I cranked up my heating system for the first time yesterday, and I noticed that my thermostat sucks. My indoor thermometer read 66[SUP]o[/SUP], the thermostat read about 65[SUP]o[/SUP], and even though it was set to about 60[SUP]o[/SUP] the damned furnace was on! No wonder my heating bills are astronomical. If I’m going to replace the thermostat, I’d like to get one with programmable setbacks. Unfortuanely I have an old-fashioned boiler/radiator system, and last time I looked, most digital thermostats weren’t recommended for use with such sytems. Does anyone make such a thing? I know there is a long latency time for my boiler to come up to temperature, but I don’t think its more than 2 or 3 hours or so, whereas my daily schedule is in 8 - 10 hour chunks, so it should save me some money. Any thoughts?
I’m pretty sure that for a standard oil-fired (or gas) boiler, built in the past 20 or 30 years, they sell direct replacments for the “Dial” type thermostats…
One like this says it works on most systems…
But I’m not an HVAC guy, my BIL is, and he’s tasked with replacing our beat up dial thermostats this year. 
-Butler
Yeah, thats another problem. My boiler has maintenance stickers on it dating back to 1962, so its at least 43 years old, and quite likely older. It has been modernized more than a few times, and seems to have an electronic ignition system at least.
With a forced air heating system, the thermostat shuts off when the room temperature reaches the temperature you selected and the room starts cooling down. When your boiler it shuts off, but all that hot water is still radiating heat into the room. The room continues to get warmer. After a while things will reach equilibrium, and the boiler will run less often.
With a computerized thermostat you’ll be constantly raising and lowering the temperature. Lowering the temperature works ok, but raising it back up means re-establishing that equilibrium, and that takes more fuel.
That’s the way it was explained to me anyway.
You have to remember: a water-based system has two thermostats. The one in the living room (or whatever) turns the water pump on and off. That sounds like the one you’re planning to replace.
But there’s a second thermostat on the furnace that checks the temperature of the water in the boiler. If the temperature drops, the furnace goes on.
That’s why the furnace is still on when the room temperature is above the setpoint: the room is at the proper temperature, and the water isn’t circulating, but the water in the boiler needs to be heated to the proper temperature. The upside of this is that once the water is up to temperature, it can immediately circulate and warm the house without the furnace going on.
Thus the furnace goes on after the warm water starts heating the room, and stays on even though the room upstairs is up to temperature.
You may be able to adjust the thermostat on the furnace so that the water isn’t as hot, but that may affect how quickly it takes to heat the room.
The electronic thermostat upstairs will certainly help you save fuel (if you let the temperature drop at night, it will circulate less, which means the water in the boiler stays hot and requires less fuel when it does drop below the setpoint). But it would not stop the furnace from going off to bring the water in the boiler to the setpoint.
I have hot water baseboard heat. Up until a few weeks ago, I had a fifty year old boiler. I have three zones. I installed programmable digital thermostats on all three zones and they seemed to work fine. I recently had my boiler replaced & asked the plumber about the thermostats and he thought they were fine.
One of my zones is radiant heat (water pipes in a concrete floor). In that area I notice the effect that **Bewildebeest ** talks about (continues to heat up after boiler goes off), but not so much that it is a problem.
I suggest you go to a plumbing supply store (not a big box) & ask them. I love those guys.
This isn’t how I understand it. My system is a closed loop system. The boiler only heats a limited amount of water as it is being pumped through it. While the boiler will go on before the pump, it is usually a short delay. This past summer I left my system on all summer & the boiler never went on until the fall when temps went below the temps called for in my thermostats. Having said this, there are many types of hot water systems, & I barely understand mine.
Okay, I have hot water baseboard heat (which, incidentally, sucks), and there are two ways the system can be controlled: “Hot tank” and “Cold tank”.
With the hot tank system, the water in the furnace is kept at a high temperature (on my system 140 to 180F), whether or not you are heating the house (that is, no matter what setting the room thermostat is at).
With a cold tank system, the water in the furnace stays at room temperature until the house needs to be heated (that is, until the room thermostat sends a command), and then the water in the furnace is heated.
The cold tank system conserves more energy (becasue you’re not maintaining that furnaceful of water at a high temperature when you don’t actually need it), but when you crank the thermostat up, you have to wait until the water in the furnace has been heated all the way from room temperature to operating temperature before you start seeing heat in the room. On my particular system, that would be something like fifteen minutes.
My particular house is wired “hot tank”, and I simply turn off the system entirely during the summer months.
Let me clarify just a little. On a hot tank system, all the room thermostat does is open the zone valve and let water flow through the baseboards. On a cold tank system, the room thermostat opens the zone valve and tells the furnace to turn on. In either case, it’s a low voltage type thermostat that’s nothing special.
FWIW, there are two basic types of thermostats-those for hydronic and forced-air systems, and those for heat pumps. Some of the newer programmable thermostats can be used on all types of systems.
There seems to be some confusion about system operation. With a forced-air system, the heat exchanger must be cooled after the burner stops firing, and with a hydronic system, the hot water in the floor/radiators/convectors/baseboard loops will continue to produce heat after the thermostat is satisfied. To help avoid making the room hotter than desired, there is an ‘anticipator’ setting on mechanical thermostats which must be properly set to the control circuit current as marked or measured. This setting allows the thermostat to shut off a little early, and let the heat producing means have a little while to keep radiating or blowing warm air before stopping completely.
Also, you don’t necessarily have to use zone valving-some systems are set up with individual thermostat controlled circulators.