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Honeywell thermostat, steam heat

Steamhead Member Posts: 16,736
will hold their settings if the power to the 'stat is temporarily lost. I believe the T8600D will do that, never had a problem with this unit on steam.

If you run into a situation where the stat loses settings when the pressuretrol cuts out, wiring the stat to a standard circulator relay placed in the 120-volt feed to the boiler will solve the problem.

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  • michael_15
    michael_15 Member Posts: 231
    honeywell thermostats

    I noticed that some of the Honeywell programmable thermostats (CT3x00, perhaps others) have on the label "Not recommended for steam heating applications"). (I happen to have steam heat.) Why is that? What makes a thermostat "good" for steam heat?

    The only thing I can think of is if the thermostat uses pulsed calls for heat (like the Wirsbo WT1), which limits the duration of the heat calls if the temperature is within a few degrees of the thermostat setting. This is to avoid potential overheating, I assume. However, I thought this sort of feature was somewhat rare, and the CT3x00 isn't even Honeywell's top-of-the-line.

    What other reasons would there be for a thermostat to care that I have steam heat? Are other thermostats also potentially incompatible for the same reasons though they lack the warning on the package?

  • Steamhead
    Steamhead Member Posts: 16,736
    They probably

    don't have an adjustment for number of cycles per hour. A steam system that needs work doesn't heat up quickly, which may mean the thermostat will cycle off before the radiators get hot.

    I like the Honeywell T8600D digital programmable thermostat. It has the cycles-per-hour adjustment which I can set as low as 1 CPH if needed, a back-lit display, and doesn't need batteries.

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  • Glenn Harrison_2
    Glenn Harrison_2 Member Posts: 845
    I was looking through some of the Honeywell manuals...

    and noticed you can use the CT3600 series thermostat.

    I believe the issue with many of their thermostats is that they are power stealing thermostats, meaning the thermostat is powered by the two wires going from the boiler to the t-stat when the t-stat is not calling for heat. This can cause problems with the system operating correctly in the on cycle.

    I'm pretty sure what Honeywell wants, and what I always like to see is either a fully battery operated thermostat, or a model like Steamhead listed that requires a separate common wire from the boiler transformer to the thermostat.

    Unfortunately, most of the CT series hardware thermostats are power stealing models and this can cause problems with steam and many other heating systems.
  • Glenn Harrison_2
    Glenn Harrison_2 Member Posts: 845
    Well SH, you and I can handle installing...

    an extra relay to correct problems, but the average homeowner buying a CT hardware store series thermostat won't be able to, which I'm sure is Honeywells standpoint.

    I'm not so worried about loosing the program, which certainly can happen, as I am about erratic operation in general with power stealing stats, especially if there are any electronics in the same circuit as the thermostat. I haven't seen this happen on a steam boiler, but I have seen it happen on a boiler with electronics on it, and plenty of burned air units. So my self and the company only use battery operated thermostats to eliminate problems.

    I stand corrected on my other post, the T8600D is a power stealing model, which is why it needs no batteries. The T8602D is the battery operated model. Just to set the record straight.
  • David Efflandt_2
    David Efflandt_2 Member Posts: 24
    CT3600 works for me

    My 1-pipe steam works great with CT3600 (7 day). Similar CT3500 (5-1-1 day) worked as well in previous years. The only reason I upgraded the CT3500 was because the CT3600 keeps track of actual run time (current day, previous day, and since reset) to help determine effectiveness of setback. I didn't even need to rewire (either used same baseplate/batteries).

    I will use the previous CT3500 at work to replace a thermostat that got physically damaged.
  • BillW@honeywell
    BillW@honeywell Member Posts: 1,099
    CT series stats & steam

    The retail model stats are power stealing. Some steam systems shut down completely during the off cycle, and the display will blank out. Battery powered stats are the best bet for steam, since they don't depend on the system for power. The retail stats may not all be capable of being set to 1 cycle per hour, the usual setting for steam. Read the box carefully.
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