New Boiler?

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jkon

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Thanks all for your help. After my boiler guy replaced my expansion tank he said I should probably start thinking about replacing my boiler. I have a Weil McLain tankless hot water boiler and it is 25 years old. I asked him why and he said that rust starts to kill them. He also said worse case scenario would be for one of the chambers to split causing water to flow and keep flowing until water feed supply was shut off. He said that 90%of the time however I would get a warning like water on the basement floor from a leak. My boiler guy is a good guy and has treated me very fairly for the past 20 years. I definitely trust him. He said a similar system installed would be around $5000. If I wanted a system with an indirect heating of my hot water he said that would add about another $1000.

What do you all think? I definitely do not want to come home one day with a flooded basement. How long do these boilers last? Is it time? Thanks!
 

Dana

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The worst-case scenarios happen, but are pretty rare. The vast majority of leak scenarios start out as a dribble or unexplained loss of system water (going up the flue instead of on the floor), not an inundation as the first clue. Even in the latter scenario, as long as the fill-valve is turned completely off it limits the amount of spillage to the volume of the heating system, (which has substantially less volume than the Holden Reservoir. :) ) In a typical baseboard type heating system that's less than 25 gallons, often less than 15.

Auto-feed filler valves are really more of a convenience than a necessity. If the system develops a leak the sizzle bang pop from the boiler as the system pressure drops becomes evident LONG before there's any safety concern. Check the system pressure (~12psi when tepid or cool), and just turn the isolation valve that's between the auto-fill and potable water completely off. Problem solved.

There are plenty of cast iron boilers that go well beyond 50 years that are not in imminent danger of leaking, but they're also not in imminent danger of becoming reasonably efficient. If yours isn't showing signs of a melt-down, it's worth figuring out well ahead of time. When you do, size the boiler for the space heating load, which is much smaller than what you need for a tankless coil, and size the indirect for the hot water load. The smallest boilers out there still make more hot water than the typical 40-5o gallon standalone tank.

It's probably worth installing an indirect on the existing system now though, and reconfiguring the controls on the boiler to idle at lower temp. Tankless coils usually require standby temps of 160F or higher to deliver reasonable hot water performance. That raises the standby losses to ridiculous levels, typically making the boiler room the warmest spot in the house, often by more than 10F. With an indirect you can drop the low-limit temp to 140F for an oil boiler, 130F (or even cold-starting) for a gas-fired cast iron boiler.

A 3x oversized boiler that was rated 83% AFUE is typically delivering no more than 78-80% when new, and maybe 75% at age 25 if it's in good shape and has been regularly maintained. If you replace it with something that's no more than 1.7x oversized (the AFUE test presumption) it'll pretty much hit it's numbers. ASHRAE recommends ~1.4x oversizing as the best compromise between comfort, efficiency, and reasonable recovery rates from deep setback.

The average single family home in MA in a statewide survey 5-6 years ago was bout 13-14kilowatts (44-48,000 BTU/hr), but that includes a lot of completely un-insulated older stock housing. A typical tightened up 2500' older house in Worcester will come in between 35-40,000 BTU/hr @ +5F (the local 99% outside design temp.) At 1.4x oversizing that "typical" house wouldn't need more than 50-55,000 BTU/hr of boiler output to have a very responsive heating system, with plenty of horsepower to spare for Polar Vortex events. What's the D.O.E. output rating on that 20-something Weil-McLain? (I'll bet it's over 100K, might even be 150K.)

With a couple of mid to late winter fuel bills and the exact meter-reading or fill-up dates & quantities it's possible to calculate with simple arithmetic the size of the replacement boiler that's guaranteed to cover your space heating load. Most boilers with tankless coils are at least 3x oversized for the space heating load, and that ends up cutting into both comfort and efficiency.
 

jkon

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The worst-case scenarios happen, but are pretty rare. The vast majority of leak scenarios start out as a dribble or unexplained loss of system water (going up the flue instead of on the floor), not an inundation as the first clue. Even in the latter scenario, as long as the fill-valve is turned completely off it limits the amount of spillage to the volume of the heating system, (which has substantially less volume than the Holden Reservoir. :) ) In a typical baseboard type heating system that's less than 25 gallons, often less than 15.

