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Wanted: Hydronic Load Calc & More. modcon sizing

mknmike Member Posts: 16
edited January 20 in Radiant Heating
I’m considering buying a TriangleTube for my latest purchased home, and want to figure out what size.  Since I’m going with a modcon, my gut tells me it’s ok to oversize it.  Perhaps if flow rates are higher with the three pump/zone system, lower temperatures (more condensing) would occur.  I don’t know.  

The 1919 house (I don’t live in) currently is capable of cooking the place up with 190 degree water in short order and will have you sweating on that 55-60 degree day if you aren’t careful.  This just can’t possibly be efficient.   

I live (in the same neighborhood) in a 1929 built twin (connected on one side) ~2500 sq ft 3 story with a few 2-3” pipes nearly all wrapped in insulation in the basement before heading to original standing radiators.  Attic is 4th floor well insulated.  Walls have no insulation but are plaster over double brick.  My single-taco pump TriangleTube Solo 110 is set to a curve of:

outside temp + water temp = 150 F

Nice and simple.  It might not heat real fast when coming home from a trip, but it’s not really that bad.  I like to start fires on the coldest of days too, figuring that’s when we get the most heat out of our fireplace insert.  I think our gas bills rarely exceed $100/month whereas we might have burnt through well over 100 gallons of oil / month generally requiring more than two 275 gallon tanks per year.  The TT modcon is great.  I never added a water heater because our water heater was brand new when we got the TT.  So it’s capable of running really low temps.  Our water heater is probably terribly inefficient though.  

Back to the subject property:

We bought this 1919 (in same neighborhood) 4200 sq ft standalone house this past summer and are renting it out.  It’s got a gas cold start (bang bang?) boiler and two water heaters under the fireplace (was on porch wall that got enclosed and turned into an addition).  It might be a long run to get PVC outside, but we can do it.  It’s got 4” (or possibly 5”?) boiler pipes in the basement that I confused for sewer pipes with no insulation.  I wonder if this house was originally a steam boiler setup.  The heater went straight to 190 F when we fired it up.  The first floor of the house was converted to cast iron baseboard from the original standing radiators.  We are investing in this house, and I figure updating to a modcon is in the works.  I like triangle tube (30 miles from me, and I can drive there for parts if needed) and heard a horror story of a neighbor with a Weil McLein.  So I’m shopping for a TT again for our new purchase.  (Our current TT hasn’t needed ANY maintenance in ~10 years of service now.)

Looking for advice on what to do next.  Maybe get the power bills from the power company of my tenant.  


  • hot_rod
    hot_rod Member Posts: 15,392
    I’d start with a heatload calculation, next an assessment of all the radiators.

    The load calc room by room tells you what you need, the emitters will determine what SWT is required. Zoning, piping, etc is part 3 the design.

    A number of folks here can do a complete / design. Or try it yourself
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Jamie Hall
    Jamie Hall Member Posts: 17,766
    Do not even think of deciding on a boiler for hot water heat without first doing a proper heat loss calculation on the house. There's no point at all in oversizing a hot water boiler, even one that modulates, and there's no way to determine how much heat a given building needs without a heat loss calculation -- "what was there before" is a miserable approach, as is trying to compare to neighbouring buildings. It doesn't take that long to do.

    From the description of the piping -- brief -- I wouldn't be surprised if the house to which you refer hadn't had gravity hot water heat to begin with and was converted. This is fine -- but you will want to take some care in arranging the zoning and piping to get even heat. Even more so since some of the radiation was converted to baseboards.

    Triangle Tube does make good boilers. So, however, do a number of other manufacturers (including Weil-McClain; anecdotal evidence from other owners is not a good guide). It is much more important that the boiler chosen is one which your installer is familiar with and likes to work with, and will be willing and available to maintain. The best boiler in the world is junk, unless the installation is done correctly and well.

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Daveinscranton
    Daveinscranton Member Posts: 60
    Near as I can tell, heat loss calculations are your friend.  The utility bills can be a bit of a check.  But folks oversize boilers a lot.  So if the current system is wildly inefficient, it can push you towards something way too big.  I like the elegant engineering of a mod con.  

