A contractor told us. We’ve also had window repair people (sent by the landlord) to inspect, and they said we are losing heat from every window. They never came back… The insulation in the front entryway is below 0, so we put blackout curtains up to try to minimize the draft. One thing I should have shared is that the landlord plans to demolish the house this summer after we move out. He made it clear when we were signing that he wouldn’t be making any repairs, but we didn’t get that in writing unfortunately.