The kid meets the furnace thermostat...

SoundGuy wrote:

dougrainer wrote:
I Know about battery powered. But, not really needed for a basic mechanical wall furnace tstat. As another posted, what happens when the battery goes dead? Doug

Seriously? Install a fresh set of AA batteries in the thermo at the beginning of each season - problem solved. :B

Yep, changing the AAA batteries in our two Honeywell programmable thermostats is on our New Years Day "ToDo" list. Haven't had one fail us yet...

2oldman wrote:
You don't have air?

I was wondering the same thing. Is the 2-wire setup just for rigs with a furnace only and no air conditioner?

What about a 2-speed fan? Doesn't that require an extra wire?

Ron3rd wrote:

2oldman wrote:
You don't have air?

I was wondering the same thing. Is the 2-wire setup just for rigs with a furnace only and no air conditioner?

What about a 2-speed fan? Doesn't that require an extra wire?

He may have a ceiling unit with an integrated thermostat. They're fairly common in smaller Class C's and TT's.

The two wire thermostat is for furnace only. When the thermostat calls for heat it just connects the two wires together. When the temperature is reached the thermostat breaks the connection between the two wires.

The AC is on the ceiling and controlled by turning the knobs on the unit itself to both turn it on as well as adjusting the temperature.

There is no additional wiring needed to replace a 2 wire mechanical thermostat with a battery powered digital thermostat.

There is only one fan speed for the furnace. The high/low fan speed is for air conditioners not furnaces.

1. Pull the cover off the mechanical unit
2. Remove the two screws holding the unit to the wall
3. Disconnect the two wires off the back of the old mechanical unit
4. Carefully drill new mounting holes for the new thermostat.Connect wires according to instructions, 1 wire to the positive terminal and the second wire to the heat terminal
5. Install batteries and test
6. If no operation swap the wires
7. Mount thermostat on the wall.

This swap is relatively easy and should take about ten minutes.

Hi im back, the OP.
I am waivering on digital vs mechanical.
A couple mechanical thermostat questions..

-I have discovered the heat anticipator. Referenced in a 2 wire system. I read that one common type is like a nicrome wire resistor that heats the thermostat. How is this possible in a 2 wire no electricity system?

-Snap action thermostat? LuxPro has one (with anticipator) Are these good?

-the old bi metal spring. If i remember correctly, my thermostat might have a very week magnet in there somewhere. Is that an anticipator?

The heat anticipator controls the length of time the furnace operates per cycle. It should be adjusted to the furnace control (milli)ampere setting listed on the furnace or measured thru the stat wires.

I am confused by the phrase "2 wire no electricity system". What is the purpose of the wires, if not to conduct electricity?

Snap action and bi-metal depend on flexing of metal due to temp changes, to open and close the stat contacts.

The magnet inhibits contact chatter.

The advantages of many digital stats are not insignificant.
Easy to read lighted digital display
Adjustable cycle rate
Adjustable min/max temp settings
Low stat battery freeze protection
These features may be not available on all digital stats.

I thought in the 2 wire system, the wires get shorted or opened to turn furnace on and off.
I was thinking there is no power in the wires.
Thats why i was confused about a heating resistor living in the themostat asking for power.

So there is power in the two wires?

groundhogy wrote:
So there is power in the two wires?

afaik there is voltage in one wire but nothing flowing. When the thermostat connects the wires it sends the voltage signal to the furnace to get started.