    I would suggest extreme attention to dirt/magnetic separators.  The Triangle Tube design looks relatively insensitive to water compared to a lot of older mod con designs.  I would worry more about the cartridge circulator pumps with the old plumbing.  Spend a few bucks there for longevity and peace of mind. 

    The old Bell and Gossett 100 pumps would tolerate anything.  Except maybe over oiling.  Not so with cartridge pumps.

    Best wishes.  Sounds like fun!

  • mknmike
    mknmike Member Posts: 16
    A key decision factor for me with triangle tube is the fact that I can drive to their offices in about a half hour whereas a neighbor that recently needed a new blower for their Weil mclein needed to wait nearly a week in freezing temperatures and had to move out of their house while waiting on the part to arrive. That’s why I’m sticking with triangle tube.
  • Shane_2
    Shane_2 Member Posts: 161
    Just make sure that they have parts available from their offices.

    I've had good luck with Triangle and have one in my own home. That said, they went through one or two ownership changes and a new model or two since ten years ago
  • SuperTech
    SuperTech Member Posts: 1,715
    mknmike said:
    A key decision factor for me with triangle tube is the fact that I can drive to their offices in about a half hour whereas a neighbor that recently needed a new blower for their Weil mclein needed to wait nearly a week in freezing temperatures and had to move out of their house while waiting on the part to arrive. That’s why I’m sticking with triangle tube.
    The problem you mentioned about Weil McLain is the same problem with every mod con. These boilers are efficient but contain a lot of model/brand specific proprietary parts. These parts can be expensive  and most homes with hydronic heating have traditional cast iron boilers so HVAC companies and supply houses don't always have parts available. I've had trouble getting parts from wholesalers who sell the boilers. The nice thing about cast iron boilers is most repairs can be made with readily available universal parts that can be used on any brand.  Hopefully we will see that one day with the mod cons, but it seems like there are so many different brands with different designs right now. 
  • flat_twin
    flat_twin Member Posts: 299
    When our WM modcon was placed on the "discontinued" list, I started looking for spare parts. Besides keeping a maintenance kit on hand, I have a blower, outdoor temp sensor, gas valve body and a circulator as spares if needed. The WM parts were liquidator auction buys for considerably less than list price. It's a gamble that I'd never need them but I think I could get my money out of them down the road.
  • Jamie Hall
    Jamie Hall Member Posts: 17,766
    As @SuperTech mentioned, the problem of parts is not unique to Weil-McClain. Nor is it even unique to heating systems. As he also mentioned, there is a tradeoff between reliability and repairability on the one hand and parts on the other. I honestly doubt that we will see much improvement in that regard, however, as each manufacturer has their own ideas as to how to create the maximum efficiency and flexibility in their equipment -- which is a good thing in principle -- and this leads to parts variation between makes, and even within makes as model changes are made.

    There is enough demand in cars and trucks for aftermarket suppliers to make most parts available for older vehicles (not highly computerized newer ones) -- but that isn't there for heating, and most home appliances are regarded as throw away items.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 11,126
    For cars and trucks there are always junkyards for parts. JMHO but the boiler MFGs should keep parts available for 20 years minimum
  • mknmike
    mknmike Member Posts: 16
    So tonight I got into the house and was a bit surprised and pleased on this 35 F degree day and see the boiler temp was between 115-120 the whole time I was there and only the “main” pump that provides flow to the stand up radiators on the 2nd and third floors  was running.  The “addition/den” pump and the “dining room” pump that I suspect runs the whole first floor was also not running.  

    So I guess it’s possible for this boiler ive got to run at the same low temps once in continuous operation.  So maybe this boiler is somehow capable of modulating.  How?  I don’t know.  Time for more research I guess.

  • Zman
    Zman Member Posts: 7,117
    You have a non-condensing boiler operating at condensing temps. It won't last long under those conditions.

