Many Hot Yoga Studios struggle in cooler times to achieve the ideal temperature and humidity in the yoga space.
Insulation is the most important aspect of heating and making simple additions like installing stretch window plastic over windows and even doors can make a big difference . I would even use foam sheets over windows to isolate the glass as it is your biggest loss. Buy a infrared thermometer gun to test surfaces-keep in mind it is only accurate 3 feet or closer from the surface. once you locate your cold spots you can insulate with curtains and any other materials to stop losing heat.
Humidifiers- Keep in Mind that it takes 1000 Btu to convert water to a gas and That Means it absorbs HEAT. So if you use a misting or even warm misting humidifier you are losing heat. Only Steam Humidifiers can produce Humidity without losing Heat.
Cheap humidifiers are not Steam Humidifiers and if you used 3-4 -10 of them you are cooling your room as they cool the air up to 40 degrees.
Las Vegas and other arid areas use them for outdoor air conditioning!
Use a towel or make a door slider to insulate under doors and be sure to use insulating gaskets over door frames.
Don’t waste heat be kind to the earth .