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Advice On Whether To Keep or Replace Existing Hydronic System's Boiler

PGB1 Member Posts: 49
Hello All!
I an new to this group and am writing to ask for some input to assist me in deciding whether or not to replace my existing boiler. Each spring I think about this, but haven't done anything yet. I'd hate to be without heat due to a winter failure, but I'd not like to discard a boiler if it is expected to last longer. My wife and do not know how long we will remain at this house. Our guess is it will be about 5 or 10 years until we're too old to maintain it and have to go.

My background experience is that I'm a master electrician by trade (Industrial & commercial is my only experience- I never could learn residential. Those guys work magic! ).
I got lucky- the company I worked at assigned me to work in tandem with some of the heating, cooling, pipe fitting & plumbing tradespeople for many years. I learned quite a bit about hydronics and refrigeration during that time. We were fortunate that we could actually work together and we each learned from, and sometimes apprenticed to, the other. I learned enough to get a mechanical contractor's license and a plumbing journeyman's card. But, I have not practiced in those fields for over 10 years, so my knowledge is fading fast. (As is everything else at my age...)

I apologize that the post is going to be long, but I thought it wise to provide as many system & equipment details as possible.

What I Have At My House-
I have a hydronic system with one pump on the return and 3 zone valves on the supply manifold. The house has a mix of fin tube baseboard radiation units and cast iron radiators. Each zone valve is a Honeywell motorized valve with end switches. The control is by a zone valve controller I built many years ago. Basically, the end switch closes and this allows the burner and pump to operate- assuming safeties are satisfied.

The boiler is a Bryant Model 26 cast iron sectional boiler from the early to mid 1950's (per Bryant). It is natural gas fired.
Years ago, when I called Bryant, the technician told me that boiler operates at 80% to 82% efficiency when new. (Amazing, if true)

It has a Thermiser on the 6" vent. It vents into a masonry chimney with a clay tile liner. (And shares with a water heater.)
The Radiation piping is a mix of original galvanized and type L copper tubing. There is some HePEX where I've added or moved radiation over the hears.

The house is from the late 1890's, but the basement was added in 1952. There are two additions- one from the 20's & one from the 40's. Based on clues from the monoflow tees and a few other parts, I believe this heating system was built in the 1950's.

Modifications I Did When I Bought The House About 35 Years Ago-
The boiler's gas system didn't have any pilot safety. If the pilot went out, gas was allowed to flow on a call for heat.
I installed a baso valve with an 24 volt gas valve after it. I also installed a new pilot burner & thermocouple as part of the project. I also made & installed a few baffle plates that lay on top of the heat exchanger between sections. Some were missing.

Additionally, I installed a flame roll-out safety in the boiler's jacket, just outside the burner area and a high water temperature cutoff. There is a carbon monoxide detector above the unit as well. There is a separate temperature control which starts the pump when the water reaches 110-F. (I probably didn't need to install this.)

I also put in a bladder type expansion tank to replace the original horizontal tank, as well as a low water cut-off device.
The system uses a Spirovent (installed about 12 years ago) for air removal, along with individual coin vents and Maid-O-Mist style vents on the upright radiators.

Basically, everything about the boiler- except the actual heat exchanger, the boiler's jacket & its burner are no longer original equipment.
The only problems I've encountered since I made stuff safe is once I replaced the thermocouple and one zone valve motor.

Every year I take the top off of the boiler and clean the sections with the long wire brushes. The furnace cement around the perimeter is inspected, but never cracked. I also vacuum everything in sight & check the flame for proper combustion. I can't think of anything else to maintain.
I keep the system water treated with sodium molybdate at 150 ppm. (GE Corroshield)

My Puzzlement-
Since the boiler is cast iron and the controls are all newer, would it be wise to replace this boiler during the off-season, or do these boilers actually last a very long time?
I've read that cast iron boilers have a life expectancy of 10 years, 20 years, 30 years and forever. So my research do date is quite inconclusive.

If I Keep The Boiler-
Would it harm the system to change to an electronic spark ignition, or does the pilot have to stay burning all summer to protect the cast iron?
Assuming I convert to spark, would it be OK to remove the Thermiser and put in a vent damper, tied to the controls so the boiler can't fire unless the damper is proven open? (I tried to find a link to explain what a Thermniser is , but came up empty. A Thermiser is basically a box with a flap in it. The flap has a hole that is smaller than the vent diameter. The idea is that it keeps the heat in the vent longer, thus saving energy. If there is an explosion, the flap will open- allegedly open...)

