heat-timer RSM Installation & Operating Instructions Manual

INSTALLATION/OPERATING INSTRUCTIONS

RSM

A Control for Under Slab Heating Systems

Used to Melt Ice or Snow

How the RSM works...

The RSM is designed to control under slab heating systems to prevent accumulations of ice or snow. To do this, it
monitors three temperatures, the outside temperature, the temperature of the fluid going to the slab, and the temperature
of the fluid returning from the slab.

The slab must be kept above freezing (32°F) whenever there could be frozen precipitation. Therefore, any ice or snow
which falls on the slab will melt immediately . If precipitation is allowed to accumulate before the slab is heated, an effect
called bridging can occur. The snow or ice directly in contact with the slab will melt. But the snow above will act as an
insulator, reflecting the heat back into the slab. The slab itself will be dry , but the remaining accumulation will melt very
slowly. To prevent this, the RSM activates the slab heating system whenever the outside temperature falls below the
adjustable outdoor cutoff temperature or whenever the optional external system starter is activated.

Once the slab heating system is activated, the amount of energy entering the slab is determined by the difference between
the temperature of the fluid going to the slab (the Slab Supply) and the temperature of the fluid returning from the slab
(the Slab Return). The difference between these two is called the ∆ (Delta)T or the difference in temperature. The ∆T will
be different for each slab composition. The higher the ∆T, the more energy is being input to the slab. If the ∆T is too
large, the slab itself can be damaged. The RSM provides a maximum ∆T adjustment which can be set from 5°F to 50°F

The RSM will control a 3-way motorized mixing valve to regulate the amount of heat being supplied to the slab. The
motorized valve will mix the heated fluid from the heat source with the fluid returning from the slab. As the slab or its
components can be damaged by excessive temperatures, the maximum temperature for the slab supply can be adjusted
from 70°F to 180°F. If the Slab Supply temperature reaches this limit, the control will immediately begin to close the valve.

Due to the twin constraints of maximum ∆T and maximum Slab Supply temperature, as well as the nature of under slab
heating systems, a typical slab will take many hours to reach melting temperatures. A 24 hour warm-up period is not
unusual. The RSM is provided with a Tune adjustment to insure the slab temperature will be sufficient to melt frozen
precipitation once the warm-up period has ended. The Tune value compensates for both different slab types and
different outdoor weather conditions. After making a change in the Tune value, it is necessary to wait at least several
hours before accessing what affect it will have on slab temperatures.

WARNING: This Heat-Timer control is strictly an operating control; it should never be used as

a primary limit or safety control. All equipment must have its own certified limit and safety
controls required by local code. The installer must verify proper operation and correct any
safety problems prior to the installation of this Heat-Timer control.

1

INSTALLATION

Mounting the control

• Select a location which is indoors, or which is protected from the elements. The control must be protected from
extreme heat or cold.

• The RSM is designed to mount on a standard 1900 (4" x 4") electrical box or can be flush mounted on a panel with the
extension skirt included.

• Before mounting, bring the power and load control circuit wiring into the 1900 box and connect to the individual wires
coming from the back of the control (See Wiring the Power and W iring the Output).

• Use the two screws provided to mount the RSM to the 1900 box.

Installing the sensors

• All three sensors are interchangeable.

• The sensor wires can be extended up to 500' by splicing with two conductor 18 gauge wire. Do not run wires in

conduit with line voltage.

• The Outdoor sensor should measure approximately the same outdoor air temperature as the slab will experience.
Therefore, mount the sensor away from any doors, windows, exhaust fans, vents, or other possible heat sources.
Keep the sensor out of direct sunlight. Locate the sensor on the north side of the building or in a similarly shady
location.

• The Slab Supply and Slab Return sensors must be installed in 3/8" ID immersions wells (HT #904011 or equivalent).

• The immersion well for the Slab Supply should be put in the fluid going out to the slab, approximately 10' past the heat
source.

• The immersion well for the Slab Return should be put in any convenient location where the fluid has returned from the
slab.

Optional

System Starter

Motorized

Valve

Heat

Source

TYPICAL INSTALLATION

Outdoor

Sensor

Slab

Pump

Slab
Supply
Sensor

Slab

Return

Sensor

2

Wiring the Power

• Attach line voltage to the two orange wires extending from the back of the RSM.

• Use wire nuts, or wrap the connections with electrical tape.

• Class 1 voltages must enter the 1900 box through a different opening from any Class 2 wiring.

Wiring the Sensors

• The sensor wires have no polarity . Either wire from a sensor can be connected to the appropriately marked RSM screw
terminal (see below) or the sensor common marked COM.

• Either or both screw terminals marked COM can be used as the sensor common. They are interchangeable.

• The two wires from the Outdoor sensor must be connected to the RSM front screws marked OUT and COM.

• The two wires from the Slab Supply sensor must be connected to the RSM front screws marked SUP and COM.

• The two wires from the Slab Return sensor must be connected to the RSM front screws marked RTN and COM.

Wiring the Output - Heat Source

• The RSM has one set of Normally Open (N.O.) dry contacts (blue wires) to activate the heat source for the slab.

• The N.O. contacts do not output power. They simply switch power through the circuit.

• If the heat source will be active whenever the RSM will activate the slab heat (as would be the case if the heat source is
also used for space heating), connect the blue wires in series with the power for the slab pump.

• If the boiler for the slab heating system has a dedicated pump, simply connect the blue wires in series with the limit
controls of the boiler so that both the boiler and pump start.

• If the boiler and pump for the slab must be energized separately , use the blue wires to ener gize an external double pole
single throw (DPST) relay. Attach one set of external relay contacts in series with the slab pump power. Attach the
other set of external relay contacts in series with the limit controls of the slab boiler.

• The RSM contacts can switch 10A, 1/8 HP at 120V. If the slab pump or boiler requires more power , an external relay
must be used.

Outdoor Sensor

Slab Supply Fluid Sensor

Slab Return Fluid Sensor

= Supply Temp
= Return Temp
= Target

T

= Slab

∆

= Supply Limit
= Cut-Off Temp
= Tune

OUT SUP RTN COM EXT COM

WIRING DIAGRAM

OUTPUT

UP
PRESS TO READ
DOWN

To Optional
External Starter

Blue

Blue

Red

White

Black

Orange
Orange

N.O. Contacts

Activate Heat Soure

Valve Motor Common
Valve Motor Open

Valve Motor Close

120VAC Input

3