btu input, DOE 108,000 is close. The boiler seems to run a lot but I think at times in shorter cycles than it should. Mike
  • mel rowe
    mel rowe Member Posts: 324

    Mike, I am a homeowner with a lot of curiousity about steam boiler systems. I know that everything you read says that you should fire to the connected load; however, the connected load (radiators) were all sized and installed back when there was little to no insulation in old houses and lots of people liked to open windows at night. When my boiler was replaced 17 years ago, I'm sure that they just put in the same capacity as the old one. When I measure the EDR of all my rads and compare to the boiler capacity, it appears that it is 30 % undersized; however on the coldest day of the year, it only runs about 30% of the time. Of course I have addded thermal windows, foam in the attic, and foam in the walls. I have a friend that with similar circumstances, his boiler appears to be undersized by 50%, yet he has no heating problems at all. I know the safest aproach is to oversize, but with fuel bills as they are and will be, I suggest you question very hard, why you need boiler capacity that might be excessive. By the way, spraying foam into the walls through holes drilled in the mortar, is easy and very effective.

  • I will check heat loss calcs again which also looked at rad sections and sizes. Streuctural clay tile is not the easiest to try to foam fill. Hard to drill an cores don't all line up by course. Still may be possible to drill through mortar joints in brick to get to tile but will take many holes. Thanks, Mike
  • mel rowe
    mel rowe Member Posts: 324

    Not to belabor the point, but can someone explain how heat loss calculations are done? I'd really like to understand what they are based on.
  • Weezbo
    Weezbo Member Posts: 6,232
    basically they are based on maintaining a specific temp

    in a location within your home or building on a day that is considered cold in you R neck of the woods.


    the how to part is made simple these days with small specific computer programs. one minor technicality is that computers are not engineers ....you yourself may need to check certain aspects by an actual site visit ..especially when it is a building that is already in existence. the selection of materials in new construction and the veritable application can indeed make a definite one heck of a difference... to get two viewpoints or three opinions or seek the wisdom of council in difficult undertakings is a good principal to follow.

    there are different aspects to heat loss and as the controls or control strategies of whole house systems becomes more widely accepted we may see some modest changes in improvement over previous calculations.

    predicting the weather is not one of my Forte`s because there can be major variations in wind and a variety of other minor technicalities before you designe something that under preforms or is wasting materials it is important to basically get up off that thing and cop a visual.

    some things i think will be built in to new control systems will be able to make changes based on control sensors that are fed a variety of information including Satellite information . it may also be smart to suggest more than one heat source or auxillary source when you have a say or can he heard. new appliances in the future may also utilise advantages basically already there just modified a bit to meet heat loss. like Brad says there is quite a bit more to it than using square foot times X btu's ...those are something of a guess at best.

  • mel rowe
    mel rowe Member Posts: 324

    How would you use that kind of info to determine the boiler capacity needed? thanks.
  • Brad White_125
    Brad White_125 Member Posts: 28
    A * u * Delta T

    Area in square feet times the "u" factor times the Delta-T in degrees F. for every surface separating heated from non-heated space.

    The area is just that, HxW or LxW.

    The "u" factor is the inverse of the R factor for the entire wall assembly. Typical 2x4 insulated frame construction will be about 0.075 to 0.09 depending on framing percentage. 2x6 insulated construction might be 0.05 to 0.06 by comparison. An R-30 roof would be 0.033 as examples. Double-pane standard glass might be 0.6 to 0.7. Low E maybe half that at center of glass, 0.42 or so overall. Just some ideas.

    The temperature difference is typically the indoor temperature minus the design outdoor temperature for your area. Here in Boston the 1% temperature is 7 degrees although away from the coast most use zero. So if you have a +2 outdoor design and want to maintain 68 degrees, you have a delta-T of 66 degrees F.

    That is transmission....

    THEN you have to add in infiltration, air leakage in and out, a study in itself. Typically a CFM of air leaking in (and hence out) will impose a heat loss of (CFM x 1.085 x Delta-T)

    Short primer.... way too long to explain in detail. If I can, I will rustle up a copy of an essay I wrote for my students....
  • Timco
    Timco Member Posts: 3,040

    Another quick question on the subject. When replacing an existing boiler (hw) on an existing system, and the house heated well, can the new boiler be sized in any way to the load you know you have (existing rads) or will a new heatloss need to be performed? Understanding the old snowman was way oversized, one wold think these would be a way to size to the load. I know this is true for steam, but how about hw?


