Apologies if this is a stupid question--I just want to make sure we are being as efficient as possible: I live in central PA--hot summer, cold winter, and definite seasons of spring and fall. Our geo system was installed in May and we got through the summer great, but now that fall is really here I am unsure how the thermostat should be set. We are currently having days in the 60s (nice for open windows and fresh air) but nights that go down into the 40s (so need a little heat). I have two zones upstairs and one down. Right now thermostat is set at 67, which feels comfortable enough, but the heat is definitely kicking on as my house seems to hold at 65 or so with no heat or AC running--this seems chilly, esp. to the skinnier people in the family. :-) Am I supposed to turn the system off completely in the spring and fall? If not, what do I do if I want to open windows? Or if I only need heat upstairs during the night, but not during the day? We want to be comfortable, but not throw money away at the same time. Thanks.

Great question! I'm in SE Pa, with the same experiences. I tend to just shut the system off for days at a time, and if I turn it on because it's extra chilly, I try to make sure it's not set too much higher than the current indoor temp so as to avoid Aux coming on. You could leave the upstairs thermo/zone on at a decent temp, but shut off the downstairs thermo. There will be some mixing and heat transfer around though when the system comes on for one zone or the other.

Depending on your thermostats, you might want to experiment with Cycles Per Hour, or possibly an outdoor lock-out sensor. Different thermostats and zoning panels have different options, but you might be able to interrupt calls for heat and/or cool with an outdoor sensor. I know sometimes a morning can start off cool but warm up and it's sorta pointless for the system to come on, especially if I had windows open at night for the fresh air. Manual shut-down is really the only way I can think of.

Another definition of throwing money away, might be spending 5 figures on a system to stay comfortable affordably..........and then not using it to stay comfortable. Just saying

As long as you don't operate the system at the same time as having more than a couple windows open, you should be OK.

The whole idea of investing in geo is the return obtained by very low operating costs.

Don't worry...be comfy.

Thanks for the replies. I think some of my concern was coming from a situation where we had no central AC (just a few window units) last summer/fall and an electric bill @ $100/month total, to this summer/fall having the bill be more like $220/month total (this has been very consistent since the system went in, and yes, we have been much more comfortable), and thinking we have doubled our bill. I know the real test will be the winter months, when our electric bill last year (for upstairs heat plus lights, cooking, etc) was over $400/month PLUS regular oil bills for the downstairs heating averaging $600-700 every 4-5 weeks. And this was keeping the thermostat set at 66!

This may be an example of the "licensing effect" caused by aquiring energy efficient property - knowing that the equipment is efficient causes it to be used more.

Folks with tankless water heaters sometimes take much longer showers...

Honeychurch,
Did the window units take care of the whole house, or just select rooms? I mean, are we comparing cooling the *whole* house with window units vs the *whole* house with geo-a/c? Also, take into account that PA had one of the wettest followed by one of the hottest summers (or maybe it was other way around) in history.

I'm like you with the heat, though. My 1.5 story cape ate $500/month year 'round in oil/hot water baseboards, then the regular electric use on top of that. Now the most it's been (2 winters in a row) is $280, but usually around $200, and I know about $100 of that is regular (non-heating/cooling) use. This year, we ripped the roof off, rebuilt the 2nd story, and put insulation in (there was very little previously).

Re the shoulder seasons, I, too like to open windows and leave them open overnight, not worrying if the house gets a little chilly or a little warmer. I like to experience some variance inside the house, so the system is switched off on both thermostats, often for weeks.

If your winter oil bill was $600/mo, your first expenditures should have been aimed at improving the outer shell of the building, by air sealing and insulation, before looking for a cheaper way to counter an enormous heat demand. A well-insulated house will lose or gain heat far more slowly in the shoulder seasons and make temperature control much less problematic.

Two months before the geo system was put in, we did insulate the whole house (cellulose blown into exterior walls and attic, foam sealing in basement and attic, new storm doors, weather stripping, etc--house is from the 1800's and had practically zero insulation, so it is much improved!). We knew it would be useless to install any sort of new heating/AC system without doing this first.

House is 4000 sq ft, and those window units were in each of 5 bedrooms, a family room, and a den---the bedroom ones really only ran at night, and the other 2 during the day.