    I would suggest either repiping it using a condensate protection valve or replacing it with a mod/con.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mknmike
    mknmike Member Posts: 16
    edited January 18
    Zman said:
    You have a non-condensing boiler operating at condensing temps. It won't last long under those conditions. I would suggest either repiping it using a condensate protection valve or replacing it with a mod/con.
    Aw dang.  And I was starting to think that I wouldn’t get much improvement out of a mod con after seeming this boiler running at a low temp.

    I now need to research and understand why that’s bad.  I had thought the “condensing” part was the exhaust gas condensing and due to acidity requiring a stainless heat exchanger and marble chips before feeding condensate into the sewer line.  That’s what I’ve got in my home with the TT prestige solo 110.  

    Is this condensing talking about heating water condensing?  That doesn’t make sense if it’s not hot enough to vaporize.  So I guess we are talking about exhaust gas condensing.  So I guess we are talking about a condensate trap in the exhaust piping.  I will try to take a look at that next time I’m at the property.  There’s a big bell over the boiler I guess to let in basement air to constantly be sucked up the chimney.  I should check to see if the chimney is stainless lined.  I hope so bc there are two water heaters in series too.  Seems like a pretty nicely done setup really, but I don’t know.  

  • mknmike
    mknmike Member Posts: 16
    This article seems to provide some good reasoning for sizing a mod-con correctly. I think I get it now.

    Even a mod-con can cycle too quickly killing efficiency and perhaps shortening the life of the boiler.  

    I am starting to wonder WTF I saw in the property earlier tonight.  I know the one pump was running (surely calling for heat), but the boiler couldn’t have been firing or the temperature would have been going up. The dining room thermostat is the only one also connected to an AC system (the one in the basement), and the dining room pump wasn’t calling for heat (pump not running).  I am starting to wonder if they perhaps wired the system so the boiler fires only when the dining room thermometer is calling for heat.  When I turned up the dining room thermostats this past fall, that’s when I started sweating with 190 F boiler temps.  

    The upstairs thermostat is an ancient one that actually sparks inside the metal box.  It’s pretty cool, but maybe not so cool.  There’s another thermostat up in the second floor hall for the AC system that’s on the third floor.  So this second floor heating thermostat is no “brain” of the system, nor is the heating only thermostat in the addition/den.  

    Anyway, this is my first hydronic system with multiple zones.  I think I can understand when a mod-con boiler calls for heat.  Both of the following conditions must be met:
    - water temp is below the set curve (considering outside temp)
    - at least one zone/pump is calling for heat. 

    So with a “cold start” boiler like the one in this newly purchased property, with 3 pumps/zones, I’d expect it to fire if both of the following conditions are met:
    - water temp is below set point of 180 F
    - at least one pump/zone is calling for heat.  
    I think both these conditions were met tonight, but the water temp was only 115-120 F.  I wasn’t paying attention really well, but I do think I recall the temperature going up a little, from maybe 116 to 118.  I’m obviously not sure, but if this is the case, the burner must have fired, and I didn’t notice.  Wait.  I wanted to remove the cover but thought better of it because I could hear the burner. Maybe it was actually burning ALL that time I was down there.  If so, then yes, somehow this burner is not cooking up the way it did before.  I guess I need to figure out what portions of the house are on what zones.  Maybe the addition and dining room zones (which weren’t firing tonight) are tiny and the zone that was running tonight is massive.  That could be another possible explanation for the low water temps tonight.  

    I now feel the urgency to assure I’m not dripping natural gas combustion acid all over my cast iron boiler.  
  • Daveinscranton
    Daveinscranton Member Posts: 60
    40 years ago I saw a condensing cast iron boiler.  I was buying fancy flue pipe for a wood stove.  Henry looked like he smoked pot nonstop.  After talking with him for 5 minutes, I was convinced he had never seen a joint in his life.  His father was a plumber.  He inherited a plumbing and heating business.

    He had a small old cast iron boiler to heat the shop.  Which was big.  He had rigged it to burn outside air.  And built a very nice stainless heat exchanger to condense his flue gases.  It pretty much was dripping out lukewarm water.  But the boiler itself was fine.  Intrigued, I asked Henry about it.  He said that the gas company had been there twice to change out meters.  Third visit they brought cops and guns, convinced he was stealing gas.  He wasn’t.  30 minutes later, the gas folks and the cops were trying to buy one.  It wasn’t for sale.  