If I Replace The Boiler-
Ideally I'd like to use a more efficient & probably lighter weight (wall hung?) boiler, or any efficient unit, which invokes a direct vent type.

Longevity concerns me: I remember many years ago installing various brand fin tube boilers and some Hydropulse boilers at work. These were used for indirect domestic water heating. Those would usually fail in 5 or 6 years, but I'd assume the products have improved. You all know more than I ever will about longevity.

Part Two is that venting a direct vent boiler will be a challenge.
On the boiler side of the basement, the rooms above cantilever 2 feet past the foundation. If I exit there, the exhaust would run under the overhang and terminate on a patio and right behind the condensing unit for the air conditioning and at the intersection of another wall. Air intake will also be a problem because the dryer vent is within 10 feet of that wall. (There's no where to move that & stay within the manufacturer's maximum length mandates.)
The basement wall on the other side of the heating plant adjoins a 12 foot wide crawl space, so I don't think I can run a vent that long, through the crawl space & out.
And, of course, there is no floor drain nearby for condensate, although I think could use a condensate pump if they are allowed.

Assuming they fit, I am wondering if a high efficiency boiler can vent into the existing masonry chimney if I put 2 liners in? One will be for the water heater & one for the boiler. The liner is 12 x 9 tile. If that's not an option, I'd go with a natural draft unit.

Thank You-
Thank You all for your advice on whether or not to replace a functioning boiler.
Your advice & guidance is certainly appreciated.

Enjoy This Day!


    HVACNUT Member Posts: 5,025
    You had me at "1950's Bryant".
    IMO, replace everything.
    Get estimates with heat loss calculations and get options and recommendations from the contractor to suit the best application for your home.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,573
    If you select high efficiency mod con with a plastic vent system, it could probably go into the existing chimney, as the only appliance venting into it. That then would require the hot water to come from an indirect piped into the new boiler. Cast iron boilers would not have this limitation.
    Use the free SlantFin heatloss app to determine the proper size of the replacement boiler, and using advice and books from here, you can be ready to make a replacement when the time comes because you will have already made the necessary decisions.
    Assuming that the system maintains pressure, when the auto fill is closed, and that there are no small leaks, then there has not been any corrosive oxygen in the system to rot out the sections.
    Boilers of that time were made of thicker metal, with a longer life, and yours, with your diligent maintainence, may have quite a few years left in it.
    With your baseboard radiators, you may not have the ability to use lower water temperatures to benefit from outdoor reset. Comparing the rooms heatloss with the EDR of the radiator will tell you how low the temperature can go.—NBC
  • PGB1
    PGB1 Member Posts: 49
    Thank You both for your advice & ideas! They are appreciated.

    Studying a few installation manuals for direct vent types shows that some have much longer equivalent-feet of vent length than I remember from installations years ago. I might be able to pass the vent through the crawl space & out the opposite wall. That wall has no encumbrances & the crawl is a closed, conditioned space at temp of the rooms above, so no freeze worries are present. Does this sound reasonable, or am I dreaming?

    If we end up having to postpone the replacement, are vent dampers a good addition to cast iron boilers?

    Also, will converting to spark ignition cause any corrosion damage to the boiler in the non-heating season? I was told by old timer heating guys long ago that the pilot has to stay on or corrosion starts due to condensation, but the water is at ambient temperature, so that sounds odd to me.

    Thanks Again to both of you for sharing your knowledge!
    Enjoy This Day!
  • RomanP
    RomanP Member Posts: 102
    Yep. Imo if it’s not broken, don’t fix it. It’s an investment and if you don’t plan to live in the house long enough to start ripping the rewards of high efficiency system, I’d rather stay out of this. Plus, I’m not a real estate expert and don’t know if such an upgrade adds value to your house ( definitely a catchy feature for listings). Now if you decided to consider high efficiency, start out with your heat loss analysis, determine your total heat load and load for each corresponding room, to see if your current radiation emitters can operate on 150 degree supply temp. That’s when you get your promised 95% efficiency, if you have to operate system on 180 degrees, you’ll get about 89% efficiency. If you don’t leave in McMansion, I would assume a good combi unit would do the job( my current preference is Lochinvar Noble, priced very competitively against Navien and I think I’m done selling Naviens). This unit would heat up the house and provide enough hot water to run couple showers simultaneously. Venting can be done through existing chimney and intake from the side. Or both from the side... there are options. Some modern combi units can be vented with 2” CPVC!!! Up to 60’ developed length. Don’t take my word for it, read the manual pls. Please make sure you are using schedule 80 CPVC for exhaust and not regular schedule 40 PVC as some states still allow.
  • hot_rod
    hot_rod Member Posts: 19,275
    Consider how much you would want to invest. Shop around and see what all the components would cost, boiler, venting, pump, valves, misc. Is it worth 5- 8 grand? Good, solid advice above.
    Be careful with a side wall vent option, they can make a mess of the side of the house.

