I have a friend who wants a radiator adding to his system in the garage. His proposing teeing off the 10mm pipe drops to the rad. Behind the garage wall in the kitchen. How big will this be heat wise? It's a new build so all piped from a central manifold in 10mm and can't really get to it to repipe. Thanks. The rads are 1000 by 600 in garage and I think kitchen a tad smaller.