Hi Sting, Hi Whistlenut.
Sting: I did put a piece of 'molded' flashing over the pex, stapled this long 'fin' to the subfloor, then insulate the joist spaces, I did an 'experiment' first.. a space with just pex, one with just the aluminum 'plate', one with foil faced insulation, and a space with the plate and insulation. The increase in floor temp was measurable. from the pex only to the plate and insulation was 10-11* warmer.. and most importantly,, the floor stayed warm for hours longer after the pex cooled off in the insulated joist space. Thank you for firmly suggesting that I add the aluminum fin/plate.. it was worth the money and effort.
Whistlenut: Thanks for the encouraging comments..[how did you know I was getting burned-out?
I have my AA260 out in a remote building, about halfway between my house and shop. I have burried PexAlPex to the house and shop.
I use the DHW coil in the AA to heat the floor in the shop. Since I have glycol in this system, I didn't want to mix it with the rest of the system's water. So it is independant from the house and boiler's water.
In the house I have a 40 plate water/water heat exchanger to transfer heat into the hot water heat system [s], then the water goes through a 30 plate water/water exchanger that preheats the cold water going into my DHW heater. Then the cooler water is piped back to the AA.
This system works fine if hot water is used at least twice a day, and usually it is, morning shower, and evening dishes and sometimes laundry. But when I'm not home, the DHW heater will fire and use some propane to keep the water at a minimum temperature.. I've always intended to add a small circulation loop to keep the tank/heater warm,, but my propane use is so little now, I'm probably not going to worry too much about it. If the DHW heater ever croaks, I'll probably put in an indirect water heater/tank. Or at least add a circulation loop when I install a new DHW heater/tank.
My coal use seems to be less than last year, but the weather this year is milder than last, so it's hard to say.. the house is MUCH more comfortable and consistantly warm.. the heat only cycles on a few times per day.. used to be a few times per hour. When it does cycle on, it runs for a longer period of time, since it has to heat the concrete suspended slab, but the slab then stays warm for many hours. I LOVE this hydronic radiant floor system !!