What is an outdoor reset and how can it save me money?
An outdoor reset device helps save energy on hydronic heating appliances, like boilers or solar thermal systems, by adjusting the temperature of the water being heated based on the outside air temperature to make sure it’s only as hot as needed.
Hydronic distribution systems spread heat by piping water to different zones of a home, for example, the bathroom, kitchen, or bedrooms. The heat can be emitted using radiant floor slabs, radiators or baseboards–each requiring different water temperatures to provide adequate heat to a room. Radiant floors require the lowest temperature water, between 90-140°F. The range for radiators is typically 120-180°F and for baseboards 150-180°F. The specific temperature depends on the layout of the emitter, how well a home is insulated, and the thermostat setting. The appliance’s control system ensures water is supplied at the correct temperature. When it’s warmer outside, the heating appliance runs for a shorter amount of time because the home isn’t losing as much heat to the outdoors.
An outdoor reset control allows the water temperature to vary based on the outdoor temperature. On mild days, the water temperature is lowered so the appliance can produce less heat. When it cools off, the outdoor reset raises the water temperature to compensate. This allows the heating appliance to take advantage of longer run times no matter what the temperature, reducing the inefficiencies of cycling on and off.
Think of an outdoor reset as allowing the heating appliance to drive on the highway instead of in stop-and-go traffic. Outdoor reset can also prevent overheating that could result from high water temperatures in mild weather.
Finally, to add a little physics to the mix, delivering a lower water temperature to the heat emitter means that the water returning to the appliance is also lower, increasing the efficiency of heat transfer (using less fuel!)
Many heating appliances now come with outdoor reset controls, and they can be retrofitted onto older appliances as well. If you want to learn more about using outdoor reset to save energy, talk to a mechanical contractor to see if it would work for you.