I live in a two story house with a basement (some call this three story) and I think the whole house is around 3600 sq. ft. I have one 28 year old thermostat and heat pump to heat the entire house. There's some type of auxiliary heat that cycles on and off if the outdoor temp. is below 40. The auxiliary heat is more expensive because it uses some type of electric heaters.
Typically, during the winter, I have the thermostat set so the downstairs is around 64-66 with it dropping as low as 62 on a particularly cold night here on the east coast. Upstairs is anywhere from 66-70, depending on the room. The NE side is about 66-67 and the SW side varies from 67-70 depending on if the door is open to the room. I don't know what the basement is as I don't use it. These temps. are fine for me and I wouldn't mind if it were a little bit colder.
My December electric bill is usually around 1750 kWH and January is the highest at around 3180 kWH ($315). I figure holiday baking and oven usage plays a part in that. It's also usually colder in January too. February is often in the middle at around 2300 kWH.
This year is totally different. My Grandma lives with me now and she freezes if it's 76 in the middle of summer. It was 38 outside this morning with the indoor temp. at 70 and she was cold with layered clothing plus a blanket.
Is there a way to keep the downstairs warm and keep the upstairs cold? I tried shutting most of the vents upstairs while opening nearly all of the vents downstairs. But I'm not sure this is wise. If cold air sinks, maybe I should open all the vents in the house. I don't know.
Then I think maybe I should open the downstairs vents, shut the upstairs vents and put up a curtain at the bottom of the steps to help keep the cold air upstairs. It would look silly, but if it works then maybe it's worth it.
Grandma is supposed to pay the difference in heating costs, but I'm still afraid of the bills. I'm 99.9% certain I'll have to buy two space heaters (one for Grandma's bedroom and one for the living room), but I'd like to figure out where my thermostat should be set first to keep the heating costs as low as possible.
Any suggestions?
I don't think I want Grandma to use electric blankets because she has incontinence, especially at night. She sometimes wets her bed and she wears those adult diapers all the time. So I don't feel comfortable with her using electric blankets. If I get space heaters, I'm leaning towards the oil kind as I heard they're the best (most efficient and economical). Even though Grandma wears layers, she still gets cold. She often complains of her fingers being cold. I don't want to have her wear gloves, that doesn't seem right.
I'll also point out that I don't think my heat pump and/or duct work is very efficient anymore. Most houses of this size are now being built with two or three heat pumps and thermostats.