Designing a Radiant Floor Heat System
|Designing a radiant floor
heat system can be straightforward or very complicated, depending on
many factors. This guide is intended as a basic overview of the radiant
design process. Many variables are not addressed in this guide. We'll
be glad to help with your design and answer any questions, email
Step 1 Determine the number of zones.
A heating zone is one or more radiant heat loops (tubing) controlled by a single thermostat. Open areas (garages, basements, etc.) with one or more loops can be controlled by a single thermostat, but homes usually require multiple thermostats to control the temperature in the different areas effectively. Depending on the floor-plan, bedrooms can usually be controlled by a single thermostat located in the hallway outside the bedrooms; the kitchen, living and family rooms can usually controlled by a thermostat located in the center of these rooms; isolated master bedrooms and master bathrooms are usually controlled by separate thermostats.
Heat loss and floor type also play a significant role in determining the zone set-up in homes. Rooms with large heat loss due to numerous windows, poor insulation, northern exposure, etc., usually require a separate zone when adjacent room(s) have significantly different heat loss (fewer windows, better insulation, southern exposure, etc.). Rooms with carpet and hardwood flooring can generally be controlled by a single zone, but need to be zoned separately from rooms with masonry floors (tile, marble, etc.) due to the different temperature of supply water required. Common in radiant slabs, tubing spacing can be adjusted to compensate for different heat loss or floor type within a single zone, for example, closer tubing spacing for carpeted areas and wider tubing spacing for areas with tile. More zones always allows better temperature control and optimum system performance.
Step 2 Determine the number of tubing loops.
1/2" tubing is generally spaced 8" to 16" on center in concrete slabs depending on the design temperature, heat loss, floor type, flow rate and several other factors. Most living areas and office areas require 8" spacing, most basements and non-living areas including garages and warehouses require 12" spacing. Use closer spacing for the first few rows along the exterior walls. Closer tubing spacing has a higher installation cost, but allows for even heat distribution and helps minimize Hot-Spots and Cold-Spots (important for living areas, not so important for garages). For sub-floor installations with floor joists on 16" centers, 8" tubing spacing is required (two tubing runs per joist cavity). Tubing spacing over 16" is not recommended.
Tubing spacing multipliers:
Multiply the square footage by the spacing multiplier above to determine the tubing length for each zone. The absolute maximum loop length for 1/2" tubing due to frictional pressure loss is 400', but we NEVER recommend loop lengths over 300'. Shorter loop lengths work better because they provide less temperature drop in the loop. Hot-Spots and Cold-Spots become more noticeable with longer loop lengths. If your 1/2" tubing length is over 290 ft, divide the tubing length by 290 to determine the number of loops required for that zone (round up to whole number). Then divide the zone tubing length by the number of zones to determine the loop length. Make sure to add at least 10 ft to each loop for connecting to the manifold. For example: 575 sq ft area with 6" spacing. Multiply 575 by 6" spacing multiplier 2.0: 575 x 2.0 = 1150 ft of tubing required for the zone. Calculate number of loops: 1150 divided by 290 = 3.96, so round up to 4 loops. Divide tubing length by number of loops for loop length: 1150 divided by 4 = 287.5. The 575 sq ft area requires 1150 ft of tubing with 6" spacing in (4) 287.5 ft loops. Each loop needs an additional 10 ft for connecting to manifold, 5' per end (called "leaders"). Total tubing required for the zone is 297.5 x 4 = 1190 ft.
Step 3 Installation supplies.
Secure the tubing every 30" before pouring concrete. If you're installing 2" rigid foam-board under-slab insulation (recommended), use Screw Clips placed every 30" to secure the tubing. Screw clips twist into the 2" foam-board insulation then the tubing simply snaps into the screw clip. Divide your tubing length (feet) by 2.5 to determine how many Screw Clips to order (300' loops usually require about 4 - 5 (25) Pks. of Screw Clips). 8" Tubing zip ties can also be used to secure the tubing to the re-mesh or re-bar (available in 100 Pks).
You will need 2 slab risers (protective elbows), for each loop. Also, you will need a short length of protective sleeve wherever expansion joints or control grooves cross the tubing. (Protective Sleeve comes in a 10 ft coil).
Radiant Slab Rough-In Packs (PXOB3C3SRP) include Barrier Pex tubing and the supplies used for un-insulated slab installations. Radiant Insulated Slab Rough-In Packs (PXOB3C3SRPSC) include Barrier Pex tubing and the supplies (including Screw Clips) used for insulated slab installations. Radiant Slab Rough-in Packs are also included in Single Zone Radiant Packages for Concrete Slabs.
Step 4 Determine manifold configuration
HRFH manifolds can be easily configured several ways: 1) Single zone manifold with multiple loops 2) Multi-zone manifold with 1 loop per zone.
It gets tricky here...Questions? Email us at firstname.lastname@example.org
The single zone manifold can be used to by itself, or with other single zone manifolds to create a multiple zone radiant system. For a Single Zone radiant floor heat system, the circulator pump is usually installed directly to the manifold and controlled by a 110V thermostat (Single Zone Radiant Packages for Concrete Slabs are set-up this way). Multiple zone radiant floor heat systems are set-up the same way, just add a zone pump controller and 24V thermostats. Zone pump controller are sized according to the number of zones, for example, a 3-Zone system requires a 3-Zone pump controller (zone pump controllers are available in 1, 2, 3, 4 and 6 zone configurations).
The multiple zone/single loop manifold uses a circulator pump installed directly to the manifold, with loop actuators (manifold mounted zone valves) attached to each zone on the manifold, controlled by a zone valve controller with 24V thermostats. A zone valve controller can operate up to 6 zones. An alternate multiple zone set-up requires a circulator pump installed in the boiler supply line with a zone valve controller operating multiple motorized zone valves controlling the flow to multiple, single zone manifolds with 24V thermostats.
In most situations, both types of manifolds will work fine with one pump and up to 10 loops per manifold. For multiple manifold systems, all one type or a combination of both types, you will need to link the manifolds with your boiler supply and return lines.
Before you order your system, email the material list to us at email@example.com and we will review it to make sure the system is complete.
Note: Even though Radiant systems are very easy to install, we recommend installation by licensed, experienced professional installers. Radiant systems require electrical wiring, which must be comply with the NEC and other local electrical codes, if applicable. All electrical wiring must be preformed by a licensed electrician.
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