He said he has received more than 15,000 messages since he decided to open up his business in Driffield, East Yorkshire, after reading about the plight of the homeless over the festive period.
Mr Woodhouse, who played for both Sheffield United and Hull City among others, said the messages have included inquires from people who needed accommodation but also scores of offers to help.
Now he said he is committed to offering a roof to help people at both Christmas and New Year and also providing a meal on the big day.
Mr Woodhouse, 38, said he had also been touch with the charity Raise the Roof, which said its plans to help 28 homeless people in Hull have been scuppered by the Royal Hotel after it cancelled its booking.
News of Raise the Roof's situation has prompted a rush of donations to its online funding campaign, and, on Monday morning, it was the most viewed page on the GoFundMe website.
Mr Woodhouse said: "It was a spur of the moment thing, really.
"I was walking over to the shop and I couldn't believe how cold it was.
"I started to think about homeless people and I could not get my head around how people are going to be living outside here, in the fifth richest country in the world."
He added: "I was sat there thinking that I've got this big building which is closed over Christmas.
"It's sat there doing nothing when people haven't got a roof over their heads.
READ: 'Room for improvement' on homelessness, West Yorkshire PCC says"Now I've had 15,000 messages. I think I'm going to need a bigger gym. It's restored my faith in the human race."
Mr Woodhouse was a professional footballer, before switching to boxing, becoming British light-welterweight champion.
After retiring from the ring he returned to football and was manager of Bridlington Town.
He said he is looking forward to helping out at the gym with his family and other volunteers, and hopes his three children will learn valuable lessons about Christmas from the experience.
Mr Woodhouse said he had been overwhelmed with the offers of support he has received, including a taxi firm that has offered to ferry people from Bridlington and Hull to the East Yorkshire market town of Driffield.
He said the gym will be open to anyone who needs it on December 24, 25 and 26 and again on December 31 and New Year's Day.
Mr Woodhouse said he is still looking for help with someone with experience of local bureaucracy as there may be "red tape" ahead.
His move comes as The Raise the Roof Homeless Project, in Hull, said it needs a "Christmas miracle" after the Royal Hotel cancelled its booking for 14 twin rooms with no explanation.Organiser Carl Simpson said he booked the rooms in the city centre hotel but, with only a week to go before Christmas, he has been told the bookings have now been cancelled