Economy Radiant Floor heat advice
I just designed and installed my own system. I installed tubing in gypcrete upstairs and concrete downstairs. Two zones run off two taco pumps, pump relay and two thermostats feeding 120 F hot water provided from a standard 55 gallon, 42,000 BTU water heater.
The system was far cheaper than any quotes I received and works very well. Non-oxygen barrier PEX is less expensive and may be use in a system without any cast iron or components that will rust. Installing tubing in gypcrete or concrete provides a significant buffer for minor errors in tubing design, length and spacing, and maintains a superior level of comfort. Your feet and sinuses will love it.
Alternatively, placing tubing between floor joists or beams requires higher temperatures (180 F) and is risky business, since wood strength, beam composition and floor glue are degraded by increased temperature over time. Check the specifications with your structural engineer regarding building material temperature ratings, including finished floor coverings.