Will I save energy by lowering my thermostat at night?

Ryan Peterson May 1, 2018Updated: July 30, 2020

I have a 1500 sq ft home just north of Toronto, Ontario. I recently installed a cold climate air source heat pump furnace.  I am getting confliciting information about temperature control. Is it best to set the ASHP furnace at one temperature all day?  Or set it back at night and during the work day?

Responses (4)

Ryan Peterson 4 years ago

Thanks Mike! 

My home was built approximately 1975.  The best I can tell, the walls are insulated with R12.  I recently had a Home Energy Audit and found that my home has 6.5ACH at 50 pascals.  Providing I performed the "recommended" upgrades for air sealing (which I am in the midst of) it is estimated that my ACH will drop to approx 5.89ACH.  It was also recommended that I upgrade the ceiling and the finished basements (always cold) insulation - which I will in time.  The windows (double pane) and doors are all Zone 2 rated appear to have been replaced within the last 15 years.  I have only been in the home since the end of Feb, but from then to mid April it seems the house was dropping from 20C at 9pm to ~17C by 2am when the ASHP came on to maintain by set overnight temp.  I have no thermal mass in my home; floors are either carpet or laminate and the exterior is aluminum siding over the orginial tougne and groove wood siding.

I have had 3 HVAC contractors in my home for assessment.  The first, said to set it at one temperature and forget - stating ASHP are the most efficent at one consistant temperature.  Second contractor, said because my Zuba is a 3 ton unit (with time scheduling including capacity limiting) and the house is a little under 1500sq ft (easy load for a 3 ton) I can turn it back at night during cold months but one temp for summer because removing humidy is hard.  Third contractor said the exact opposite of the second contractor.

Totally loss on what to do.

Ecohome 4 years ago

Between the conflicting advice you’ve been given by contractors I’d stick with ‘set it and leave it’. That’s not a great amount of insulation and it’s fairly leaky at 5 + ACH, so it’s possible you’d see savings but it’s still sort of splitting hairs. It’s true that a reduced differential between inside and out means reduced heat loss, but at the same time, maintaining a constant environment is how a heat pump works best.

For longer absences you’d probably save by moving the thermostat, but for day to day operation I’d just leave it where you’re comfortable, if anything just for the lack of hassle compared to the minor savings if there even are any. And there is always the possibility that the end result of your thermostat wrangling could actually be a bit higher cost, and a less comfortable home at times.

Same thing for the summer – unless you're leaving on vacation for a week, set it, leave it and don’t sweat it! The best savings are had by keeping the temperature a bit higher in the summer and lower in the winter so you’re not fighting nature as hard.

Ryan Peterson 4 years ago