Thermostat that lets ME control the cycle rate?

[J.Albert]

What I have: Burnham gas furnace, hot water, model P205 WI (it's 30 years old but still in good condition) There's no stack vent (it had an old HyTemp which I've disconnected electrically and locked open). No fans of any kind. Electric circulating pump. House is old (but not large) and has big cast-iron radiators.

I was having some problems (furnace wouldn't start correctly), had my plumber/heating guy come over. Checked the pilot/ignition, cleaned the sensor. He installed a new thermostat (old one must have been 40+ years old). The new thermostat is a Honeywell "round" T87K1007. There are only two wires from the furnace that connect to it. No fans, no air conditioning.

The furnace still wasn't right afterwards, but I investigated on my own and came to the conclusion that the intermittent ignition module (old Honeywell S86H) had something inside that was failing. I replaced it with a new Honeywell "universal" module (S8610U3009/U), and that seems to have solved the problems with the furnace.

But I find that the new thermostat is quirky. The "room temperature" indication (bottom pointer) seems to have no relationship to the "desired temp" setting (top pointer that you set by rotating the dial).

I checked the thermostat's DIP switches (it has these instead of the "predictor" that the old one has), and found one that wasn't set according to the manual, and reset it.

But... I've come to the conclusion that the thermostat doesn't do what I want it to do. Please keep reading.

I understand that a thermostat is intended to automatically maintain room temperature within a slight variation from the desired target setting. Perhaps within 1 degree +/-?

The result is that the furnace cycles on/off too much for what I want.

What I've been doing (it's still cold at night here in southern New England yet) is setting the thermostat up higher than where I want, letting the furnace run for an hour, then turning the thermostat down (and furnace off) until it gets a little cooler than I like.

I can repeat this two or three times a day, and that's all I need.

So.... I know there are "smart thermostats" one can buy, but I still don't know if they can do what I want. Which is:

- set a high temp limit (furnace shuts off)

- set a low temp limit (furnace turns on) Say, set my low for 64 degrees and my high for 70 degrees. Or something like that.

Are there any thermostats out that that work this way? Or do they ALL "cycle within" a smaller range of temperature change?

[Ed Pawlowski]

Yes, but you don't have a furnace, you have a boiler. The boiler will have limit switches on it that will shut it off at a maximum water temperature for safety. The thermostat controls the circulator pump.

[Dean Hoffman]

This is a bit dated but might help:

[BQ340]

Are the cycle rate switches both set to "On"? That will allow 1 cycle per hour.

MikeB

[J.Albert]

This thermostat has DIP switches.

There are 2 of them. Here are the possible choices: on/on - steam or gravity (1 CPH) off/on - high efficiency warm air, hot water, or heat pump (3 CPH) off/off - gas or oil warm air (5 CPH) on/off - electric warm air (9 CPH)

Because mine is gas/hot water, I have the second choice above selected.

Should I try the on/on position, then?

Actually, even with that, it's still not what I would prefer. I want the furnace to come on when room temperature drops to, say, 64 degrees. I want the furnace to STAY ON until the temperature reaches

70 degrees, then shut off until the temp again drops down to 64.

Are there any thermostats that can do that?

[danny burstein]

This is usually set to minimize temperature swings, but if you turn it the other way, who knows?

[mike]

Emotion aside... What is it that makes a stable temperature undesirable? Can you put back the old thermostat? The thermostat datasheet suggests that the jumpers might be setting the number of cycles...but that's vague. You can emulate the predictor by putting a resistor in series with the thermostat and placing the resistor proximate to the temperature sensing element. You'd have to do a lot of experimenting to determine the resistance and proximity.

Try bolting the thermostat to something with large thermal mass and restricting the coupling between the air and the sensing element.

They're doing what they were designed to do.

High/Low setpoint thermostats used to be all over ebay for less than $10, but all the ones I checked were "no longer available".

I'm still struggling with why it's worth a lot of trouble to make your temperature unstable.

When modifying HVAC, it's important to ask yourself two questions...

1)What might go horribly wrong? You can easily convince yourself that any catastrophic failure is highly unlikely. Problem with statistics is that they are useless in the individual case. A pregnant teenager is not comforted by arguments that birth control is 99% effective. 2)Will my fire insurance cover my stupidity?

[thekmanrocks]

I think J.Albert is trying to use this particular model in a setback manner. What he needs is a programmable thermostat or even an older mechanical setback with just one adjustable setback period.

I know if the temperature in my house swung up and down like something at Six Flags I would not be too comfy, especially in Winter.

Also, are Albert's radiators properly bled, does he have a circulator installed in his system, and.... Are the radiators free and clear - that is, nothing directly on top of, to the sides of, or in front, blocking their radiating properties? And is thermo on an interior wall, away from windows, exterior doors, and from any radiator?

[Dean Hoffman]

Well, according to the article I cited Honeywell works a bit differently than all Lux thermostats and the Hunter 44550 Auto Save.

"All Lux Products thermostats come with swing control as does the Hunter

44550 Auto Save. What is a mystery to those looking at thermostats is why there is no swing control on Honeywell thermostats. It is not a simple oversight on Honeywell?s part. Honeywell is one of the earliest makers of control technology for the home and they have deliberately done away with the idea of swing control."

[trader_4]

That's right, at least with the Honeywell thermostats that I've used recent ly. They set the number of cycles per hour desired, not a temp swing range. I'd be surprised if even an old mercury thermostat with a heat anticipator could do a 6 deg swing. Nor do I see why anyone would want it. I'd call t hat a busted thermostat.

[thekmanrocks]

trader_4:

Sounds like H-Well went cheapo post-mercury bulb jobs. Offering just a few presets in the form either of dip-switches or 3 menu choices of # of firings per hour.