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    Just a guy running some pipes.
  • Ron Schroeder
    Ron Schroeder Member Posts: 998

    once you make all the measurments and calculations, you take that answer in BTUs and match those BTU per hour to the BTU output of a boiler, furnace or other heating plant
  • mel rowe
    mel rowe Member Posts: 324

    When I look at the numbers on my boiler, I see input of 299,000 btu, DOE heating capacity 243000, 760 sq. ft. of steam, and 182,300 output capacity. I am a little confused as to the difference between the 243000 and the 182,300, which I know corresponds to the 760. Would someone kindly explain.
  • Rollie Peck
    Rollie Peck Member Posts: 47
    Boiler replacement options

    What some people have done with houses built like yours
    is to put foam boards on the outside of the house and then
    cover them with siding. This is not cheap, of course, but it
    puts all that mass of masonry on the inside of your
    insulation, causing the inside temperatures to be very stable.

    Rollie Peck

  • Brad White_125
    Brad White_125 Member Posts: 28
    Boiler Ratings


    The input is just that, BTU's in per hour. (299,000 is a neat way to stay below the 300,000 limit whereby more commercial code reqirements are triggered).

    The DOE (Department of Energy) indicates a combustion efficiency (if not stated as AFUE) of 81% (243,000/299,000).

    The DOE number is more reflective of what your boiler will do once warmed up and steady-state (and all other things in balance such as radiation and outdoor temperatures.. Never happens! :)

    The 182,300 is most likely the Net I=B=R output which extracts another assumed 33% for piping and pick-up, from your DOE gross output. (243,000/1.33 = 182,700 pretty close!)

    The 760 SF of steam is the maximum amount of connected net radiation you can serve with this boiler. At 240 BTUH per EDR, this corresponds to 182,400 BTUH. Again, close enough...

    So, if your radiation totals 700 SF you are good. If it totals 800 you are a tad over but if the piping is well insulated (using your 33% margin here) you may get by. This is just to illustrate, not to size the situation for you! I have not seen it so cannot responsibly give a definite answer for you. Just a guideline.

    Hope this helps!

  • Ken_40
    Ken_40 Member Posts: 1,320
    JCA's correct!

    Your existing radiation would L-O-V-E a mod-con.

    Can't you almost hear the voices singing (;-o)
  • mel rowe
    mel rowe Member Posts: 324

    Brad, by my calculations my rads add up to 970 EDR. Since my boiler shows 760 sz. ft. of steam, This is why I said that it would appear that my boiler is 20% undersized; however, the boiler only runs about 30% of the time, on the coldest days. My only explanation for this is that the rads were oversized originally, plus I've added a lot of insulation in the walls and the attic, plus thermal windows. A friend of mine has the same experience with his boiler. So all of this seems to say that in determining the size of a new boiler, you can't just go by the EDR for the rads, or you'll end up oversized and fuel inefficient.
  • Brad White_125
    Brad White_125 Member Posts: 28
    Interesting, Mel

    Is the house heating well and do the radiators get uniformly hot all the way across? Especially the remote ones?

    If that is the case then your net I=B=R output is being used, especially if the piping is insulated. It also may be that you have over-estimated your EDR?

    It may also be your perception of running 30% of the time: Steam boilers by their nature cycle based on pressure and that is related to the condensing rate (of course!). So your insulated piping moreso that the envelope will have an effect.

    That the walls may be insulated helps the overall heat loss but not the ability of the boiler to fill those (by now over-sized) radiators.

    The true proper way to gain economy by insulating a house with a steam system is to reduce the radiation in each room proportional to the actual new heat loss. This way your boiler, properly sized to match the now-reduced radiation, can be nicely sized.

    If you have too much radiation and the boiler to support it, yes, I can see cycling as you state and that may be the condition you describe.

    The steam output and the radiator/system volume is incontrovertable. No benefit in having too much radiation because the heating medium is at a given and relatively constant temperature (212-215 degrees F.

