To install hydronic heating under the floor, plan the layout, install insulation, lay the tubing, connect to the boiler, and test the system for leaks.
Hydronic radiant floor heating provides efficient, even warmth by circulating hot water through pipes beneath your flooring. This guide covers everything from planning to final testing for a successful installation.
Planning Your Hydronic Floor Heating System
Proper planning ensures optimal performance and efficiency. Consider these key factors:
System Design
Work with a specialist to create a custom layout for your space. Companies like PexSupply offer free design services when you provide:
- Detailed floor plans
- Insulation values for floors, walls, and ceilings
- Your climate zone and heating needs
Zone Configuration
Divide your space into heating zones for better control. Common approaches include:
| Zone Type | Best For |
|---|---|
| Single zone | Small, open spaces |
| Room-by-room | Homes with varied heating needs |
Preparing the Subfloor
Vapor Barrier Installation
Start with a high-quality vapor barrier over the gravel base to prevent moisture issues. Overlap seams by at least 6 inches and seal all edges.
Insulation
Use rigid insulation (R-15 or higher) to direct heat upward. This is especially important for slab-on-grade installations where heat loss downward can be significant.
Piping Installation Process
Materials Needed
- 1/2″ PEX tubing (300-1000 ft rolls)
- 6×6 welded wire fabric (WWF)
- Zip ties or pipe staples
- 3/4″ PVC conduit for pipe protection
Pipe Layout Techniques
Follow these steps for proper pipe installation:
- Unroll PEX using a spool with wheels for easier handling
- Secure pipes to WWF with zip ties every 3 feet
- Maintain 6-12 inch spacing between pipe runs
- Use PVC conduit at wall turns for protection
- Label all pipe ends by zone for easy identification
Pressure Testing Before Pouring
Always test your system before concrete placement:
- Pressurize system to 50 psi with air
- Let sit for 24 hours
- Check for pressure drops indicating leaks
Concrete Pouring Considerations
Work with experienced concrete contractors who understand radiant heating systems. Key points:
- Minimum 4″ slab thickness recommended
- Use concrete with proper thermal properties
- Ensure even coverage over all pipes
Mechanical System Installation
Boiler Selection
Choose between:
- Standard water heaters (40-50 gallon)
- High-efficiency tankless units
- Dedicated boilers for larger systems
Pump Sizing
Calculate feet of head to determine proper pump size. The pump must overcome resistance from:
- Total pipe length
- Pipe diameter
- Number of zones
System Startup and Balancing
Air Removal
Use these methods to purge air from lines:
- Manual bleed valves
- Automatic air vents
- High-point vents in each zone
Temperature Balancing
Aim for:
- Supply water: 100-120°F
- Return water: 80-90°F
- Floor surface: 75-85°F
Maintenance and Troubleshooting
Common Issues
- Air in lines (most frequent problem)
- Undersized pumps
- Zone valve failures
Preventative Measures
- Keep spare pump on hand
- Install accessible isolation valves
- Use corrosion inhibitors in water
For complex installations or troubleshooting, consult the Uponor Engineering Handbook or a professional hydronic heating specialist.
