Messages and Online Forum Q&A

Re: Heating Granite Countertops

From: katie_neben@yahoo.com
Category: Kitchen
Remote Name: 70.59.36.172
Date: 16 Nov 2005
Time: 08:05 PM

Comments

Question: We are installing new granite countertops. An acquaintance recommended that we look into running electrical heating under the granite to keep the counters from being too cold. Do you have any experience with whether or not this is effective, practical and worth the time and money? Thanks in advance. Living in the land of Kitchen Remodel DUST!

Builders Websource® Answer: We've been asked about radiant floor heating, but this is our first request for heated countertops! The good news is, the same engineering principles that apply to radiant heat under a floor can be applied to heated granite, stone, or tile countertops. Before getting into the details, let's focus on your last question first: is this practical and does it make financial sense?

The answer depends on your priorities, your budget, the type of home you're building, the extent of the surface area you want to heat, and the climate in which you live. Certainly heated countertops are very rare and would considered an ultimate luxury for some or a complete waste of time and money for most. While it's true that stone countertops feel cool to the touch, many people prefer this cool feel (you know it's real stone). If you live in a moderate climate, our opinion is that heated countertops are unnecessary as well as a wasteful use of electricity. You certainly won't score any points with the eco-conscious.

Furthermore, if you also have stone or tile floors, focus first on using radiant heat on the floor before considering its use on countertops. Radiant heat on the floors in kitchens and bathrooms is a very comfortable heat that keeps your feet warm and the floor free of excess moisture.

Any natural stone material such as granite or marble, as well as synthetic materials such as concrete countertops, have significant "thermal mass." This means that these materials have the ability to store heat, creating a memory effect based on the average ambient temperature over a period of time. Eventually, the temperature of the stone's surface will be at equilibrium with the surrounding air temperature. If you live in a very cold climate, the feel of a granite surface might be uncomfortable to you in the winter, particularly if the heater has been off during the day. It could take an hour or more to adjust to the room temperature when you return from the office.

Another angle to consider is possible health-related side effects of a heated countertop. Countertops are notorious breeding grounds for bacteria, particularly in the kitchen. As single wipe across the counter with a dirty rag (even one that looks clean) may spread harmful bacteria across your work surface. A warm countertop will only exacerbate this breeding ground, creating an ideal environment for exponential, accelerated multiplication of bacteria, resulting in unintended food poisoning or illness. Bacteria such as salmonella and e-coli which are often associated with contaminated poultry, beef and unwashed produce could live longer on a warmer surface, hence posing a higher health risk to you and your family. With the right mix of contaminated food, moisture, and warmth, bacteria can double every 20 minutes. The "danger range" for bacterial growth is 32 to 149 degrees F. The cooler the surface, the slower the reproduction rate will be. And while low temperatures won't kill bacteria, it will slow its reproductive speed.

Now, let's suppose that you toss our advice out the window and that you're willing to endure the wrath from your energy-miser neighbors next door. You've decided to be a trendsetter and be the first on your block (and probably in the whole city) to install a heated countertop. There are two ways to approach this. First, you could use PEX radiant heat tubing as part of a circulating hydronic radiant heating system. This would only make economic sense if you were installing a larger hydronic system for whole house heat. More likely, you would use an electrical heating wire embedded in a fabric mesh--the same type commonly used under floors.

While there are many manufacturers on the the market, we like a product called ThermoTile™ from Thermosoft International Corporation. It comes in 15" wide rolls (about the right width for a 24" countertop application) and is only 1/8" thick. Since the radiant heat generally extends only 1-2 inches from the edge of mesh, you may want to place it slightly towards the front edge of the countertop since this is the portion of the surface you'll be touching most often. That means the rear portion may not feel as warm, but who cares if you're not touching it. ThermoTile™ can be conveniently embedded in the thinset mortar between the mortarbed/backboard and the granite or stone without adding excess height to your countertop (typically the countertop surface should be approximately 36" above the finished floor). If you really want to get fancy, you could also mount foil-faced foam insulation under the plywood countertop (foil facing up) to help reflect heat back through the granite.

Not all radiant heating mesh is created equal. Some innovative features we like about ThermoTile™ are noted on Thermosoft's website and are reproduced here for convenience (see http://www.thermosoftinternational.com):

• Double insulation to protect the heating cable during installation and use
• Double ground protection - offers 100% ground coverage
• Double EMF (electromagnetic field) elimination
• Double overheat protection comprising patented FiberThermics® heating elements
• Protective outer Nylon sheath resists abrasion and corrosion
• PVC insulation provides double protection and is UV resistant
• Inner foil cover eliminates EMF (electromagnetic field) & provides 100% ground protection
• Ground wire assures safety
• Insulated return wire maximizes installation convenience and cancels EMF
• Insulated Heating cable comprises patented, FiberThermics® electro-conductive fibers with temperature-self-limiting/thermal cut-off overheat protection
• Special cross-linked polymer sheaths protect FiberThermics heater & return wires and can withstand -50°C to +200°C
• Limited Lifetime Warranty to the original homeowner when installed in accordance with manufacturer's recommendations

Electromagnetic considerations are not insignificant. An improperly installed system or poor choice of vendor could result in a giant antenna in your kitchen, possibly interfering with TV's, radios, cell and wireless phones, or other electronic devices that are sensitive to electromagnetic interference (EMI).  Please note that Thermosoft does not specifically endorse or recommend the use of their product in this application. However, from a purely engineering viewpoint, there's no fundamental difference between use on a floor...and use on a countertop in terms of the engineering principles of radiant heating.

To control the temperature, you'll need a thermostat/regulator and a dedicated circuit breaker (20-30 amps most likely) to supply power to the system and for safety reasons, the system should also be on a GFCI (Ground Fault Interrupter Circuit) to prevent accidental shock hazard in the event of a short. The programmable thermostat from Thermosoft includes an integrated GFCI as well as 120/240 operation. Follow installation instructions with precision.

For installation examples, see: http://www.thermosoftinternational.com/thermotile_example_installations.htm for additional information.

If you decide to move forward, we urge you to contact Thermosoft first for further recommendations or considerations before you go down this path. And, as to materials cost, figure on spending between $500 - $1000 for a decent sized kitchen, plus possible added expense of running a dedicated electrical supply line from your circuit breaker panel. Electrical consumption is approximately 12 watts per square foot. To put that in perspective, 20 lineal feet of countertop (assuming a single 15" width) will draw approximately 360 Watts, or the equivalent of nearly four 100W light bulbs.

Let us know what you decide and may your kitchen dust go away soon!

Builders Websource®

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