    Unlike water systems where the additional EDR will allow lower water temperatures.
  • mel rowe
    mel rowe Member Posts: 324

    Brad, thanks for your response. This is a very interesting topic. To answer some of your questions, I am pretty confident of my radiator EDR calculations. The house is heating very well, especially now with my new dropped header and additional tapping into the boiler. The system easily pushes steam to the most remote rad. All the rads do not get hot all the way across, because on most of them I have installed TRV's instead of normal vent valves. I have adjusted the heat anticipator on the thermostat so that it remains on long enough to get the last rad hot and shut off right after the pressurtrol sees 1.5 psig for the first time. So there is no cycling going on. The boiler just runs for about 20-25 minutes and then shuts off for 40-50 minutes. I guess I've reduced the radiation in my house by using the TRV's instead of trying to downsize all the radiators. With these conditions, I do have an interest in whether there might be some advantage to trying to further reduce the steam velocity by downfiring the boiler some. Might this be worth pursuing, since it might also keep the boiler running longer, which I understand might be more efficient.
  • Brad White_125
    Brad White_125 Member Posts: 28
    Mel, it seems

    as if you are doing well! That the boiler runs x-time and it coasts well between and the house heats, what's not to like? Your use of TRV's seem to have bought you the margin you need. I have not studied the comparison/trade-off between TRV's and EDR margins.

    As for downfiring, you would have to weigh the lower input over anticipated time. I mean, if you are making the setpoint in a reasonable time (20-25 minutes) burning 2.0 GPH, that will consume 0.67 to 0.83 gallons.

    If you decrease the input it increases the time. Will it do so efficiently? Will the longer time mean the same, less or more oil? Too many variables. But I would explore reducing the firing rate to the least consistent with the boiler recommendation. You have to protect your investment.

    Remember, the most energy saved is when the burner is "off".
  • GW
    GW Member Posts: 4,609
    is there two conversations going on?

    Mike, I do lots of boiler swaps. That's a bummer your contractor/vendor can't get excited about what's best. I didn't read all the posts word for word, but are you saying it's hot water cast iron rads? I practically start drooling when I get into those jobs. FWIW and FYI, I would pay more consideration to the "system" than the "boiler". I didn't say buy a cheap boiler, I'm saying buy a boiler/control system that will let your heating "system" run the circulator 24/7. TRV's are great because invariably no radiator is sized precisely for the given room it's in, so the TRV will "fine tune" the heating requirements (added comfort and possibly better fuel savings). IF you choose to employ an indoor sensor, a.k.a. room temperature feedback, you DO NOT want a TRV in that particular room. For goodness sakes don't have a typical thermostat installed, even set back thermostats. It's rather exhausting explaining how to manipulate the system to react to various parameters, but to keep it simple, and IF you have TRVs installed, just skip the indoor sensor and fine tune the reset curve by trial and error (tweak it down until the house doesn't keep you cozy, then inch it back up to where it does keep you cozy).

    It seems like you paid through the nose for 62*, OUCH! I have a hunch if you find a good heating guy who knows this stuff, and if fuel costs about the same as it did last year, you may be able to heat your house at 68-70 for similar fuel costs; perhaps less if you can deal with some of your home envelope issues.

    We do a fair amount of Viessmann, Buderus, and Munchkin boilers. Just find a guy you can work with and go with his brand, as long as he knows this constant circ stuff!

    Oh, I almost forgot to comment on "sizing for the load it's attached to". Did someone get confused and start talking steam? Two different beasts, two different topics. I get all giggly inside when I cut the BTU in the heat/hot water BTU in HALF! It doesn't happen all the time, but on one recent job I recall we yanked a 120,000 BTU warm air furnace (gas) and a cheap gas hot water heater rated at 40,000. We installed an 80,000 BTU Munchkin with an air handler and super stor and everything was great!


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    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • Brad White_125
    Brad White_125 Member Posts: 28
    You know, Gary

    I am probably as guilty as anyone! I just responded to Mel's question without regard for the prior discussion- an inadvertant hijack! I think this one went to Cuba. I will be more careful in the future.. Sorry!

  • mel rowe
    mel rowe Member Posts: 324

    Brad, thanks very much for your time and info. I guess with all that I have learned from the Wallies, and installed on my boiler to correct initial installation defeciencies, it is working very well currently. And I know the old saying that if it "ain't broke don't fix it", but the many questions on the board about sizing replacement boilers, plus my own experience here, makes me wonder what I would do if I had to buy a new boiler. I tend to think I would buy a smaller one next time around. Maybe I misunderstand, but it seems to me that the ideal situation would be to have dry steam, a balanced system, and boiler capacity that would just stay ahead of the heat requirements on the coldest day you might encounter, while running almost all the time. Wouldn't this be the most efficient system you could have??????
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