Auto-feed filler valves are really more of a convenience than a necessity. If the system develops a leak the sizzle bang pop from the boiler as the system pressure drops becomes evident LONG before there's any safety concern. Check the system pressure (~12psi when tepid or cool), and just turn the isolation valve that's between the auto-fill and potable water completely off. Problem solved.

There are plenty of cast iron boilers that go well beyond 50 years that are not in imminent danger of leaking, but they're also not in imminent danger of becoming reasonably efficient. If yours isn't showing signs of a melt-down, it's worth figuring out well ahead of time. When you do, size the boiler for the space heating load, which is much smaller than what you need for a tankless coil, and size the indirect for the hot water load. The smallest boilers out there still make more hot water than the typical 40-5o gallon standalone tank.

It's probably worth installing an indirect on the existing system now though, and reconfiguring the controls on the boiler to idle at lower temp. Tankless coils usually require standby temps of 160F or higher to deliver reasonable hot water performance. That raises the standby losses to ridiculous levels, typically making the boiler room the warmest spot in the house, often by more than 10F. With an indirect you can drop the low-limit temp to 140F for an oil boiler, 130F (or even cold-starting) for a gas-fired cast iron boiler.

A 3x oversized boiler that was rated 83% AFUE is typically delivering no more than 78-80% when new, and maybe 75% at age 25 if it's in good shape and has been regularly maintained. If you replace it with something that's no more than 1.7x oversized (the AFUE test presumption) it'll pretty much hit it's numbers. ASHRAE recommends ~1.4x oversizing as the best compromise between comfort, efficiency, and reasonable recovery rates from deep setback.

The average single family home in MA in a statewide survey 5-6 years ago was bout 13-14kilowatts (44-48,000 BTU/hr), but that includes a lot of completely un-insulated older stock housing. A typical tightened up 2500' older house in Worcester will come in between 35-40,000 BTU/hr @ +5F (the local 99% outside design temp.) At 1.4x oversizing that "typical" house wouldn't need more than 50-55,000 BTU/hr of boiler output to have a very responsive heating system, with plenty of horsepower to spare for Polar Vortex events. What's the D.O.E. output rating on that 20-something Weil-McLain? (I'll bet it's over 100K, might even be 150K.)

With a couple of mid to late winter fuel bills and the exact meter-reading or fill-up dates & quantities it's possible to calculate with simple arithmetic the size of the replacement boiler that's guaranteed to cover your space heating load. Most boilers with tankless coils are at least 3x oversized for the space heating load, and that ends up cutting into both comfort and efficiency.
 

jkon

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My house was built in 1990. It is very well insulated. My boiler is located in unfinished basement. After 25 years I have got my $$ worth. Our present system is oil fired hot water with a tankless. Since it's just my wife and I living in our house, we are going to stay with a tankless system. My guy is going to install an entire new system, new valves, pipe, circulator, etc. He suggested a New Yorker Model: CL3-105. I did some research and although there are no reviews that I can find, it seems to be a pretty good cast iron boiler. He said he wouldn't recommend anything but a cast iron. All installed he wants $4500. He at first did mention a Peerless but he said they keep raising their prices and would cost more. Is $4500 installed a pretty good price? Thanks.
 

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The standby loss of a boiler kept a high temp so that the tankless coil is useful is the same whether it's a 1-2 person household or a 7-8 person household. The efficiency hit from being oversized for the heat load is also the same whether it's a small household or large household. An indirect is still the rigth thing to do, sizing the boiler for the heat load (to the extent possible.) You'll get more comfort and lifespan out of the boiler if it's sized correctly for the heat load rather than what's needed for domestic hot water performance.

Most houses built in 1990 no longer qualify as "very well insulated" , but they're not energy pigs like some of the uninsulated 1940s & 1950s stuff. That vintage house usually has 2x6/R19s with clear-glass U0.5-ish double-panes, R30 in the attic, and no foundation insulation (maybe some R19s stuffed i the basement ceiling) with air leakage of about 5-9 air changes per hour @ 50 pascals (sometimes more, but it would feel pretty drafty at 10+ACH/50.) A 2500' house like that would run under 30,000BTU/hr @ +5F if it's reasonably tight, unless it has an unusual amount of window area.

The New Yorker CL3-105 has a D.O.E. output of 91,ooo BTU/hr, more than 3x your likely heat load. Even if it's higher than that (for whatever reason), there's no way it's anywhere NEAR 91,000 BTU/hr, and it would be highly unusual for a 1990 vintage house to have a heat load of even 40K. But we can figure it out about where the heat load is from the fuel use numbers in under 5 minutes.

