My insurance company told me I needed a fresh air intake for my Tarm Solo 60. The boiler is in my attached garage and I built a 6'x11' boiler room around it with 5/8" firecode plasterboard and a steel fire door to the room. I was thinking about using 4" PVC from the attic down into the boiler room. Could I then use a U trap and then go back upwards. I have heard many different options ,but i dont know what is the best. My garage is not airtight anyway so I dont understand how much air I need? Can I just stub the pipe in the attic or do I need to pipe it out the soffit? Is 4 inch too big or small? Should I put a gate valve in the pipe?