Honeywell MagicStat thermostat -> questions about jumper settings on the back

[Daniel who wants to know]

Did you read any of the PDFs?

Anyway the problem here isn't Honeywell's choice of CPH over hysteresis degrees, it is how this stat (RTH221) seems to function, when set to 5 CPH it calls for heat every 12 minutes as expected, but when set to 3 or 1 CPH in my house it only drops to calling for heat every 13 minutes, and this is after several hours to adapt. I have a 90+ condensing gas furnace and this style is only supposed to be cycled about 3 times per hour.

Also interesting with this model is that when set to 62° F as it cycled its reading would swing from 58° to 65° with each cycle while 3 other thermometers, a non-connected Lux digital thermostat, a digital meat thermometer, and an indoor/outdoor thermometer and hygrometer weather station all placed right beside the RTH221 would all show the swing as being from 61-63°. When the temp setting on the RTH221 was first set down to 62° from 68° its reading quickly dropped to 61° and stayed as the 3 others showed the normal gradual drop. When the others started to show 61° as well the RTH221 dropped to showing 60° and shortly thereafter called for heat.

It is an odd model for sure.

[Steve]

Yup... big box store junk..... There is a sucker born every minute that will buy one.

[Grumpy]

degrees, it is how this stat (RTH221) seems

expected, but when set to 3 or 1 CPH in my house

hours to adapt. I have a 90+

times per hour.

reading would swing from 58° to 65°

******************************************************************** Ok enough of this crap apparently your cheepy Tst is much more sensitive

Than the others, to make it more stable you can cover Tst with something

To see how much of effect will have, or/and if you have forced air heating

Make sure that your duct discharge is not blowing on to Tst.

********************************************************************** with each cycle while 3 other

thermometer, and an indoor/outdoor thermometer

show the swing as being from 61-63°.

reading quickly dropped to 61° and stayed

show 61° as well the RTH221 dropped to

[Daniel who wants to know]

That's what I thought at first so I wedged some plumber's putty in the corner where the thermistor is located (it sits epoxied into a small recess in the bottom left corner of the plastic housing) to add thermal mass, this showed no change. Besides have you seen how fast a meat thermometer reacts to temp changes? In air it only takes a few seconds per degree for a small change, in meat they don't call them "instant read" for nothing.

I thought about also putting a clear storage bowl or one of those anti-tamper plastic boxes over it.

Nope, the supplies are on the other side of the room.

[The Daring Dufas]

I'm afraid I didn't follow this thread that closely but did anyone mention making sure any holes in the wall behind the T-stat were sealed? That would be the first thing I always look for. I've found that even the tiniest holes can let in enough air to screw with an electronic sensor. Even air getting past/through the little plastic anchors for the mounting screws. o_O

TDD

[Daniel who wants to know]

In my case that is covered too, the thermostat is mounted to a paneling wall of the closet that the furnace is in, the walls are bare studs inside the closet, and the furnace is direct return instead of ducted with 2 20x25 filters in an A frame shape on top (it is a downflow), IE the area behind the thermostat is conditioned space.

[The Daring Dufas]

Cool! No pun intended. ^_^

TDD

[Dorothy]

replying to HVAC Guy, Dorothy wrote: Can you still purchase this thermostat

[Don Wiss]

On Sun, 27 May 2018 16:44:02 GMT, Dorothy asked:

Silly question. Of course not. That Honeywell MagicStat is 19 to 21 years old! Technology has moved on.

But if you really want old technology, you can find the ancient models for sale on eBay.

Don.

(e-mail link at home page bottom).