Boiler Scale Problem

Discussion in 'Boiler Forum' started by ttsmith, Jul 27, 2014.

  1. ttsmith

    ttsmith New Member

    Messages:
    7
    Location:
    Anchorage
    Hello All--

    I have a Weil-McClain gas-fired boiler heater. Last winter, it started making "kettling" type noises (bubbling and popping) and the efficiency seems to have gone down. Reading on the internet, it sounded like a scale problem. I called a plumber out, and he said that it was exactly that. I was told there is no solution. Wait for it to get worse and live with it until it is replaced, or replace it right away.

    He did use a Fernox product to treat it, however, he simply added this to the boiler and didn't flush it out. I was suspicious as to how this would help. It seemed weird that it could dissolve the scale, then simply circulate it in suspension forever. I have since learned that Fernox seems to agree with me.

    Regardless, what is the solution here? Is there a way to de-scale the boiler? Or is it really a terminal problem? It seems like Acid should do the job? I don't really want scale build up to cost me $10-15k for a boiler if I can help it.

    Thanks for any help!
    Travis
  2. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,175
    Location:
    Maine
    How old is the boiler.
  3. ttsmith

    ttsmith New Member

    Messages:
    7
    Location:
    Anchorage
    I want to say it's a 1999. That's not off by more than a couple years, I'll have to look for some paperwork to know exactly.
  4. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,175
    Location:
    Maine
    It's probably going to cost more than the boiler is worth to de scale it properly.
  5. ttsmith

    ttsmith New Member

    Messages:
    7
    Location:
    Anchorage
    What's involved in de-scaling? It seems like it should just be a matter of getting muriatic acid (or similar?) to the right parts, let it soak, then flush it out. Just as a guy at a hardware store, I can get a good bit of acid for $50-100. How long should the job take? 5-6 hours seems like a long time for what I'm picturing, but even at that it would be worth it.
  6. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,175
    Location:
    Maine
    Muriatic acid will destroy the seals.
  7. Reach4

    Reach4 Active Member

    Messages:
    2,260
    Location:
    IL
    Phosphoric acid is milder. It used to be the main ingredient in LimeAway before they went to a low/no phosphate formula. Easy to find if you know where to look. It is labeled "prep and etch" as I buy it.

    I don't know how it is on seals, but it has to be better than muriatic. It's a lot easier on hands and lungs. I am not a pro.
  8. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,175
    Location:
    Maine
    Yes process of descaling the boiler properly requires that it get removed and worked on in a safe environment than ones basement. All told the cost of doing so will exceed the cost of a new boiler and there's no guarantee that the boiler will survive the process. It's 17 years old, inefficient and needs to go anyway.
  9. Reach4

    Reach4 Active Member

    Messages:
    2,260
    Location:
    IL
    • New boiler every 17 years? Score one for hot air. Do some people use distilled water and antifreeze and thereby prevent scaling?
  10. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,175
    Location:
    Maine
    Normally scaling is not a problem. Scaling occurs when oxygen is allowed to migrate into the system and there are a number of ways that can occur. Low water return temperatures also contribute to the problem. 17 years is a long time for an appliance that runs virtually ever single day of the year for 6 to 8 months.
  11. Dana

    Dana In the trades

    Messages:
    2,841
    Location:
    01609
    Mind you, 17 years in Anchorage's 12 month heating season is the operational equivalent of 20-25 years of use in more temperate climes, which is within reasonable lifecycle norms for a cast iron boiler.

    In most of the lower 48 it wouldn't cost $10-15K to replace a cast iron boiler- something like half that is probbly the average. I don't know the going rate in AK- lots of things are quite a bit more expensive in the 49th state than they are below the 49th parallel.
  12. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,175
    Location:
    Maine
    Folks are always surprised when you mention replacing heir boiler. They have no problem with shelling out 25 grand or more every few years on a car that depreciates the minute you drive it off the lot but boy do they piss and moan over buying a new boiler. Personally, I change mine about every other year but then I have access to some pretty cools stuff at some pretty low prices.
  13. Dana

    Dana In the trades

    Messages:
    2,841
    Location:
    01609
    I know folks who swap out cars about that fast too...

