I’ll talk in general terms so please do your own research or check with me for more info about certain plants. I am talking from a Sydney perspective so you may have more or less humidity, or higher or lower winter temperatures.
Most indoor plants are from a more tropical environment and so prefer a more humid space. Heating and air conditioning remove humidity from the air so there are a few things you can do to help reverse that. Putting plants in a glass cabinet where you can use a small humidifier, putting the pot on a saucer of pebbles with a little water in it, grouping plants together as they create their own microclimate that way, using a large humidifier to make your plant room more humid. Remember too that you may have to move plants that are too close to a heater, fireplace or are in the path of air conditioning heat.
Being that most indoor plants are from a tropical environment they also don’t like colder temperatures. It is best to research individual genus of plants as some are alright with temperatures down to 10 degrees celsius or lower but some definitely aren’t. I have a Cissus dicolor and it will die if the temperature goes below 15 degrees or below 50% humidity. Some plants are hardier and so I know I can leave some of my Syngoniums and Epipremnums outside in a Sydney winter (undercover but not in a greenhouse) but I’m taking most of my philodendrons into the greenhouse.
WAYS TO HEAT PLANTS:
Well, not heat the plants, but protect from cold. I have a few methods that I am using. The most precious and tropical are in glass Ikea cabinets with grow lights above and an oil heater next to the cabinet to keep them warm overnight. These include Cissus discolor, Piper crocatum (ornatum), Philodendrons like melanochrysum, Majesty, verrucosum, etc. A heat mat with a grouping of pots on it should work too, just make sure the humidity is there too (could be a mini greenhouse or near a humidifier). A heat mat will only benefit the plants that sit on it. It’s not a reliable way to heat anything bigger than a small cabinet or mini greenhouse.
I then have most of the plants in a greenhouse outside with shade cloth in it so they don’t get the full sun, but the warmth during the day, and a heater in there at night with a thermostat that turns on when the temperature drops. The greenhouse also has a vent in the roof with an automatic arm that opens when the temperature rises so it provides a fail safe so the plants aren’t cooked, and air flow with the vent drawing excess heat out.
LIGHT & WATER:
Don’t forget that light in your house will change from Summer to Winter. Make sure that there is still enough light getting to your plants and if not, then move them or invest in grow lights. Right next to or touching windows will be quite cold though so keep an eye on that.
Water your plants less in winter, or at least check before you water. They will be growing slower, and might be getting less light so having their soil drenched will promote root rot with all that cold wet soil. Less heat will equal less evaporation of water from the soil.