Heated Granite Counters

JudeNY

I hate the cold feel and would like to heat the island overhang where the two stools are. The cabinets will be frameless so there is no space between the counter and top drawers.

While I am installing pex in Thermofin to heat the floor, I was thinking I could pull the pex through the floor into the sink base (no plates under the island) switch to copper with shut off valves then back to pex and get it to the overhangs, then back to the floor. I was thinking to put in a bridge and shut off valves so if there is a problem with the counter heat I could continue to heat the floor.

Then it started sounding too elaborate and maybe not a good idea to have a floor loop coming up to heat the counters. It's not worth it to run a separate loop for the counters. Can I heat the counters with electric mats ? Can I get the mats in a 1'x2' size.

jerry scharf

I've seen it done with electric

My favorite tile store reps nuheat. They have the electric heater under a granite slab as their order counter. It's great to lean on the counter and talk to the sales guys. They say it's just great for convincing customers on how nice it is and they have gotten a ton of sales for doing that. Maybe some of the wallies can use the trick.

I think either of the solutions has some flavor of the same problem: How do you mount the heat source under the overhand in a way that is safe, effective and good looking?

jerry

JudeNY

jerry, I checked out nuheat, Wattsradiant and WarmlyYours and they all specify their mats only for under the floor in thinset. I was thinking to spot glue the net under the overhang, cover with rigid insulation and trim with cabinet molding. But I do not know if that is safe. Do you know how your tile store rep did the installation ?

Mike T., Swampeast MO

The electric mats

I believe they overheat and burn out if not fully embedded in a highly conductive substance like mortar.

If the overhang is integral to the rest of the top I believe it will heat quite evenly even without a heat source directly under that area. Granite conducts heat rather slowly, holds a lot of heat and when polished has quite low emissivity. A horizontal, flat surface isn't too good at enhancing convection Those properties should combine to keep the temperature of a polished granite slab fairly even in temperature despite an uneven heat source.

jerry scharf

what I know about it

The tile store granite had the heater in thinset. The wires are subject to high heat if not installed according to the manufacturer specs. I went with the mat and thinset for the one place I used this and it worked out well.

I wasn't going to say it becuase I'm not an expert, but I was thinking exactly what Mike said. Heat the granite under the supported part of the slab and it will conduct the heat to make it all feel nice.

I'm not sure that picking up the floor loop would do it. It seems like a completely different amount of time to heat up the slab, etc. That's just a guess, I love reading the posts from those who really know what they are doing with all this.

jerry

Mike T., Swampeast MO

Quite some time ago someone here did post photos of a hydronically heated [granite?] countertop. It was PEX with a radiant barrier underneath but alas no overhang [or at least none showing].

You might want search here or perhaps someone who has actually done it will reply with their methods and their "ratings" of performance.

In many places in a kitchen though I believe you would want to be quite sparing with counter heat. While it may be good for hot food set out for dinner (particularly buffet-style for a large group) it wouldn't be too nice for cold... You'd probably want to keep it away from the "assembly area" for recipe ingredients as you might start melting butter, wilting leafy vegetables, etc. if they are left out for any length of time. Keep the fruit in a wooden bowl with a relatively tall, slender pedestal

Mark Eatherton1

If it were me...

I'd install small bore tubing in the counter top and power it with a below the sink electric water heater.

This way, you can control the temperature of the countertop and you alleviate the potential light bulb problems with the eclectic grid scenario.

If could be controlled by a simple set point controller with a sensor in the slab. As for the over hang, I 'd think it would work just fine. Don't forget to insulate the bottom side of the counter top unless you really want to see how vegetables (potatos and onions) can grow in the dark...

It wouldn't be cheap to install, but boy, imagine the feeling of a warm to the touch granite counter top in the morning...UMMMMmmmmm... Great way to start the winter day!

ME

Greg Swob

Might help

soften the butter quickly, though! Just reminiscing of all those holiday cookies, cuchen and other treats that valiantly gave their lives in search of my stomach! Greg

JudeNY

Thanks for all your suggestions. I heard that StepWarmFloors may have a recommended undercounter electric mat product but found nothing on their website. I have requested info from them and will post back if I get a reply.

Bob Gagnon plumbing and heating

radiant granite

i use water and the boiler that heats the rest of the house. people love their warm countertops. bob

JudeNY

I got an answer from engineering at StepWarmFloors. He wrote:

"Place 2 strips of heating elements right under the granite. Insulate with polystyrene ( Styrofoam ) under the heating elements. The countertop must rest directly on the heating elements sandwiched between the granite and the Styrofoam. The thickness of the Styrofoam is not so important but there must be no air gap.
The heating elements are 24 Volts and they are powered by a safety transformer. You can hide the transformer in the island cabinet and plug into a receptacle. You may install an on / off ( light ) switch on the primary side of the transformer. For electrical installation follow The Instruction Manual. It is important to note that the two elements bus braids that are close to one another MUST have the same polarity as described in the instructions. Here is a listing of the equipment you need:

12 feet EP-30-2-44W heating element 12" wide.
1 pc EP 250W transformer
1 pc C & T connector kit
1 pc TB 4 x 5 terminal board
1 roll TCu 14-50-B/-W Wire black and white

It takes a long time to heat up a granite countertop and you are better off to leave it on all the cold season. The operating cost is $ 0.25 per day ( American avg.) at max. heating. The expected countertop temperature is approximately 88 F at a room temperature of 68 F but it is also dependant on draft etc. "

Since their product can be run from a regular outlet, I'll have one put in the island cabinet now and it will be there when/if I need it.

Bob, you got me thinking about it when I saw your counter heating a while back in a previous thread. Is there radiant floor heating in that kitchen ?

Someone suggested that since I am heating the floor without setback that the counters will not be as cold as I'm afraid of. Does anyone else think that's true ?

Mike T., Swampeast MO

A few numbers for you...

Radiantly (hydronic floor panel) heated baths with soapstone counters. No setback and truly constant circulation as there is no thermostat/dedicated circulator/automatic valves for the bath floors.

Fully internal bath: Air temp 64.8°; temp of soapstone counter 68.5°. (BTW, average air temp in rooms surrounding this bath: about 60°)

Bath with two south-facing windows (sun hasn't been shining directly on soapstone for a couple of hours now): Air temp 70.0°; temp of soapstone counter 72.9° (BTW, average room air temp around this bath: about 65°)

Note in both rooms that the temp of the counter is a few degrees warmer than the temp of the air--ain't this constant radiant heat interesting?

Subjectively the counters feel on the cool side, but not cold like they [seem] to feel during the summer when the heat is off...

I can't find listings of exact thermal properties for soapstone--only generalities. It is extremely dense, has an exceptional specific heat and "modest" emissivity.

Not certain how it will compare with granite but I think the emissivity of polished granite is going to be close to that of soapstone for some reason...


p.s. If anyone has actual thermal properties of soapstone I'd really appreciate your posting of them.

p.p.s. That five degree above ambient temp of spaces surrounding in these baths is amazingly constant... Still kind of freaks me out how well this works given the experimental nature of the heat transfer system (copper in Thermofin); a mechanical reset of an older cast iron boiler and my "adjusted" heat loss calculation based on output of iron radiators at maintenance...

Bob Gagnon plumbing and heating

countertops

yes, the kit. has radiant floor heating. i simply ran another loop off the manifold for the counters and it's all controlled by 1 wall thermostat. the temp of the counters run about the same as the floor. bob

Phil_6

Now that...

...is slick