Changing thermostat

[CJreef]

I am replacing a wall thermostat with a new model for a hydronic electric baseboard. The wires on the new thermostat are cleary marked load and power. My problem is I don't know which of the lines to the old thermostat is the load and which is the power. Can I assume that the power always comes from the top of the box and the load goes out the bottom? Thanks.

[jimbrown]

NO. If you have a multi meter you can check to see which ones are hot, thats the power, and the other ones should be the load.

[CJreef]

Thanks for replying. I guess I'm out of luck without a meter [img]/forums/images/icons/frown.gif[/img]

[RichZ]

You can buy a cheap multi meter for a job like this. It certainly would be worth it, to hook up the thermostat properly. You can get a cheal one at Harbor Freight for under $10. It'll be good enough for this job.

[eccentricfarmer]

Yes the meter is a good thing around the farm and should be part of a basic homeowner kit. I think the little sensors that tell if there is power in the line are even cheaper if that is an issue. I like using that better if just chasing a line and looking for a break. But then in a pinch i have been known to use a LITE BULB for a tester.

[Pat]

I have several meters, some expensive and the cheapest a Harbor Freight digital pocket sized that cost about $3 which is plenty good enough.

If you disconnect the suspected load wires and have voltage to the other wires then they are the ones getting power from the breaker. Don't test for voltage using your tongue. Get a cheap meter or alternatively get an outlet tester, the kind you plug into an outlet to see if it is powered up and wired correctly. Also get a couple alligator clip leads. Attach one end of each clip lead to one of the prongs on the tester. If you clip the other ends of the clip leads to the wires under test AND there is power a light will light up on the tester.

Maybe one of the SMART GUYS can tell me what difference it makes which way you connect a direct power switching thermostat. Isn't is just a switch that closes to apply power and opens to shut it off?

Pat

[jimbrown]

Pat My guess is that for just a simple thermostat It probably makes no difference except that if wired wrong the parts inside of the switch (springs ect) would probably be hot as opposed to just one contact. Not that one should be touching them anyway. Now the thermostats in my house are probably critical on the polarity as they probably got more electronics in them than a 10 year old computer does.

[Pat]

Jim, Since a simple thermostat is just a switch once it's contacts are closed both sides are at the same potential so it would only be "safer" on the one side when the contacts were open.

My house is on a zoned system (9 zones) and I have 8 complex programmable thermostats. Several of the zones have simpler but still not plain old fashioned heat activated switch type thermostats mounted next to the more complex ones. Some of the zones have either in ceiling or in floor hydronic heat and all zones have forced hot or cold air. Some zones have hydronic control only thermostats and some have hot/cold air only and of course several have both.

The electricians who wired a thermostat in our sitting room installed the wrong stat. It was to control a fan in a duct to draw hot air from the sitting room ceiling and blow it into the master suite entry area. This was to help prevent overheating of the sitting room while running a decorative propane fired gas log parlor stove. (Sitting room is all ICF construction walls and can be heated with a candle and cooled with an ice cube.) They got a nice Honeywell stat that went open on heat rise instead of what was needed, one to give contact closure on heat rise.

I installed another Honeywell stat in the sun room to control the exhaust fan. I wired it with a center off double throw switch so the fan can be on thermostat control, forced to run no matter what, or turned off no matter what. When I get caught up a bit on projects I'd like to put an electrically controlled 2 position damper on the outlet of that exhaust fan. One position would exhaust the hot air into the attic near the ridge vent (current configuration) and the other position would route the exhausted air into the great room which would let me use the solar heated air of the sun room to help warm the house.

Now I have enclosed the open side of a shed to make a metal working/welding shop on the side of my garage/wood working shop and will be extending the HVAC out into that area. More electrically controlled dampers and stats to install.

Pat