I know there was a post awhile ago about the pro's and cons of turning down the thermostat on a geothermal at night. We have a snergy 3d. Dh likes to keep the upstairs at 72 f during the day and 69/70  at night. Night being from about 9pm to 7am. We keep the radient downstairs set a 72 all the time. We are in Ontario, Canada about an hour  north of Toronto. Our hydro bill is running between 112 to 125 kwh per day, that for all hydro and electricity for 5 people. Hydro bill seems high to me. What does everyone thing of 1, turning down the heat at night, and 2 the amount of hydro we are useing. Our aux heat has never came on, and I barely use the dryer. Also our area is going on time of use hydro soon. Any way to save heating and cooling costs with time of use.

There might be some benefit, but if not managed carefully, use of aux heat during recovery will more than exceed any setback savings.

Need to know more about size of your system to judge if power consumption is overly high

I'm not a pro. When you go on time of use rates I wonder if it would be worth it to heat an additional buffer tank for the radiant system (assuming your geothermal system has capacity to spare) so the stored heat can be used during the day? If so, I would think you would need a tank with extraordinarily low heat loss, like a Marathon with claimed 5f heat loss per day.

Depending on the size of your geothermal system in relation to your heating needs, you may not have spare capacity when it is extremely cold outside, but you may have some capacity when it is a little milder. I hope someone more knowledgeable than I can refine this idea, if it is practical.

what is the size of your system? what was your calculated heat loss? Do you have a baseline for electric use,maybe before you went geo? Right now I like your setback strategy.

Assuming an average COP of 3, you're delivering ~36.8MMBTU of heat/month to the house, which is a credible mid-winter number for a non-superinsulated not super-tight house in your climate.

Turning it down at night only to have the auxilliary kick on during the AM recovery period isn't saving, it's losing. (The resistance heat has a COP of 1). But a setback of only 2-3 degrees F isn't buying you much when the delta-T between indoor/outdoor temps overnight is 70-80F. The change in heat load on the affected zones with a tiny setback is less than 5% and you're pumping at least half of that loss back in. If you made it a 10F setback it would be more substantial, but the aux heat would likely kick on and blow away any savings.

Turning it down 3 degrees F and LEAVING it down will result in saving in the mid-single digits of percentages.

If the daily use is 120kwh/0.4MMBTU, and more than half of that is used during standard-rate hours, it would take a very substantial buffer tank to store half the heat during the off-peak hours. Since the off-peak hours also correlate highly with peak load hours, the "excess" capacity on the geo during those hours is also not likely to be very high. But it would take a lot more system and loading profile detail to be able to say if/when/how-big a buffer should or could be useful. (Not a "design by web-forum" kind of task.)

Agreed, most systems have excess capacity most of the time. So most of the time, you would have some capacity to heat up a buffer tank during off peak hours. Exactly how much would take some calculations.

The second issue is a tank - something like a 8'x8' polyethylene tank may or may not fit for you.

A tank would be useful for night setbacks or any time you want to bring the temperature up quickly without causing aux heat to kick in.

If you just want setback and aux never kicks in anyway, just disconnect the aux heat.

It's the age old trade off of comfort vs. savings. Yes, you can save energy/money by turning the system down at night, provided of course the aux/backup heat is disabled. The lower you turn it down at night, the longer the system will take to recover to what ever your comfortable temperature is.  Generally the acceptable length of time for setback is at least 8 hours, any amount of time shorter than that, really isn't saving all that much.   When I was setting my heat back, I was turning the heat down at 10pm and not turning it up until 4pm the next day during the weekdays. (bedtime and hours at work) The addition of a Parrot to the family prevents me from experimenting with the heat anymore.

My system (4 ton GeoMax2) in my house (2100 sq feet, not super insulated) seems to do better when the thermo is not set back more than a few degrees at night/daytime when we're asleep/out. Any more and the unit either takes forever to warm up the house (with aux disabled) or happily turns on aux to make up the difference. I've been keeping the downstairs at 70 when we're about, and 67 at night/work, and upstairs 67 in the morning and evening, and 65 day/night.

Personally, I think my unit is slightly undersized for my house/insulation level, but I'm working on correcting the latter of those two things.

I think I remember a fairly long thread on setbacks some months ago. Some very intersting observations were posted on setbacks, recovery, and impact on the ground loop temperatures with aux heat enabled or disabled. For example... I was suprised to read when using set backs there can be cases where disabling the aux heat could actually cost more!

When I installed my pump and dump system, I ordered the unit with no aux heat, and I've never needed it. Thanks to countless tubes of caulk and spray foam the heating load was quite a bit less than I had been told to expect, which is a good thing. As a result, my compressor rarely runs on second stage. Because the system is open loop and oversized, we can get away with more agressive setbacks. We have fairly quick recovery and maintain steady efficiency regardless of the how long the unit runs due to constant entering water temperature. Pump energy and cleaning my heat exchanger every fall are the downsides to my open system, but this spring will be 2.5 years and it will have already madeup the upfront cost difference over the alternate (high effiicent propane furnace).


I would love to figure out a cheap way to lower the pump energy. I'm using about 850 watts to pump 3 gpm up to 65 psi or more, only to let it bleed out back to zero down the drain.

We have 6 tonne waterfurnace snergy 3d. 3000 feet of horizontal pump. No pre existing data because this is a brand new house. The only reason we turn it down at night is it seems to hot for us. We are heating about 4500square feet. Thats the whole house

For a 4500sf house, an hour north of toronto, with a six ton system. 125kw a day for total electric consumption in the heart of winter sounds pretty good. Did your installer give you any projected operating cost data? I would watch your consumption in shoulder seasons to see how much elec the rest of the house uses.

My thermostat controls my main level (in floor radiant).     It is set to come on at 67 and off at 70 (24/7).     I guess once it hits 70 it lets the floor keep heating and then at 67 kicks back on and draws from my 50 gall buffer tank.    The tank usually cuts off the heat pump when it hits around 112f and kicks on the heat pump at 101f.   Seems to work well..  I did think about a programmable Tstat and do the set back thing. (had that with my hot air LPG system (very $$$ way to heat)).  I do not think I will play with dropping it back to 65 at night.   It takes almost 2 hrs for the room to get from 67 to 70 when it is 28F outside.  If I am away for a couple of days or so, I do kick it back to 65.  Which means it will keep the temp in said room between 63 and 65