Can Setback Thermostats Save you Money?
What does a Setback Thermostat Do for a living?
Programmable Thermostats can be set up to automatically change the temperature setting depending on what you have programmed them to do. Most often Setback Thermostats are set to reduce the temperature during the night when everyone is warm in bed, or when people are out of the house.
When the programmed time to bring the temperature back up is reached, the thermostat triggers and the temperature increases.
Some Setback Thermostats can control the air conditioning and the reverse happens (this is called Set Up!) The house air conditioning is reduced and the temperature is allowed to go up when no one is there
Savings can be significant.
What are the savings if I set back my thermostat?
The Institute for research in Construction tested several different levels of setback for heating and set up for air conditioning. They maintain 2 identical R2000 test houses in Ottawa.
Even in highly efficient houses, the savings were noteworthy. Savings of up to 13% in furnace gas consumption and over 2% in furnace electrical consumption were observed.
The highest saving occured at the lowest set back temperature, (6 degrees C. below "normal" temperature of 22 degrees.)
The greatest savings also occured when the temperature outside was lowest AND the weather was cloudy so that there was no solar heating through the windows.
On warmer winter days, savings from thermostat set-back were not good, as the R-2000 home maintained its temperature even if the thermostat was lowered since the furnace didn't have to come on anyway. Less well insulated homes would show increased savings in such case.
It took longer for the house to warm back up (called the recovery time) from its cold setting when the weather was colder. This reduced the saving a bit because the thermostat had to be put up earlier. This reduced the amount of time the furnace was kept less busy.
If the furnace is of lower capacity, the recovery time can be very long and savings reduced.
What are the savings if I keep my house warmer in Summer?
Two strategies were tested. One was to allow the temperature to rise when people were out, then cool the house again when needed in the evening.
The Second more successful strategy was to keep the temperature constant but set warmer.
The savings in both cases is very dependant on the amount of sunshine. In periods of high sun and therefore high heat gain savings are increased.
letting the temperature rise then cooling it when needed resulted in savings of 11% over the season.
Recovery time, the time it took to reduce the temperature, can be as long as 7 or more hours on hot days, reducing the saving. Another problem is that the Air Conditioner would be working hardest in the evening high peak demand time.
A superior strategy was to consistantly keep the temperature warmer. Air conditioner and furnace electrical savings were more than twice the savings. They added up to 23% over the cooling season.
Unfortunately, reducing the use of air conditioning increases humidity and perceived temperature.
In the case of Air Conditioning, the best strategy is to strike a balance between comfort and savings.
The report by the Institute for Research in Construction is interesting but a bit heavy reading.
So What do I do?
Reducing the temperature by 4 degrees Centigrade at night and during the day when no one is there will save you money. Reducing the temperature too low will increase the risks of condensation and moisture problems.
The longer the temperature is kept low, the greater the saving-- No surprise there.
In summer keeping the temperature consistantly warmer will result in the greatest saving
Nick Boothby, Maddy Dennett and Greg McDowell
REALTORS® / Salespersons
Christine DeMerchant Unlicenced Support Person
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