FAIRBANKS — The “Ask a Builder” series is dedicated to answering some of the many questions Fairbanks residents have about building, energy and the many other parts of home life.
Q: What is an outdoor reset and how can it help me save fuel?
A: An outdoor reset is a device that helps save energy when using hydronic heating appliances, like boilers or solar thermal systems. The outdoor reset adjusts the temperature of the water being heated by the appliance based on the outside air temperature to make sure it’s only as hot as needed.
Hydronic distribution systems spread heat by pumping water through pipes to different zones in a home. The heat can be emitted using radiant floor slabs, radiators or baseboards.
Each requires different water temperatures to provide adequate heat to a room. Radiant floors require the lowest temperature water, 90 to 140 degree Fahrenheit. The range for radiators is typically 120 to 180 degrees Fahrenheit and for baseboards 150 to 180 degrees Fahrenheit. Several factors determine the actual temperature needed — the layout of the emitter, the insulation level of the home and the thermostat setting.
There are a variety of appliances that are compatible with hydronic distribution systems: boilers, solar thermal systems, and ground source heat pumps, to name a few.
In a typical system, the temperature of the water is determined by the heating demand of the home, the thermostat temperature and the distribution method. The control system for the appliance 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 has to produce less heat. When it gets cold, 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, delivering a lower water temperature to the heat emitter means that the water returning to the appliance is also lower, which increases the efficiency of heat transfer (using less fuel!)
Many heating appliances are now sold with outdoor reset controls, and older appliances can be retrofit with them 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 with your heating system.
Ask a Builder articles promote home awareness for the Cold Climate Housing Research Center (CCHRC). If you have a question, contact us at firstname.lastname@example.org or 457-3454.