    Henry has been dead for decades.  I do think that you would be well served finding the equivalent of Henry, and they are on this site, for an opinion, to look over what you have and what to do.  

    Best wishes 
  • mknmike
    mknmike Member Posts: 16
    I agree that I should get someone to do a heat load calculation.  Perhaps this boiler is undersized when considering the massive basement pipes.  

    I am in WILMINGTON, DELAWARE and only about 2 miles off I-95.  I believe that Burns & McBride has been servicing this boiler which was in a dark room made of fixed louvre doors surrounding the heater and water heaters.  I had all that ripped out to clear out the basement. So now everything is much easier to access and see what’s going on with all the pipes.  

    I had a bad experience with hydronic when installing the Triangle Tube Prestige Solo 110 in my current home.  I bought the heater myself over 10 years ago, and it seemed the technology was fairly “new” then.  Again, I chose TT due to their proximity and knowing parts can be tough to obtain for these mod-con units.  A friend of mine was paying someone to install a Weil McLain mod-con and re-piping the whole house, removing the massive pipes he said were steam pipes, claiming downtown West Chester, PA provided steam from the city directly to homes.  (This Wilmington, DE house I purchased appears to also have a capped 2” inlet pipe that I guess could have been a water line, but maybe it too was steam. ???).  Anyway, I couldn’t get his guy to do the install, and struggled to find a contractor to install my TT.  I built a 2x4 wall in the basement, hung the unit, and piped the combustion/exhaust air pipes, and finally found a smaller company to do the install.  I left the manuals for the guy and wasn’t there when he did the install, but he did all the following wrong:
    - piped the water lines backwards on the primary boiler loop.  Probably not a huge deal, but I had to get the TT tech support on the phone to go over the diagram bc the company owner didn’t believe me and my explanation of the diagram.  I got him to redo the copper piping.
    - installed the new taco pump inside down, such that it was overheating.  I flipped the pump myself.
    - set the “curve” on the heater to just always go directly to ~160 F.  He clearly didn’t understand mod-con boilers.
    - left a leaky copper fitting which I ultimately just fixed myself by re-sweating the pipe.  

    I basically learned that I could have done the “skilled” part of this install better myself, while I do appreciate the labor side of it that got the old oil tank and boiler out of my house.  My old reliable plumber told me stories of how annual tune up guys would usually just come down into basements and look for signs of really bad things and smoke a cigarette instead of doing any actual work.  After getting weak responses to tough questions myself, I think I’ve been trained to do a lot of DIY and understand my systems.  And I gave up on finding anyone who really cares to understand mod-con boilers.  Perhaps the delta in fuel savings isn’t enough to pay for the skilled labor to understand them.

    if there’s anyone on this site that wants to take a look at BOTH the TT in my house for a once-a-decade system inspection, and ALSO do a load calculation consultation on the property I bought less than a 1/2 mile down the street, I will be glad to pay for the services.  I will admit to being a tough customer, not regarding payment, but I’m not accepting a situation where a contractor thinks it’s ok to not understand the work they are doing.  

    [email protected] is my email if anyone wants to contact me directly.

    in the mean time, I will see if Delmarva power will give me the power bills.  


  • Zman
    Zman Member Posts: 7,117
    Triangle Tube makes a solid boiler and if parts are readily available, it sounds like the brand for you. That being said, that firetube design has become a commodity, you can get a very similar boiler from at least a 1/2 dozen manufactures.

    You may have walked into the boiler room at the beginning of a cycle, before the boiler reached steady-state temps. It also may be possible that the system has so much mass that the boiler never gets up to temp before the t-stat satisfies.

    Old gravity systems like yours work great with mod/con boilers. Their high mass and oversized radiators work well with low temps and allow the boiler to run at peak efficiency with very few short cycles.

