Baseboard-Heater Thermostats

Warning! Warning! Warning!

The Barclay wall-mounted heater thermostats handle the full line voltage and current supplied to the baseboard heaters (208 Volts AC, at up to 20 Amperes).

You want to skip all of this reading and go directly to preparing your shopping list?

Use of any electronic thermostat avoids the wide temperature swings common with mechanical thermostats. Try this with your mechanical thermostat: turn the temperature-selection knob slowly back and forth, making note of the difference in temperature readings when you hear the click on the way down, and on the way up. These dials are deliberately imprecise, but you will see that the difference is several degrees. From an energy point of view, this wide swing is wasteful because to prevent the room temperature from dipping into the "discomfort zone", the temperature must be set higher than for a thermostat with tighter temperature control.
The Advantages of an Electronic Thermostat

There's some interesting reading from Hydro Quebec, found here. There is even a "List of Eligible Thermostats", which is especially interesting if you also have property in Quebec, and qualify for a subsidy to replace your thermostats! From a previiously-available web page:
Image showing advantage of using an electronic thermostat

Technology
Pro
Con
Notes
Mechanical sensor and switch Relatively inexpensive Allows wide swings in temperature, easily 7 degrees Fahrenheit, forcing a higher set-point to avoid temperatures dropping into the "discomfort" zone. This wastes energy. Original Barclay thermostats used a bimetallic strip to sense temperature. "Bulk Buy" retrofit employs a "double-bellows" as sensor, and a microswitch for power control (giving that "click" sound).
Electronic sensor, and relay for power control Tighter temperature control: temperature regulation can be +/-0.5 degrees C around the setpoint. Relay allows higher power handling (typically 20 Amps) than a totally electronic unit. More expensive than the mechanical thermostats, often is four-wire, requiring knowledge of which wires are "supply" and which are "load" (baseboard). The Aubetech TH110-SP series is the only known model at this time. It employs a 15 minute "Cycle Time" (see bottom of this page).
Electronic sensor and power control

(keywords are "TRIAC" and electronic switch)		 Tightest temperature control (+/-0.15 degrees Celsius), greatest comfort, silently "pulses" heater on for a few seconds at a time, keeping it "warm", and seldom hot. Safest for children, pets, furniture etc. Higher cost, restricted to lower power loads than a relay model (maximum current handling is about 16.7 Amps). These usually employ a 15 second "Cycle Time" (see bottom  of page). Using the Fahrenheit mode gives finer control than use of Celsius, assuming the manufacturer allows one degree increments in both cases.
Programmable

(available in both "relay" and TRIAC models)		 Greater energy savings achieved by lowering the unoccupied temperature. Some have only "day" and "night" periods; others also allow lowering the temperature on weekdays while you are at work. These are more complicated because there is a clock to be set, day of week settings, and statutory holidays to be accommodated. Some also have a "vacation" setting: while you are away the temperature is maintained at a constant lower setting (day and night) for greatest energy savings.


Selecting a thermostat presents a slight mathematical challenge because most off-the-shelf packages assume a 240 volt environment when quoting Watts. Some give you a hint of the problem in selecting a thermostat for 208 volt operation by saying, for example,  "4000 Watts at 240 volts or 2000 Watts at 120 volts".

A significant parameter of interest is the current-handling capacity (measured in Amperes or "Amps"). Continuing with the above example, the manufacturer might also say "Current rating 16.7 Amps non-inductive (or resistive) loads only". This is 4000 / 240 = 16.67 Amps (Watts / Voltage = Amps).

A "TRIAC" is an electronic switch, used both in light dimmers and baseboard heater thermostats. Light dimmers "chop" the power going to the incandescent lamp load on both halves of the 60 Hz cycle turning "ON" at 120 times per second), at any point on the sine wave, from zero to the maximum line voltage. (The TRIAC turns "OFF" when the current drops to zero, also at 120 times per second.) The "hot-switching" or turning "ON" at a non-zero voltage often causes Radio Frequency Interference (RFI) heard in telephones, sound systems, and especially AM radios.

When controlling higher-powered loads such as in a thermostat for baseboard heaters, "zero-crossing detection" is employed to turn "ON" the TRIAC when the voltage and also  the baseboard heater current is very close to zero. This reduces the RFI and necessary filtering to its minimum. The heater output is "modulated" by selecting a time period (such as 15 seconds) and turning the heater on for only a portion of this period. E.g. if the micro-controller in the thermostat determines that only 20% of the heater's potential heat output is required to maintain the room at the selected temperature, it will turn the heater on for only 20% of the (15 second) period. I.e. the heater in this case would be "ON" for three seconds, and "OFF" for 12 seconds, repeating this pattern until a change in demand is detected.

When the heater  is controlled in the above manner, it stays warm to the touch, getting neither hot nor cold.

"Editor's Choice"


Aube Technologies

Aube Line-Voltage Thermostats

Why buy an Aube Thermostat? They're the cleverest I have found, and best for use in the Barclay, having the highest-rated TRIAC models. They turn our baseboard heaters from a "vice into a virtue".  Proportional control of the power going to the heater has these advantages:
Clever Baseboard heater thermostat

The best selection of Aube products was formerly found at Rona (Merivale Road // Hunt Club).