    If you do take on the project:
    room by room heat load
    look for inexpensive upgrades to lower loads
    determine supply temperature to determine if a mod con makes sense
    Is the zoning currently adequate
    Build a material list
    Any permits or inspections required?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SuperJ
    SuperJ Member Posts: 605
    If you do upgrade, here is are some ideas:

    Consider pulling combustion air from inside if it's an older (leaky) house with an open mech room in the basement. Then, all your equivalent vent length can be on the exhaust and give you a little more flexibility.

    If your temperatures allow, you might be able to go with a high mass drop in replacement modcon to keep the upgrade simple and allow for future system upgrades in the zones. This avoids the complexity of a primary secondary repipe.
    Think Viessman CU3A, or HTP Pioneer. Both of these boilers have no minimum flow requirement due to the amount of water they hold (Pioneer is a actual tank, and Viessman is 12+ gallons in the big HX). You could drop one into your existing system without modifying piping, (along with modern dirt/air/mag separators), and an ECM Delta P pump and maybe some new zone valves if the existing ones are worn.

    HTP Pioneer:

    Viessman CU3A Vitocrossal:

    One more thing. Don't be put off by a "mere" 5:1 turndown. Turndown doesn't matter nearly as much when you have significant thermal mass with all that water.
  • PGB1
    PGB1 Member Posts: 49
    Thank You All for helping me decide about this project.

    I really appreciate your advice and product suggestions- As well as each of your common sense approach about approaching benefits & detractions of replacement or retaining the boiler.

    Thanks for the links SuperJ. Pioneer is an interesting concept.

    That's a good point about efficiency ratings are at lower temperatures, RomanP. We do have to run at 180-F most of the winter to maintain set-point. Lochinvar Noble looks interesting.

    By unfortunate coincidence, our domestic water heater's tank started leaking this week & I had to swap it out. (17 years of faithful service). This month's budget didn't allow for an indirect to our existing boiler. We went natural draft tank style. So I just lost out on boiler heating domestic water to save the cost of a water heater. ( Unless we use the new boiler to heat incoming cold & dedicate the tank style heater as a holding tank & re-heat. Science project ahead!)

    I believe it is time for some more research & pricing on my part so we can make a more informed decision.

    Thanks Again Everyone & Enjoy This Day!
  • DanInNaperville
    DanInNaperville Member Posts: 40
    edited May 2018
    I'm facing a similar decision having recently bought a home with a (now) 31 year old Burnham Series 2 boiler.
    But as fascinating as I find the technology of condensing boilers, if I replace the old Burnham, I'll just get another one. (another "old style" atmospheric boiler)

    Some things to consider are that high efficiency boilers cost more to buy and install, and their manufacturers predict they'll last about half as long (going by most warranties and anecdotal experience). But they're more efficient when running correctly, so they save money on fuel cost.
    The working numbers I've been going with (and I'd sure like to hear reasons for adjusting them) are that an atmospheric boiler costs X every 30 years while a condensing boiler costs 1.5 X every 15 years. Condensing boilers don't condense very well when running hard (on the coldest days) which are rare but which may burn as much fuel is burned on a number of less cold days. Still, a condensing boiler will likely save 10 to 15% in fuel costs (while increasing your electric bill due to the need to run a blower moter and more resistance to overcome through the restrictive heat exchanger).
    So, over time, "fixed" costs (buy and install the boiler) are about 3 times higher for a condensing boiler but variable costs (fuel) are about 12.5% less.

    Locally, we're served by natural gas for heat, which shows no signs of getting expensive. Our heating bill last winter was around $1,000 (6K Sq Ft, including basement and garage, all kept heated). A condensing boiler would likely have cut that by $125.

    An atmospheric boiler replacement would likely be about $5,000 (well researched WAG) so my annual cost is $166 on top of the $1,000 in fuel costs.

    Buying and installing 2 condensing boilers would total to about $15,000 so annual cost would be about $500 in fixed costs plus $875 ($1,000 minus the fuel savings of 12.5%) totaling $1,375. The higher electric bill from running the blower and more water pumping costs would take that a little higher, but it shouldn't be a big difference.

    Bottom line, with gas heat, it's about $200 a year cheaper to skip the high efficiency boiler and stay with an atmospheric one. There's also less to go wrong, and fewer days dealing with no heat after some sensor or motor or control failed.

