Options for Radiant Loop on Gravity Boiler

rdhMN

I know there's a thread on this, but I have a few specific questions.
I have a 1929 2-story tudor with the original gravity boiler - 4 cast iron radiators on each floor. 2 main loops coming in/out of the boiler. No heat in the basement. I'm adding a basement bathroom. Was planning on electric in-floor heat but ripped out enough concrete that it makes sense to lay pex in the new slab. I'm using 1/2" HePex. My heat load will be small - in the 6-8k range. Maybe smaller if I can get enough foam under the slab. I love the gravity boiler. It's quiet. It works. It's just really old.
There's a good chance I'll replace the boiler in 3-5 years. That said, I'm trying to figure out how to heat the pex in the meantime. I don't want to invest much in it. I'm thinking about trying a Taco 003 circulator on the end of one of the cast iron legs to circulate water through the 130' of pex and back (single loop). Roughly 100' of that will be in slab. I would use a floor sensing thermostat to limit the floor temp and a strap-on aquastat to activate the pump only when the water temp is high enough (when the water is moving around). Seems like the mains risks are: (1) water temp too high for in-floor radiant (2) low GPM and head pressure due to low BTU load makes it hard to choose a pump, but I need to keep it slow (3) balance on the gravity boiler system being thrown off.

If it doesn't work, I suppose I'll add a mini boiler or just wait for a new boiler. Any other ideas? Ideally, any equipment I invest in could be re-used in a new boiler setup. I was even thinking about using a 12' section of cast iron pipe on top of the main supply trunk as a heat exchanger so the pex would be its own closed loop.

lefty1cad

We are doing an exterior loading dock. We wanted to do a reverse return radiant heat pex piping system the dock is 84' x 12' is it feasible.

Paul48

@lefty1cad ........You should start your own thread.