RTGs get hot, that's the point of them, actually. Too hot for use in a small area like your fridge. On a space probe or rover on a cold planet, the waste heat is useful in keeping things somewhat warm. On earth, not so much.

RTGs are also large, too large to power a fridge given the power draw for a fridge. There were microRTGs used in some pacemakers, but the long term safety concerns were never overcome.

The decay rate is high enough that you'd need to augment or refuel your house every handful of years. Halflife of 87 years, 25% energy loss in 40ish, 10% loss in just over a decade, etc.

Also, they've got little plutonium pellets in them, which is both expensive and dangerous.