    Size the boiler to the heat loss of the building.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mknmike
    mknmike Member Posts: 16
    I’d typed up a response but didn’t finish it.  Thanks for the comments @zman

    Today my wife and I took a walk around the neighborhood and I heard the AC compressor running.  I messaged my tenant, who responded that the AC was accidentally on maybe from bumping the thermostat, and thinks it was on for days.  Perhaps she’s had the AC fighting the heat on the second and third floor for days.  Oh man.  Well that’s a real drawback of having separate thermostats for AC and heat as the house does.  The AC is Unico high velocity, one in the basement, another on the third floor.  The thermostats for the second and third floors are on the second floor hall.  

    Anyway, I thought I better disclose this issue.  I think those two thermostats are just two wires each, and there’s hallways and doors between the two.  So using a single thermostat might require some significant wiring efforts.  The heat thermostat is old, and the AC thermostat is less than 20 years old with the Unico install.  

    Anyway, here’s what I’d written the other day…
    Well, Delmarva Power won’t let me have access to the power bills. So I will have to bug my tenant.  This is the kind of stuff where I feel it’s best to leave sleeping dogs lying. My tenant is great and paying far more in rent than I ever would.  If it turns out the heating bills are horrible, I will possibly have an urgent scenario on my hands.  I guess I will simply check the gas meter next time I’m there and see how much has been used since the bill was in my name.  I think I can do the same for the electric.  

    The other concern for the current heater is the amount of corrosion on the cast iron boiler.  I guess I will need to see if I can get in there and figure it out.  Maybe I can find some instructions on how to open up that boiler for a look.  

    I wonder where I should be looking for condensation, in the flue on directly on the boiler cast iron.  

    I honestly don’t know what I’ve got in the chimneys.  My 1929 home in the same neighborhood has 13x13” terracotta square chimney liner. Assuming the subject 1919 house is the same, I would think I should get some stainless liner if I’m going to continue using conventional boiler / water heaters.  I was also thinking it’s not real efficient to have two water heaters in series for just one person living in this house (despite the 3.2 bathrooms).  I could maybe add a bypass pipe to one of them or just set it’s temperature really low I guess.  Heck, I guess it might be most efficient I just set them both at low temperatures, perhaps much less heat loss than a single larger water heater.  I don’t know.

    Anyway, I think a modcon makes sense in the long run, perhaps even a combi since we’ve got the space to even keep the old style water heaters.  Maybe they won’t be big wasters if they are kept at low temps.  

    I wonder if maybe adding the modcon in a different location might make sense and migrate the different zones over to the mod-con might actually be a nice migration plan.  


    And now for the separate topic… the two story detached garage.  I am running a gas line to the garage, along with a new water line and new electric lines.  We are burying the service power line that currently runs directly above the swimming pool and trenching right past the garage.  

    I’d like to put a bathroom in the garage and make it a usable suite, but it’s currently got ZERO insulation.  It does have a first floor wall radiator and chimney.  I’m trying to figure out the best way to heat this garage (to keep it above freezing and also be able to heat it like living space on the second floor if we so desire).  I could see how maybe we end up shutting off all heat to the garage to save energy.  So I am planning on making sure the water line can be drained inside the house basement.  That won’t prevent the need for antifreeze in sewer traps, and if we decide to use hydronic with the existing wall radiator, then either using anti-freeze or even just draining it.  

    It get complicated.  So I’ve thought of going with a temporary simple solution, like hooking something up to the chimney like a wood stove, but I’d really prefer to have something on a thermostat so I can set it and forget it. Even though the pool system is drained, and there’s no water in there currently, there’s paint in the garage and probably other stuff that probably doesn’t like to freeze.  We rarely have more than maybe 3-5 days where it doesn’t go above freezing, but it’s just not something I want to have to worry about.  Yet I want the best of both worlds.

    I guess nobody can recommend a setup without seeing the property, but there’s one more thing I’d like to ultimately have, a warm water loop under the driveway to melt snow.  The house is right next to the driveway though, and the driveway isn’t really sloped.  So maybe this is a ridiculous add-on.  Just another thing to consider, and probably easiest to do from inside the house as opposed to the garage.  I don’t know though.  

    There’s a lot to consider here.  I wonder if anyone would like to consult for me.