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Controlling hydronic heat

I am considering changing the location of my thermostat to "trick" my radiator heating system into keeping the radiators at @ 70 or 80 degrees, which I think will keep the majority of my home in the low 60's. Currently, the system runs infrequently to much wider extremes, causing the house to feel chilly just before the system comes on, and 100 degree plus temperatures in the radiators at the end of the cycle. Would this be more efficient? Would this cause undo wear and tear on my high efficiency boiler/water heater? Would I do better with a different control system altogether? I have a circa 1920's, 2 1/2 story home which could use a window upgrade, but I think by keeping the radiators at a more consistent temperature, I will make the house more comfortable.

Re: Controlling hydronic heat


I don't think moving the T-stat would make much difference, since the heat of the hot water circulating thru the rads is controlled by the boiler HW control (aquastat), which sits somewhere on the front of the boiler; you can Google "images for Honeywell hi limit/lo limit aquastat" to determine the location of these controls, or perhaps call in your heating service person to check everything out.

Or you could consult the site below to determine the "Hi" settings for the high HW setting and the "LO" setting for the low HW setting---these are typically 180 degrees for HI and 160 for LO---you can adjust these down lower to for example 160 HI and 140 LO to see if the rads give you a more comfortable response.

Note: there should always be at least a 20 degree difference between HI and LO settings, so the boiler will operate properly, and the LO should not be set below 135 degrees if your domestic hot water (hot tap water) is run off your boiler water (usually is).

The aquastat, as noted, usually sits somewhere on the front of the boiler in a gray box; the cover is held on with a small stainless steel setscrew, which can be removed with a small screwdriver.

Consulting the "images" site, the first, 5th and 6th images clearly show the setting options; clicking onto the image will provide a larger image that's easier to read.

In regards to installing new, double-pane windows---this is an excellent idea; don't put off having new windows installed if they are needed, as you say in your post--they will make a considerable difference in your saving on heating bills in the winter & cooling bills in the summer, so they pay for themselves in a relatively short time; also check the insulation in your exterior walls & attic---the heat swings you are experiencing with your radiators may well be caused by the rooms of the house not being able to hold the heat the radiators are producing; if the heat is escaping thru uninsulated walls & loose windows the house will feel uncomfortable & the T-stat will repeatedly call for heat (turn on the boiler) in an attempt to keep up with the heat being lost. Do you have high heating bills?


Re: Controlling hydronic heat

The frequency with how often the boiler cycles on and off can be adjusted on the thermostat. With old analog t-stats there is a small lever on a dial behind the cover. With the new digital thermostats you'll need the manual for your thermostat. They tend to come preset for hot air systems so the settings may need to be changed to get appropriate cycling for hydronic systems. Excessively short cycles aren't good for efficiency of wear and tear but you shouldn't have to freeze and bake at each end of the cycle.

Caution: the dial behind the cover of analog t-stats contains a small heating element and exposed low voltage conductors.

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