i just put radiant heat on the my first floor and i love it. i put 3 zones in. two of them are less than 100 square feet, and one is about 500 square feet. my 2nd floor has old fashioned radiators, 3rd floor has nothing right now.
anyways, the rooms warm up nice (and i haven't even insulated the joist bays yet ) but i noticed when i go in the basement and feel the pex loops (i put in pex between the joists with transfer plates), all of them get fully up to temp except for the return on the larger loop. my house is almost 100 years old. it's a pretty darn long loop for the living/dining room. it doesn't really bother me that much, but i'm curious as to why that return isn't heating up fully on the one loop. i'm using a taco mixing valve and a 007, with 3 zone valves. i'm not using a manifold with metering gauges because i figure that the 1st floor will be self-correcting, although some zones may heat up a little quicker. but even when i only run the big zone by itself, the return only gets up to probably 100 or so, whereas it's supply is 140ish. the other zones get even return and supply temps. maybe it's losing some heat as it gets to the end of the loop?? maybe insulating the joist bays with reflector and r19 would help?
i guess this long loop is just too far away from the boiler (in linear pipe)??? maybe it should have been two loops?
thanks for any input!