How to Reduce Energy Costs with Weather-Based Heating Controls
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How to Reduce Energy Costs with Weather-Based Heating Controls

A description on how to install a hot water temperature reset controller on your boiler to reduce home heating costs.

If you heat your home with a hot water baseboard heating system, you can reduce your home heating costs this winter by installing controls which sense the outdoor air temperature and raise or lower the water temperature based on the reading. These controls are commonly referred to as Hot Water Temperature Resets.

How Hot Water Temperature Resets Work

Under normal conditions, boiler systems heat water to a preset without taking into account the outside conditions. Since the system is meant to keep the home warm during very cold temperatures, the discharge water temperatures must be sufficiently high so as to compensate for actual heat loss. This temperature is usually between 160 and 180 degrees Fahrenheit. The problem with setting the water temperature this high for the anticipated colder days, you are wasting energy on milder days. In engineering terms these are referred to as “Design Days”, the days when the outdoor temperatures are as cold as they will be and the unit is sized and set to maintain comfortable indoor temperatures. Fortunately design days only account for about 5 percent of the time; the other 95 percent of the time the temperatures are milder.

Many boiler manufacturers offer hot water resets with their equipment as an option, high efficiency models may even have them included. But if you own an older boiler, all is not lost, you can retrofit your boiler with a reset controller to start saving anywhere from 10 to 30% in your home heating costs. The simple payback is 1 to 3 years.

Installation Considerations

There are three main components to a hot water temperature reset; the outdoor sensor , hot water temperature sensor, and the controller.

The outdoor air temperature sensor is basically a thermometer that is connected to the controller by way of a simple thermostat wire. The sensor typically uses on two of the wires, so you should run 4-wire thermostat wire. (Why not 2-wire thermostat wire you ask, well what if one of the wires gets damaged later on or you want to upgrade the sensor to one that uses 4 wires; you won’t need to run a new wire. Plus the cost is practically the same)

The installation is fairly simple, but you should use caution when working with boiler controls and low voltage wiring. Turn off the power to the boiler and verify that there is no voltage present with a volt meter. Follow the instructions provided by the manufacturer and you shouldn’t have any problems. The installation should take about 2 hours.

• Mount the sensor on the North side of your home. It cannot be in direct sunlight or it will not read the air temperature accurately.

• It should be away from any heat source such as a dryer vent or chimney.

• You can mount it near an air conditioning condenser since this will not be running in the winter.

• Don’t install the sensor too close to the ground, especially if you receive heavy snowfalls. The temperature under the snow up against your house will be warmer than the air temperature.

Basic settings are included with the control. The reset process is linear so if you set the end points it will control the boiler temperature in a straight line. For example: Set the start point at 55 degrees outside air temperature and 120 degrees for the hot water temperature; then at 10 degrees outside air temperature use 180 degrees for the hot water temperature. This will give you a reset that looks like this:


  • Drill with ½ inch drill bit long enough to get through your siding on floor joists.
  • 1/8 inch drill bit for pilot holes in the boiler shell.
  • Wire Strippers
  • Screwdriver
  • Electrician’s Pliers

Installation Steps:

  1. Use a ½-inch-diameter bit to bore a hole through the exterior wall and into the basement.
  2. Feed the thermostat wire through the hole to the outside.
  3. Make the wire connections to the rear of the control's base.
  4. Screw the base to the house, and then snap on the cover.
  5. At the boiler: Secure the control's temperature sensor to the hot-water pipe leading out of the boiler with a cable tie.
  6. Cover the sensor with foam-rubber pipe insulation.
  7. Mount the control to the side of the boiler by drilling 3/32-inch-diameter pilot holes through the sheet metal of the boiler’s shell and attach the control with sheet metal screws provided.
  8. Hook up the wires at the outdoor reset control, including connecting wires from the outdoor control and to the boiler sensors, and wires that carry voltage to the control and to fire the boiler.

Typically, you leave the old controls in place without removing them, but the wires from the rest controller will take the place of the wires from the aquastat that was used to set the temperature before.

Overall, installing a hot water temperature reset is on of the easiest ways to cut your energy costs when heating your home with a hydronic system. The pump will run a little longer since you are circulating cooling water, but you increase comfort and reduce the amount of fuel you use.

Additional resources:

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