    Assuming oil costs 5 times as much as gas for heat (from comments on this board, if that's not correct, please let me know and adjust these conclusions), if I had oil heat and a $5,000 annual fuel bill, it would be cheaper to go with a condensing boiler, since fuel savings would be 5 times as much, and net savings would be $250 per year to go with oil burning condensing boilers vs. atmospheric.
  • PGB1
    PGB1 Member Posts: 49
    That's a very impressive cost analysis you did Dan. Doing similar calculations, I came up with too long of a payback period to use a condensing boiler.

    We don't know how long we'll stay in our house and, in our house, added home resale value due to a high efficiency boiler isn't a factor. The wrecking ball doesn't care. (Older houses like mine are splatted & giant McCheaps are built in their stead.)

    Thanks for sharing your calculation!
  • RomanP
    RomanP Member Posts: 102
    The bigger the property, the faster you’ll get your returns
  • RayH
    RayH Member Posts: 89
    Install a Baxi wall hung and vent directly outside.
  • DanInNaperville
    DanInNaperville Member Posts: 40
    PGB1 said:

    It vents into a masonry chimney with a clay tile liner.

    There's a good chance you're getting better efficiency than typical. If you get one of those laser pointer remote thermometers from Harbor Freight, you can check the temperature of the wall or exposed brick that's adjacent to the flue. There is likely some condensing going on in that flue, and some part of the re-captured heat is being radiated back into the house. The beauty of a system like this is that it recaptures heat when the boiler is working hard (and burning a lot of fuel), not just when it has modulated way down.
  • Jamie Hall
    Jamie Hall Member Posts: 21,106

    PGB1 said:

    It vents into a masonry chimney with a clay tile liner.

    There's a good chance you're getting better efficiency than typical. If you get one of those laser pointer remote thermometers from Harbor Freight, you can check the temperature of the wall or exposed brick that's adjacent to the flue. There is likely some condensing going on in that flue, and some part of the re-captured heat is being radiated back into the house. The beauty of a system like this is that it recaptures heat when the boiler is working hard (and burning a lot of fuel), not just when it has modulated way down.
    An excellent point which is very often overlooked! Bottom line there is that if the chimney and the boiler are within the heated envelope, the only losses are from incomplete combustion -- which a competent burner technician can pretty well eliminate -- and the remaining heat content of the stack gas where it exits the building -- not where it exits the boiler.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • PGB1
    PGB1 Member Posts: 49
    Dan & Jamie, I apologize for my very delayed reply to your posts.

    Thank You Dan for the interesting thoughts about chimney radiated heat. Once, for fun, I tried that on the masonry portion above the roof while up there clearing snow. (If I remember correctly, the delta temperature was minimal.) I never thought to check inside. It will be fun to find out how much heat I'm retaining.

    Thanks Jamie for your comment about incomplete combustion. I never thought about that part of the equation- although it is a very real part!
  • John Mills_5
    John Mills_5 Member Posts: 946
    There are 2 different efficiency numbers here. The claim of 80% efficient means combustion efficiency. When fully warm and tuned properly, it may test with a combustion analyzer at 80%. But boilers don't run 24 hours a day in a house. So there's annual efficiency or AFUE. That's the number thrown around by salesmen and looks at everything like standby loss, inefficiency during warmup and heat lost during cool down. An old beast like the Bryant could have a combustion efficiency of 80% but an annual efficiency of about 55-60%. It takes a while to warm up with heat pouring up the chimney then when it cools down, heat is still pouring up the chimney without a flue damper.

    If you are running 180° water, I've seen figures saying more like 85% AFUE out of a mod-con. That's about what the best simple cast iron boilers are rated at. Did I miss your radiation? If copper fintube baseboard, the national trainer of a major brand said in a mod-con class he'd go with cast iron for that personally.
  • PGB1
    PGB1 Member Posts: 49
    Thanks John (and I apologize for my late reply).
    I appreciate the interesting information.

    Due to unexpected emergency expenses- we have to keep the boiler for at least another season.

    Our radiation is a mix of copper fin tube and we have 3 upright and one horizontal radiators. We also have one fan-coil toe space heater.
    So, other than radiant tubing, we've got quite a smorgasbord!

    I wonder if it would be wise to add a vent damper (removing the Thermizer). I'd tie it in with an end switch for safety, like factory ones are wired.

    I also wonder if converting to spark ignition is a good idea or a waste. We do keep the pilot on all year because it gets cool here at night in summer. So spark would save that energy, but could that cause problems with the old heat exchanger?

    Thanks Again!