If you have a regular fill-up service, do you have a few mid or late winter fill-ups with a "K-factor" stamped on the slip? It's simple arithmetic to derive the heat load from the K-factor (= heating degree days per gallon).


I'm not convinced the W-M is toast yet, and you don't have to wait before it's rational to install an indirect. With an indirect hot water heater and a heat purging economizer control like the Intellicon you can buy back a LOT of efficiency out of that boiler by running it at lower temp, with longer but fewer burns. But if you're convince that a boiler swap is still the right course of action at this time. At $4500, installed price the contractor isn't gouging you, the only question is whether it's worth keeping the W-M for another decade. If it's steady-state efficiency tests at over 80% with a combustion analyzer after a tune up my personal inclination would be to keep it, stop using the tankless, install both an indirect tank and an economizer control. YMMV.

If you're still headed down the swap-out road, a pretty-good inexpensive oil boiler of more appropriate would be a 3-plate Biasi B-3. At about 61,000 BTU/hr D.O.E. output it's "only" 2x oversized which means it'll run a measurably better duty cycle than the CL3-105 (an you'd still have enough boiler to heat the place at -50F, just in case a new ice age is coming. :) ) Unfortunately there are very few oil boilers that run much lower output than the ~60K range. A Biasi B3 should come in $300-500 less than a New Yorker CL3-105, add $600-1000 for the indirect and it's a few hundred more, but not a grand more. Any difference in price would be made up in lower fuel cost in under 5 years (even at this year's lower oil pricing), possibly less than 3 years (at the recent 5 year average.)
 

Tom Sawyer

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IN 40 years I have never seen a Weil McLain, cast iron boiler catastrophically fail.
 

Dana

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IN 40 years I have never seen a Weil McLain, cast iron boiler catastrophically fail.

His could be a first- ya never know! ;-)

A few hydronic boilers in Worcester MA froze up and split before power to those homes was restored in the days following the ice storm of December 2008. (A good argument for insulating the foundation walls and air sealing the basement...) Can't think of any others going south that fast, but drips & leaks? Sure!

Seriously, if the thing can be tuned to 80% or better, spend $1000-1500 on an indirect & heat purge controls and save 100+ gallons per year. In the unlikely event that it fails in short years you can still use the indirect with the replacement boiler. $4500 would be an OK price if you actually NEEDED a new boiler, but it's a lot of money to spend on something "just in case".

Just how badly oversizing a boiler can be without heat purge controls, download and read this bedtime story. See Table 3, System #1, and take a peek at the "Annual Efficiency (%) Oversize = 3" column. That's an ~84% efficiency boiler that does ~75% as-used efficiency- that's your system in a best-case scenario. If your idling losses are higher than 1.2% (likely, for any boiler that vintage), you'll be doing worse than 75% AFUE, possibly MUCH worse.

System #3 is an Energy Kinetics System 2000, which comes with an indirect + heat purge controller. You can get pretty close to that with retrofit economizers, but since you'd need to keep the idling temps high to be able to get any performance out of the tankless coil it means you can't purge down to a low enough temp to make that much of a difference. That's why adding both the heat purging economizer AND an indirect makes sense.

And that's why replacing the existing boiler with another 3x oversized boiler w/tankless makes NO sense. A smaller boiler, with an indirect + heat purge control is the ticket.
 

Tom Sawyer

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The downfall of the old 66 series Weil McLain is that it is a single pass, pin exchanger boiler so it's flue temps are pretty high which is an indicator that the exchanger only does a half assed job of scrubbing the heat from the fire. It also has problems with secondary air leakage around the front plate and many just will not start and stop smoothly without introducing 2ndary air through the bottom opening that is out there for just that purpose. Still, it's a workhorse and all but indestructible. When the do leak, it is usually the section seals and not the cast itself. I like the Biase much better. It too is cast iron but it is a two pass with much better efficiencies and smoother operation without having to add secondary air. It can be further down fired also and equipped with modulation controls makes a formidable challenger to condensing equipment.
 

Dana

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The Biasi B10 series are all 3-pass, not 2, and priced attractively. (That's not to say that it's going to be worth scrapping a perfectly functional Weil McLain that has a decade of life left.)
 
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