With the old heat-insemenator-antessimator GOL-DANGIT - Anticipators(!), like on the mechanical HW setback formerly in my parents place, if one knew what they were doing, they'd measure the voltage to set the anticipator by, and could get the temperature swing to less than one degree F° above or below desired set point.(as long as the thing was mounted perfectly level on a wall near no drafts)

[trader_4]

IDK exactly how much my HW fluctuates by, but it's not perceptable and the display always shows whatever it's set to, once it attains that temp. I don't see how it can have anything to do with the cost of the thermostat, it's just an algorithm in software. I would think it was probably to reduce energy usage, ie by not having the system cycle excessively. But then part of it I don't understand. The number of cycles you get if you set it for a new, high efficiency furnace is less than if you set it for an old one. You'd think it would be the other way around, ie that an old furnace has more mass, takes longer to warm up, so it would be better to cycle that one less than a new system.

And as I pointed out, I don't think you could get his 6 deg swing example with one of his old type thermostats either.

[J.Albert]

I want the furnace to run only once every few hours. I'm willing to put up with the temperature swings as a result of doing so. I realize that may be different from what most others might want or expect. But that's what _I_ want.

That's what I'm doing now. I turn the thermostat "way up" before bed, let things get just a little "overly warm". Then I turn the thermostate "way down" so that the furnace won't run at all overnight. Of course, it's on the chilly side in the morning, so I repeat the process. A good "warm up" in the morning seems to last all the way into the evening at this time of year.

I'd like to set those "wide swing points" on the thermostat itself. But if I can't, I'll just set them manually (I'm retired and home most of the time).

[Dean Hoffman]

Would it work to put some sort of a timer between the thermostat and the furnace? The furnace wouldn't kick on no matter what the thermostat does for a set time.

[trader_4]

That still doesn't explain *why* you want it.

Most people do that with a programmable thermostat that automatically sets it back at a time you set at night and resumes it again at a time you set for the morning.

If you choose the resume time an hour or so before you get up, then it's warm. Also, many new Honeywell and many similar thermostats have adaptive recovery where you just set it for a desired temp of 70F at 7AM and the thermostat figures out from experience what time to fire up the heat so that it will be 70F at 7AM.

You might find some thermostat that allows a 6F range between swing points, but I tend to doubt it, for obvious reasons. And you won't find it with one that uses cycles, like the HW one that you have, because they don't have a range that can be set at all. What kind of thermostat did you have before that allowed this kind of operation? Where did it go? I've never seen one that could work the way you describe.

[Ed Pawlowski]

I mentioned that he has a boiler and it has a high limit switch that turns off the burner, but there was no response. It really makes no sense to intentionally have wide temperature swings as you have discomfort with no benefits.

My guess it is a completely misguided attempt at something.

[trader_4]

That is almost certainly what they are doing. I have a HW VisionPro and that is exactly what it does, you set the number of cycles per hour that you want the system to run. It will target that for when it's maintaining the set temp. They also have guidelines like he posted for different suggested cycles based on type of sytem, eg gas, electric, etc.

I don't see how that solves anything. A resistor is like the heat anticipator that old thermostats had. All it can do is cause the thermostat to warm up quicker than the room and turn off the system a bit early. The idea there is that there is residual heat that will then bring the room up to the final set temp. He wants a 6 point swing, which would mean you'd have to trick the furnace out in the opposite direction, ie make it go way past where it would otherwise turn off. He's need a cooler, not a resistor.

That would potentially create wider swings. But practically, IDK how much thermal coupling he'd get as opposed to it reacting to the air entering the thermostat.

+1

Those are considerations too.

[mike]

You have the right to want what you want. BUT If you disclosed the details behind what you want, some of us might decide that we wanted to do that too. At this point, it seems that nobody can see any benefit so they won't waste effort considering a solution. The thread is devolving into name calling, as internet discussions always do.

More people thinking about it positively can result in a quicker solution.

IRRC, somebody mentioned that you have a boiler, not a furnace. I missed the response to that. Seems like the answer might be relevant.

My thermostat has the ability to set different temperatures at different times. I'm home almost all the time, so I set it at 66F and don't worry about it. If I'm cold, I put on a thicker shirt.

Thermal mass should be able to do that.

[mike]

The intent was to emulate the anticipator. I'd have to agree with your statements. I was thinking that the thermal mass of the resistor would heat rapidly when the furnace was on, but cool slowly by convection in air when the furnace was off. You'd have to do a lot of experimenting...

I couldn't tell from the specs, but it sounds like the sense element is a thermistor that could easily be coupled to thermal mass.

[thekmanrocks]

trader_4 wrote: " IDK exactly how much my HW fluctuates by, but it's not perceptable and the display always shows whatever it's set to, once it attains that temp. I don't see how it can have anything to do with the cost of the thermostat, it's just an algorithm in software. I would think it was probably to reduce energy usage, ie by not having the system cycle excessively. But then part of it I don't understand. The number of cycles you get if you set it for a new, high efficiency furnace is less than if you set it for an old one. You'd think it would be the other way around, ie that an old furnace has more mass, takes longer to "

I do believe the firing 'presets' are cheaper to mfg/install inside the stat than old fashioned sliding anticipators. But I've become pretty adept at setting anticipators by feel, and by indicated temperature, so I trust them more than the new stuff.

Another elephant in the room affecting firing rates that few people - in America at any rate - consider:

The room or structure itself! How 'tight' is it? How well insulated all around. Any cracks, gaps, loose-fitting windows or doors? Uninsulated crawl spaces or an attic hatch with no stripping?

Don't even worry about replacing doors & windows unless something just doesn't operate, period.

Fix what seems to be small stuff, and you'd be suprised at the affect on the run times - of both winter heat and summer air - of your systems.