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Would conversion to continuous circulation / outdoor reset make sense here?

stualden Member Posts: 2
Our current boiler (oil, hot water) is about 35 years old, and last time some maintenance was performed, we noticed a leak from the boiler upon start-up which stopped (and has not started again for the last month or so) once the boiler was hot. We have an indirect water heater, so the boiler fires year-round, but rather than tempt the Fates, I thought I would start researching things for a new boiler installation (which I presume will be much more efficient than this leaky one too).

I'm intrigued by the idea of continuous circulation and an outdoor reset to control the water temperature. However, I'm sensing that this is not a solution that will be offered to me when I request quotes unless I ask about it. So I'd like to get a bit more educated so I can ask the right questions and get comparable quotes.

Originally, the setup was a four-zone conventional (baseboard heat all around) with a tankless coil. The first modification we made was to replace the coil with an indirect heater (which has proven to be vastly superior). The second modification, when we added a wing on the house, was to create two new zones for radiant floor heat. These zones each use thermostatic valves to siphon off a bit of the hot water to supply loops at a lower, radiant-suitable temperature. The thermostats for those two new zones are connected directly to circulators which move the radiant floor water around; they are not connected to the zone controller. This setup also seems to work quite well (although I have no sense of the efficiency of the arrangement).

To control all this, we currently have a Taco ZVC406 zone controller, receiving signals from the four room thermostats and the indirect heater (on priority) and controlling the four original zone valves and the boiler.

So, my question - can this setup, along with a new boiler, be adapted to use continuous circulation / outdoor reset? I am presuming that something like the Taco "FuelMizer" would be used, in conjunction with the existing zone controller. Is this worth exploring or not? Thanks for any advice!


  • Eastman
    Eastman Member Posts: 927
    Yes to your questions. Can you get off oil? That would give you many more options.
  • icesailor
    icesailor Member Posts: 7,265
    If your boiler was leaking at the bottom when it was cold, when you started it up for the season or whatever, it is toast, You may get a few years out of it, but it is leaking. The heat of the boiler will cause the water to evaporate so you don't see it. Only if the burner goes off on "safety" and the boiler gets to room temperature, will you see the water. Most pronounced on Peerless JO-JOT's and Weil-McLain 68's. It never happens to warm start boilers.
    No one did you any favors when they disconnected the boiler internal tankless coil, installed an "Indirect" with the same idea coil inside the tank (as is the now unused coil inside the boiler. They should have used a storage tank, fed off the internal coil. When they converted it to a "cold start", it allows greater expansion between the boiler sections. Because "cold start" oil boilers run dirtier, the dirt debris (Kibbles & Bits) fall between the sections and with the thermal expanding and contractions of the boiler, the debris gets wedged in harder and harder. Outward expansion is much harder than retraction. Sooner or later, the seals between the sections start to weep.

    As far as running ODR in your system, its a fine idea. Just don't run that cool Spring and Fall water through the boiler without some form of thermostatic mixing. Like a Taco "I" Series 4-way mixer that keeps the boiler at a safe temperature that protects itself, and the system temperature at the ODR temperature needed for the conditions. In other words, were you to continue to use oil, the control will keep the boiler internal water temperature at 140 degrees, the setting on the valve, but the valve allows however much hot water to enter the system, and cooler water to come back. If you use a high mass boiler (like you have now), and go to gas, you still need to maintain 120 degrees to stop corrosion in the boiler, The valve is set to this temperature.

    25 years ago and before, it was common practice to run ODR in large commercial type buildings and have colder ODR water through buildings. I know. I've had personal experience with them. ODR buildings with 3 or 4 way mixers that kept the boilers hot for other uses, never had any problems. Buildings that did not use mixers had premature boiler failures.

    Conventional Wisdom doesn't have a convention, does it?

    In 1492, Conventional Wisdom said the earth was flat, and you could fall off the edge of the ocean. Today, we still have "The Flat Earth Society. Who is correct?
  • stualden
    stualden Member Posts: 2
    Thanks for your replies, Eastman and icesailor.

    Eastman, our local utility company investigated the possibility of running natural gas in the neighborhood about 15 years ago, but I think that project died due to lack of interest at the time and I haven't heard anything about it since. So, I think I'm stuck with oil for the time being, unless you think there are other alternatives I should explore...