    But a new boiler doesn't offer much ego-stroking & comfort as a new car, eh? (At least not for most people.) Most just want the thing to just keep on running with minimum maintenance cost (which is sort of how I treat cars AND boilers, but I pay attention to the maintenance issues of both.)
  14. ttsmith

    ttsmith New Member

    Messages:
    7
    Location:
    Anchorage
    Sorry, I didn't mean to let this die. I had been getting email updates, and then they stopped. I haven't lost interest. :)

    It's sounding like the consensus opinion is that de-scaling is not really cost-effective. I still have some trouble swallowing that, but I'm willing to believe experts on that.

    As far as where I'm coming from is this. I've been in this house ~ 2 years. When we were home shopping, I poked around some opinions on boiler life and the answer from a couple people seemed to be they should be good for 30-40 years. Just a big iron vessel that burns gas, heats water, and has little to go wrong. That's why I was fairly shocked to hear that (what I thought was a middle-age boiler) was actually dead and is going to cost me $10,000-ish bucks to replace in-kind.

    As far as the vehicle comparison goes, my daily driver is a 1994. If it breaks on the way home today, I'd repair whatever is wrong. Wouldn't dream of replacing a vehicle that new.
  15. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,175
    Location:
    Maine
    Hell, I service boilers that are close to a hundred years old but they are not efficient.
  16. Dana

    Dana In the trades

    Messages:
    2,841
    Location:
    01609
    Yep- if it's old enough to have scaling & kettling issues, the amount of fire-side corrosion and water side erosion of the fine bumps & channel detailing in the plate castings that give it good heat transfer from the higher turbulence and surface are are now past prime. The fire-side of the heat exchanger typically have an array of nipples that get thinner & shorter with use:


    [​IMG]

    These can also soot up if the boiler's fuel/air mixture goes off, or erode away if the boiler is running cold too much of the time:

    [​IMG]

    The water side has has channels & other features to enhance turbulence, which can also erode or scale up, reducing the heat transfer effectiveness.

    Either/both will reduce the maximum achievable combustion efficiency of the boiler.

    As long as it's not leaking it can be brushed out & descaled the boiler can be band-aided forever, but the steady-state thermal efficiency of what was an 80-85% efficiency cast iron boiler is headed south of 75% over time, settling somewhere in the low 70s (but only if you keep both sides of the plates clear of scale & rust.) A lot of older boilers started out at 75% steady state efficiency , and after 50 years of steady (ab)use are operating in the 50-55% range, even lower if not maintained.

    As a general rule, the cost of maintaining an older eroding/corroding boiler over 15-20 years plus the additional operating cost of the lower efficiency makes it less cost effective than replacement once it gets to that point. If your plan is to just move in a year or three and just need something to heat the place risking the up-front cash for descaling it may be worth it (it's still a gamble), but probably not if you intend to live there for awhile.

    Since the vast majority of cast iron boilers are signficantly oversized for their loads (even in the interior portions of Alaska), it's always worth analyzing the heat load before buying a replacement. Measuring fuel-use against heating degree days takes maybe half hour of looking up the weather data for a mid-winter billing period during which the place was occupied, which can be converted to BTU/degree-hour using the nameplate efficiency of the boiler, then applying that constant to the difference between 65F and the 99% outside design temp (which is about -10F in Anchorage, for a delta-T of 75F ) in under 5 minutes. This method puts a pretty firm stake in the ground- going more than 1.5 x beyond that with a cast iron boiler means will not run as efficiently as the nameplate AFUE implies, and will cycle more often, and need more maintenance. (A boiler 2x that size would heat the house even at -85F, which is well below your lowest recorded historical low temp of -38F back in 1947, yet 2x-3x oversizing is very common.)

    Measuring the radiation on each zone would be necessary for adjusting the system design, but does not define the size of the boiler (contrary to what some old-schoolers might tell you.)
Similar Threads: Boiler Scale
Forum Title Date
Boiler Forum Hydronic System Design & Boiler Piping/Control Wednesday at 6:23 PM
Boiler Forum Help Replacing an Old Boiler Sep 14, 2014
Boiler Forum Replacing old NG boiler / water heater - check my sizing please? Sep 6, 2014
Boiler Forum Combi-Boiler NCB 240 (Navien) Sep 5, 2014
Boiler Forum Nat. Gas Boiler Selection Aug 24, 2014

Share This Page