I have a new garage with a radiant system that I fired up late last winter. Garage is 900sqft and is well insulated and has 2" under floor and on walls of foundation. I have four loops all around 270', 6" centers on exterior and 9" everywhere else. System works well but I have a higher delta T than what most suggest is optimal. I am using a tankless heater set at 110F. Temp in garage is set at 50F and slab temp is 55F. When systems fires up return temp is initially 55F and rises to approx 67F after about 20 minutes. I have approx 0.55gpm per loop for a total of 2.2gpm. Any ideas as to why the delta T is so high?