    Icesailor, it is a Weil-McLain 68 - how did you know, are you psychic? :) I don't think it's a true cold start system (maybe that's why you're saying "cold start" with quotes?), as I believe there is also an aquastat that makes sure the boiler fires periodically. It's the same aquastat that was there when the tankless coil was in operation, although perhaps the low temperature was turned down (I will investigate). Again, this may be a terribly inefficient arrangement--that's why I'm trying to educate myself this time to make the best possible choices.

    So, just to make sure I understand everything you said (sorry, this is new for me) - is it correct that

    1) If I'm staying with oil, I will be using a high-mass CI boiler (but a 3-pass type that will be more efficient than the old one)?

    2) A boiler like that needs the water in it to remain above ~140F all the time to prevent problems?

    3) ODR is a good idea, but mixing valves will be needed to make sure Spring/Fall water (which might be under 140F) doesn't aggravate the boiler - i.e., the boiler can maintain higher temperatures, but a "bypass" system using mixing valves will get the right temperature in the loops?

    I suppose all this may impact the performance of the two radiant loops, but in practice we turn those loops on only in the winter anyway, as those rooms are new construction and therefore much better-insulated than the rest of the house.

    Thanks again for your help - I sincerely appreciate the quick education.
  • icesailor
    icesailor Member Posts: 7,265
    I'm not getting into some of that.

    What I am saying is that if they changed the "LO" setting down to 100 degrees or lower, it is basically a "Cold Start Boiler" It really only runs if there is a call for heat. You would be better served as long as you have the '68 running to set the low to 140 degrees and the high to 160 or 170 degrees. You won't notice any difference in cost unless you become obsessive about pennies.

    When "Indirects" became the rage, where I worked, there was a guy that installed a lot of '68's. Many in homes that were not used in the winter but the heat was left on. When a call came,, and the house thermostat was set for 45 or 50 degrees, the boilers would condense like crazy. If I ever went on a No-Heat call to such a house, there was often a puddle of water under the boiler. On running boilers, there was often a rust stained area under the boiler.

    Then there were the houses before the Argo and Taco zone controllers that weren't ever wired properly and one zone would operate the boiler. The other zones would pump cold water until the connected zone called. Sometimes, these houses froze up when no one was around.
  • Eastman
    Eastman Member Posts: 927
    @‌stualden "So, I think I'm stuck with oil for the time being, unless you think there are other alternatives I should explore...

    I would first confirm that nat. gas is out, that's the cheapest fuel by far. Perhaps it's nearby and an organized group of neighbors might get the line extended down your street.

    Definitely check out propane. Others on this forum have had great success in converting from oil to propane. The general advice is to own your own tank large enough facilitating a once a year fill in the off season, when prices are the lowest. Propane opens up the possibility of modulating condensing boilers. This variable burner technology works much better with baseboard than the fixed fire on/off burners that oil continues to use.
  • icesailor
    icesailor Member Posts: 7,265
    Keep an eye on the price of Nat. Gas, oil, and Propane.

    Its always feast or famine in the controlled markets of the Vulture capitalists. They spent our money finding Fracked gas. Now, there's a glut of gas and no one to buy it, and oil/gasoline prices have been dropping like the 101st Airborne into France, the early morning of June 6, 19

    I filled up for $2.48 at Costco yesterday. Down from $3.80 over a year ago.
  • Eastman
    Eastman Member Posts: 927

    Something I forgot to mention: Find out what rate options you have for electric space heating. I can't think of the term right now, but sometimes utilities offer a substantial discount on electric that can be shut off remotely via a smart meter during periods of peak grid demand.

    To give you idea of how this would work, one poster used an electric boiler that was on a separate meter charged at a discounted rate. Since the utility could shut it off at various periods of the day, he backed the system up with propane. In his case the discounted electric was the cheapest fuel on a btu basis, but a backup was still necessary. If that's an option for you, or if you need advice comparing fuel options, just post back here and I'm sure you'll get it sorted out with forum input.
  • Gordy
    Gordy Member Posts: 9,537
    Two boilers, and controls to make it all work together seems extreme to me.