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Programmable thermostat with old cast iron radiators

corey_s Member Posts: 17
edited December 2017 in Thermostats and Controls
This is my first winter in a home with a hot water boiler and I'm trying to get it to operate as efficiently as possible. I've been looking around this site and noticed that people mention setting a minimum temp on their boiler. Is this only with combination boilers that are also used for potable water? I have a separate water heater and my boiler always cools to room temp after turning off. Also, I was given a Honeywell TH4110D1007 PRO 4000 that I installed a couple days ago. I'm upgrading from a digital non-programmable thermostat. My home was built in 1925, is about 1800 sq ft finished, and I have 9 large cast iron radiators with an older 80's Burnham hot water boiler. With the old thermostat I set the temp differential from .5 to 2. I didn't really mind the temperature swing and thought this would be the most efficient. The new Honeywell thermostat uses CHP. Honeywell recommends 3, but I've set it to 1, thinking this would be more efficient, cause less wear on the boiler, and I don't mind the temp varying a little in the house. Am I correct that this is more efficient? Would turning off adaptive intelligent recovery help with efficiency also, or just cause the boiler to overshoot?

I'm happy to provide additional details needed. Thank you for any input.


  • Jamie Hall
    Jamie Hall Member Posts: 22,147
    When you come right down to it, there really isn't much -- other than avoiding large setbacks (with your cast iron radiators, I'd keep it to 3 degrees or less) -- that a thermostat can do to boost efficiency. It's really as much a matter of how comfortable you are. I'd certainly leave the adaptive intelligent recovery on. It won't hurt a bit. Cycles per hour? Hmm... I'd try both 3 and 1, and see which felt better.

    As far as overall reduction in fuel use, you mention draughty. That's your first target. Storm windows (there are many variations, both outside mount and inside). Sealing up any air leaks you can find. Is the attic insulated? If not, why not? Makes a big difference. All that sort of thing is usually relatively low cost, and pays big dividends.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • If you have drafty and can't upgrade the insulation and such right away, setbacks will save energy. Programmable thermostats are most effective in poor insulation situations where there's a big penalty from high delta T.

    I'd say set back to whatever you are comfortable with at night, and if you are out during the day, go down to at least 62-63. It's the most you can do with a thernostat.

    The boiler's efficiency is dependent on its firing rate (heat transfer, Q), flame temperature, physical dimesions, and water temperature. All 3 of those stay more or less constant, so does the boiler efficiency no matter the cycle rate.