The Stockton Shelter for the Homeless has 152 beds for single men, and another 25 rooms for homeless families with children.
But when temperatures plunge to freezing, extra sleeping mats go on the floor, and nobody is turned away.
Shelter Director John Reynolds says they've always been able to find room for those caught in the cold.
"Let's say there's a new family living in a van and they are going to be in the area, it gets cold, you want shelter, you want to come in, you're welcome," says Reynolds.
Many of those seeking shelter are living in tents, or cardboard shacks.
But Reynolds says even those living in cars aren't much better off in freezing conditions.
"Well if you try to sleep in a car when it's 20 degrees outside, or 30 degrees outside, it's like trying to sleep in a refrigerator," he says.
Reynolds says cold weather can bring as many as 100 more people to each shelter facility.