About Radiant Insulation
Radiant heat insulation is installed to prevent heat loss from a PEX radiant floor heating system (most commonly, PEX embedded in concrete slab or stapled underneath the plywood subfloor).
Different insulation types help to minimize heat loss from convection (air circulation), conduction (direct contact) or radiation (energy waves) modes of heat transfer.
In slabs, insulation protects mainly against conduction heat loss, resulting from direct contact of the slab with the underlying level (i.e. gravel & sand). In frame construction, insulation protects mainly from convection and radiation heat loss.
Insulation R-value and ROI
R-value of insulation determines its’ effectiveness against heat loss and will vary (even for the same type of insulation) depending on the installation type, environment conditions and other factors.
For example, the same bubble foil type reflective insulation may have up to x10 times higher R-value when used in joist bays vs. when used under the slab. For this reason, only R-values for specific application can and should be compared.
ROI (Return On Investment) is a critical factor when deciding on insulation. The objective, in most instances, is to find a “golden middle” - i.e. select a product with optimal R-value and a reasonable price. Over-insulating may create a small difference in performance (energy savings), but will cost more and the savings will not be adequate to cover the added costs.
A study made by insulation manufacturer indicates than R-10 (2" XPS foamboard) offers as little as 6% difference in performance over their R-5.9 product. For comparison, the difference in price between R-5 (1" foamboard) and R-10 (2" foamboard) is 100%. In essence, nearly double the insulation costs twice as much and yet offers only a fractional difference in performance and energy savings.
Concrete insulation - foam board & blanket
Insulation is of crucial importance to a radiant heated slab with PEX. Without a thermal break between the slab and the ground, heat will sink into the ground under the slab, resulting in longer warm-up time, higher energy costs and overall poor performance of the system.
The two most commonly used types of insulation for under-the-slab installations are rigid foam board and blanket.
Rigid foam board is probably the most common and widely used insulation and has R-values which vary from 3.6 to 5.0 per 1 inch of thickness, depending on the raw material and production method. It is generally manufactured in 4ft x 8ft, or such as Crete-Heat, in 2ft x 4ft sheets.
EPS vs XPS foam board insulation - this debate has been long ongoing, with most recent data indicating that EPS is a more preferable choice, both cost-wise (evident from current market prices) and performance wise (based on 15-year in-situ study).
Pros:
- Best price/sqft.
- Great R-value retention over time (EPS only)
- Widely available in home improvement stores nationwide.
- Many thickness options (1/2", 3/4", 1", 2", 3", etc.)
- PEX can be stapled directly on top of foam (1-1/2” and thicker only). No stapling needed for Crete-Heat.
Cons:
- Permeable or semi-permeable to water, will likely require a vapor barrier (additional labor, costs).
- Easily damaged in jobsite conditions.
- Bulky, may be expensive to transport.
- Installation is time-consuming.
- Manufacturing produces a long list of chemicals (among them, HBCD) which are considered harmful to human health and the environment.
Blanket or multilayer concrete insulation is comprised of multiple layers of different materials, allowing to incorporate radiant heat insulation, conduction insulation and a vapor barrier, into a single product. R-values of blanket insulation vary greatly depending on the thickness, composition and order of materials used in its’ construction. Among the most common varieties of blanket insulation is bubble insulation, such as the one made by rFoil.
Pros:
- 2-in-1 insulation and vapor barrier (no need to purchase and install a separate vapor barrier).
- Large rolls are quick and easy to install – simply unroll and tape the seams.
- Compact, easy to store and transport.
- Robust construction, puncture and tear resistant.
Cons:
- Limited R-values, not designed to replace foamboard thicker than 1”.
- Unlike with foamboard, PEX tubing cannot be stapled over the blanket insulation - it (PEX) can only be attached to wire mesh or rebar in a reinforced slab.
Concrete insulation products overview
rFoil Ultra CBF is comprised of alumized reflective foil sandwiched between two layers of heavy-duty polyethylene bubble. Overall R-value of rFoil Ultra CBF is 3.8. It is intended to replace 3/4" or 1" thick expanded or extruded rigid polystyrene foam board when used for under-the-slab insulation. A 4ft wide x 125ft long roll covers 500 sqft area.
rFoil Underpad is comprised of two layers of polyethylene bubble sandwiched between the alumized reflective foil and the topmost thick polyethylene sheet. Overall R-value of rFoil Underpad is 1.1. While it does compare to foamboard insulation in R-value, it offers a basic and cost-effective thermal break & vapor barrier for slabs with low projected heat loss. A 4ft wide x 125ft long roll covers 500 sqft area.
Crete-Heat boards are made from expanded polystyrene with PEX holding knobs and have tongue & groove interlocking edges. They replace standard foamboard insulation and greatly reduce installation time and labor. Available in 1" (R-6), 2" (R-10) and 3" (R-15) options.
Between-joists insulation overview
rFoil 2222 series insulation is comprised of two layers of polyethylene bubble sandwiched between two outer layers of alumized reflective foil. It is designed for installation between the joists of a wooden frame construction where PEX tubing is stapled/secured to the bottom of the subfloor. Foil layers reflect radiant heat back to the floor, double bubble layer offers protection against conduction heat loss and when used with sealing tape, offers an effective protection against convection heat loss (from air movement). It is Class A/1 fire rated, mold-resistant and fiberglass-free.
Frequently Asked Questions:
Q: Do I need to install additional layers under concrete insulation?
A: For rFoil Ultra CBF and Underpad – No. Simply unroll the insulation and tape the seams per installation manual. The rebar/wire mesh with PEX tubing goes over the insulation and then concrete is poured.
For Crete-Heat, below-grade installations will require a vapor barrier. On- or above-grade installations may or may not require a barrier depending on the flooring type and local codes.
Q: Can blanket insulation be used together with (on top of or under) foamboard insulation?
A: In most cases, rFoil concrete insulation can be used in conjunction with rigid foamboard – but only when installed on top of foamboard. It provides an effective vapor barrier and increases overall R-value of insulation. You can contact manufacturer to ensure compatibility.
Q: Do I need to tape the blanket insulation at seams?
A: Yes, the insulation must be taped at seams. You can use 3" or 4" wide poly tape we sell or purchase a similar product elsewhere.