As of October 2005 Rona appears to be stocking the TH104, TH106, and TH109 models, but not at all stores. See Rona

As of December 2005 "You will find these units in Quebec (without special order) because electric heating is more common there". Try the Rona at 165 Boulevard du Plateau in Gatineau (Phone: 819-776-3400).
(Revised Fri Dec 2 16:14:15 EST 2005)
Aube Model #
 Rating at 240 Volts
( Current in Amps)
 Total Watts at 208 Volts
(e.g. Barclay use)
 Program-
mable?
TH108* or TH109*
(TRIAC)
 3000 W / (12.5 Amp)
 2600
 No
TH104** (TRIAC)
 3500 W / (14.5 Amp)
 3030
 Yes
TH101** or TH106
(TRIAC)
 4000 W / (16.67 Amp)
 3467 (see disclaimer
for use at 3500 Watts)
 Yes
TH110-SP (relay)***
 Formerly 4800 W / (20 Amp), now 4000 W / 16.7 Amp
 ~3500 Yes

* The TH108 presents an "uncluttered" face - the temperature up/down buttons are camouflaged. For buttons that are obviously temperature up/down buttons, choose the TH109.

** The TH101 and TH104 are not recommended for Barclay use, being more suited for cottage application.  They may be found to be more difficult to program, and embody a mode which if chosen, reduces their temperature-regulation performance from +/-0.15C to +/-0.5C

*** Aube offers a line of 20-23 Amp "relays" (TRIAC with 15 second cycle-times and electro-mechanical with 15 minute cycle-times). These are controlled by a low-voltage (24 volt) thermostat, which necessitates a 24 volt transformer. These rquire an extra effort to install in the Barclay: Both the supply (from the breaker panel) and load (the heaters) wiring meet in the present 2" x 4" thermostat box. A TRIAC relay would require surface-mounting to a new 4" x 4" electrical box, and space would be required for the 24 v transformer, unless it were built-in to the relay.
An electro-mechanical relay unit could be mounted within a baseboard heater, but a means would have to be found to get the control signal to it from the thermostat: running the contol wires using the technique used for running telephone wires to an "extension-phone" may be permitted since these wires would carry only the 24 volt control signal.

Confirm what the total load (Total Watts at 208 Volts) will be for a thermostat you intend to replace. E.g. where the thermostat controls two heaters, is it 2000 + 1500 = 3500 Watts, or 2000 + 1750 = 3750 Watts, or ... ? Get onto your knees and with a flashlight look inside at the righthand side of the heater (no disassembly is required). Write down the information - e.g. "208 VAC 2000 Watts".

Disclaimer: Running at 3500 Watts means running an Aube "4000 Watt" thermostat at about 1% above its stated capacity.

Should you take the chance and do it?
From private communication with Aube:

"Our thermostats are tested and are approved at CSA. The TH106 is approved at 16.6A but it will also work at 20% above its capacity without trouble. ... So physically it will work, it's just a matter of approvals."
These are the highest Wattage units I  have found, from any manufacturer, to use a TRIAC or "electronic switch". Engineers always design in a "safety margin". If you wish to be conservative and not run at 0.95% above capacity , use a TH110 (relay unit) to control a 3500 Watt load, and for any larger loads.

I have installed Aube TH106 thermostats in two locations, both controlling a total of 3500 Watts. They have operated flawlessly since installation in October 2003 (over 3 years to date in Feb 2007). Notwithstanding my "luck", the decision is yours.

Higher Wattages (e.g. 3750, or 4000) will require a relay to switch the power. The relay emits a "click" as it turns on-off, and because it operates on a 15 or 20 minute cycle, temperature regulation is +/-0.5 C, versus the +/-0.15 C for the TRIAC models. The TRIAC allows fully silent operation (no "click" of a relay), and a finer proportional control (modulation) of the power delivered to the heater.

Note: the relay units, despite being capable of handling higher power, are physically smaller than the TRIAC units. This is because the  latter  embody a "heat sink" for the TRIAC. A TRIAC unit running at or near its maximum rating is noticeably warm, but this is normal.

Programmable Thermostats too Complicated for you?

Don't worry. They all have a manual mode. When you feel brave enough to try "programming", and you don't get it right at first, you can always retreat to the manual mode until your next try.

News Release:

HONEYWELL ACQUIRES AUBE TECHNOLOGIES

"MINNEAPOLIS, September 7, 2004 - Honeywell (NYSE: HON) today announced the acquisition of privately held Aube Technologies Inc., a leading designer and manufacturer of line volt thermostats based in Saint-Jean-sur-Richelieu, Quebec. Financial terms of the purchase were not disclosed." Go to this location for more information.

Other Manufacturers

These are presented in the interest of completeness/fairness. The features and power-handling capacities fall short of the Aube product line, and are largely unsuited for use in The Barclay.

Honeywell t4700 example (will handle 3325 Watts at 208 Volts)

Honeywell Thermostat look-up (if you know the Honeywell model number, you can look it up)

Cadetco is Honeywell supplier? (It's the t4700, with "Cadet" written on the front instead of Honeywell)

UPM Marketing (units will handle up to 3120 Watts at 208 Volts)
The heat delivered is a function of how long the heater is on in the period. For  a TRIAC unit, the period is 15 seconds, while for relay power control this period is typically 15 minutes.

Heat Delivery Controlled by "Duty-Cycle"