ThermalSheet Insulating Underlayment Frequently Asked Questions

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Should I add insulation before installing electric floor heating and how will that affect the system's performance?

When installing electric floor heating over a concrete slab, an insulating underlayment like ThermalSheet is highly recommended to ensure efficient operation, faster heating times and warmer floor temperatures.

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How many square feet of floor heating can be connected to one thermostat?

One thermostat can control multiple heating mats/cables as long as all the heating elements are using less than 15 amps:

TempZone™ will cover aprx. 120 sq. ft. for 120V systems and 240 sq. ft. for 240V systems on one thermostat.

Environ™ will cover aprx. 150 sq. ft. for 120V systems and 300 sq. ft. for 240V systems on one thermostat.

Slab Heat will cover aprx. 90 sq. ft. for 120V systems and 180 sq. ft. for 240V systems on one thermostat.

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Is a floor heating underlayment always required?

No, an underlayment isn’t always necessary. 

However, there are some situations in which the use of an underlayment would be required, such as heating over a cement slab (where an insulating underlayment would most likely be required). When heating over a cement slab, our recommendation is to use ThermalSheet as your underlayment. 

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How are insulating underlayments different from uncoupling membranes?

Insulating underlayments and uncoupling membranes share some key characteristics like providing crack isolation benefits, but they are separated by their primary functions.

Insulating underlayments, like WarmlyYours ThermalSheet, provide a thermal break between a subfloor and the heating elements, which can help prevent the concrete from acting as a “heat sink” and increase energy efficiency. ThermalSheet has a 1.5 R-value, and it offers crack isolation of up to ¼”. This can be particularly beneficial if you are trying to heat a room above a cement slab or above an unheated garage. 

Uncoupling membranes, like the Prodeso membrane, are great for protecting relatively fragile floor coverings like tile from foundational movement. They also allow for faster installation times than many other types of floor heating.

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Which floor heating underlayment is best for a high-moisture installation like a bathroom?

Typically, an uncoupling membrane like Prodeso will be best for this application because it can be paired with accessories to effectively waterproof the subfloor. 

However, if you have a cement subfloor, then ThermalSheet synthetic cork is a good choice because of its high 1.5 R-value and moisture resistance. 

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Do I need to adhere the ThermalSheet underlayment to the subfloor when installing an Environ heating system with a floating floor, such as laminate?

No, for the installation of an Environ heating system with a floating floor like laminate, it is not necessary to adhere the ThermalSheet underlayment to the subfloor. The underlayment should instead be allowed to float freely on the subfloor. Make sure to stagger adjacent sheets of underlayment and tape them together to prevent any overlaps, ensuring a flat and even layer beneath your flooring. This method helps accommodate the natural expansion and contraction of the floating floor.

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What underlayments are compatible with the Environ Heating System?

Installing Environ™ under wood laminate flooring requires a suitable underlayment beneath the heating elements. Never install Environ™ between two hard surfaces. Underlayments that are less than 2mm in thickness and that are not Robinson-rated are not acceptable. Underlayment is necessary to prevent Environ™ Flex Rolls from damage due to the weight of the floor, furniture, and people. Unavoidable wooden floor movements will not harm Environ™.

Installing Environ™ under carpeting(USA only) requires a suitable cushion/pad beneath the heating elements. Never install Environ™ between two hard surfaces. Carpet padding must have a density of at least 6 pounds per cubic foot, the higher the R-Value the better. 1/2“ Prime Urethane (R-2.15) and 1/2“ Bonded Urethane(R-2.1) are good choices. Adhere to Restrictions on Furniture Placement outlined on page 12 of Environ Install manual when installing under carpeting.

Environ™ must not be installed in direct contact with concrete, it is mandatory when installing over concrete to use a 1/4“ (6mm) Robinson-rated underlayment.

Certain underlayments, such as 1/4” (6mm) thick cork, or 6mm ThermalSheet are recommended for Environ™. It is also acceptable to place a vapor barrier, such as a plastic sheet, beneath the underlayment. Underlayment paper is not an acceptable underlayment choice.

Always check with the manufacturer of the flooring, carpeting, and underlayment for limitations and compatibility with electric radiant heating. Adhere to national and local code regarding electric radiant heating systems.

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What is ThermalSheet Insulating Underlayment and how does it compare to cork?

ThermalSheet Insulating Underlayment is a synthetic cork, a lightweight thermal barrier made of hemi-crystalline thermoplastic.

WarmlyYours recommends ThermalSheet underlayment when installing a floor heating system over a concrete slab to prevent heat loss and protect against moisture. It will not rot, support mold and mildew, or absorb moisture.

- ThermalSheet synthetic cork underlayment (6mm) has a 1.5 R-value, crack isolation up to 1/4“, reduces sound by up to 22 dB, and is Robinson tested (TCNA) and rated for residential loads.

- Cork (6mm) has a .72 R-value, crack isolation up to 1/32“, reduces sound by up to 23 dB, and is Robinson tested (TCNA) and rated for residential loads.

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Can LVT (Luxury Vinyl Tile), LVP (Luxury Vinyl Plank), or VCT (Vinyl Composition Tile) go directly onto the surface of ThermalSheet Insulating Underlayment?

No. Put a skim coat of SLC (Self-Leveling Cement), or even plywood over it first. Then, the vinyl flooring product can be installed.

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Do I need to adhere the ThermalSheet underlayment to the subfloor when installing a TempZone heating system with a fixed floor, such as ceramic tile?

Yes, ThermalSheet should be bonded to the subfloor with any high quality modified thin-set, or with a bond coat adhesive. Further installation information can be found in the installation manual. 

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