ODR versus night setback thermostats

ODR versus thermostat night set-back

There are many homeowners confused with night setback and outdoor reset (ODR). The confusion is the use of night setback with the use of ODR becoming more common today. First let’s explain the difference.

Night Setback - This is when you manually or the thermostat automatically turns down the temperature of the home at night or when the home is unoccupied. Many years ago this was proven to be a fuel saver

Outdoor Reset - This is when a control senses the outdoor air temperature via an outside sensor and re-adjusts the system or boiler water temperature up or down to match the heat loss of the home and save fuel. As the outdoor air temperature gets colder the heating water gets hotter and as the outside air temperature gets warmer the heating water gets cooler. This may be better explained here.

Pro’s of Each

Night Setback

  • Most people like cooler air temperatures when sleeping
  • Can assist in saving fuel due to the fact that the closer the inside temperature is to the outside temperature you reduce the heat loss
  • When these thermostats became more popular in the seventies the manufacturer’s suggested up a 6% fuel savings

Outdoor Reset

  • Maximizes comfort by circulating cooler water around the home for a longer period
  • It is estimated to save up to 20% on fuel
  • Easy enough for the homeowner to fine tune control settings for their home

Con’s of each

Night Setback

  • Need more sophisticated thermostats
  • These were first introduced when houses were not as tight. The higher the heat loss due to requiring new windows, doors, weather-stripping, added insulation the more important night setback was. This was due to heat leaving the structure faster, by reducing the indoor temperature you would save fuel
  • The need for night setback for energy savings is less important due to tighter homes today.

Outdoor Reset

  • A need for another control with an outdoor sensor. The sensor needs to be away from sunlight, heat sources and above snow levels.
  • The interconnecting wire must stay away from power sources, magnetic field and any other electrical noise producing items. If not it will affect the reading the control sees on the outdoor sensor. The use of shielded wire will eliminate these problems. Shielded wire is a wire with a braided outer wrap, you unravel the metal shield and ground one end.
  • The use of ODR along with night setback thermostats will cause the warmup time in the morning or when coming out of un-occupied mode will severely be affected due to reduced heating water temperature. When the water temperature is reduced the heat output is reduced from the radiation.
  • Requires more homework to properly set up the control. Most are left at default settings.

2012 Compliance
On September first of 2012 the code changed. Some type of boiler reset will be required on all boiler installations. Even though this does not mean ODR I believe the use of ODR will become more of a common place at that time. This means to maximize the fuel savings OD reset parameters should be dialed in properly.

Night setback in conjunction with ODR

When discussing fuel savings this is normally not a good combination due to reduced water temperature in the baseboard. The recovery time may take hours and become very uncomfortable during the wait. Many ODR controls now have what we call a boost feature. This means the ODR will override the lower heating water temperatures by normally 10f at a time. This boost feature works on a timer. Every time the electronic timer times out, it will raise the boiler water temperature by 10f, until it hits boiler high limit. The down side of this feature is in multiple zone systems or slow reacting systems like radiant floor heating it will always be raising the system water temperature as it does not know the difference between one long heat demand or overlapping zone demands.
There are intelligent thermostats today that will learn how long it takes to bring the house temperature up and will actually start turning up the temperature much earlier. This will actually reduce the setback time. We have a few options that will still save us fuel. Since ODR will save us far more money that night setback and improve comfort better I would choose that ODR is more important than night setback. Either do not use night setback or limit the setback temperature to two to three degrees and use a thermostat that will learn how long it takes to bring the home up to temperature.

Disclaimer: The information found on this website is for informational purposes only. All preventive maintenance, service, installations should be reviewed on a per job situation. Any work performed on your heating system should be performed by qualified and experienced personnel only. Comfort-Calc or its personnel accepts no responsibility for improper information, application, damage to property or bodily injury from applied information found on this website as it should be reviewed by a professional.