Winter is the best time to test for Radon Gas. Health Canada recommends a long term test of more than 90 days be done to avoid false high and low levels. Radon levels will fluctuate within your home day to day and even hour to hour.
Because Radon Gas comes from Uranium in the soil, it will always be present at some level where Uranium exists. The only way to protect your family is to test your home. Many homes have very low levels and may not require any corrective actions. Some however will have elevated levels and will require some form of mitigation. Without testing you can't know how safe your home is.
Testing is easy and inexpensive. Think of it as peace of mind. That is priceless !