Radiant Heat- Monthly operating costs

[Jagman]

I am seriously considering installing radiant heat (gas) in the concrete floor of a newly planned garage 32 x23 with a 10 foot ceiling. I plan on fully insulating the 2x6 walls, ceiling and 2 garage doors. I live in upstate New York where it is in the low teens at night and upper 20's on a typical winter day.

I will be using the garage a couple of evenings during the week and on weekends. I am aware that radiant heat must be left on all the time as it is slow to warm up. Given this, can those of you who live in similar winter environs give me a sense of what it costs a month to operate such a system and how warm you keep the temperature?

Best,
John D.

 

[koditten]

Jon:

Check back with me on the 22nd of January. I'm watching mine like a hawk. All I know so far is that I used 16 bucks more in natural gas than I did last December. I started my system in the middle of a billing cycle.

 

[hdemk1]

Jon, your garage is roughly 100sqft bigger than mine, which is 930sqft. Mine has 9ft ceiling, sadly couldn't go any higher as there is two more floors on top af that. What I'm saying is that they are somewhat comparable in size.

Constuction material differs quite much. Our whole house is built from concrete. Walls are 15 3/4" thick, there is 5" PS foam insulation in between the concrete cores. Check this one out and you'll get the idea of the material. It's a very, very good insulation to protect from our cold winters. It is massive material (only our house's concrete material weights 530 thousand pounds itself...) which stores the heat and evens temperature variations very well. I don't recall seeing any of this kind of building material available when I lived in Maine for a short while in 2001-2003. Well, that was minimal intorduction to the subject of how to build a house in Finland.

Let's get back to your original question. We heat the whole house, all three 3 floors, with radiant heat in the floors. Very common way here in Finland. We have a heat exchanger/compressor. It is taking the heat from a deep well. Diameter of the well is 6,5" and it is in our case 690ft deep. It was drilled to bed rock, it is full of groundwater and there is constant temperature from 39 to 43 Fahrenheit. That is enough for the pump. The compressor takes 4,6kW/h and the output efficiency is 15kW.

My garage floor takes roughly one third of the produced heat, maybe a little less. The same compressor unit is also heating our hot water, there is integrated 140 gallon tank for that purpose which is more than enough. We need electricity to run the compressor but compared to the total square footage and volume of our house our yearly consumption of electricity for heating and hot water is very close to 9 250 kWh. I estimated that the garage floor takes roughly 1/3rd of the whole heating consumption, let's say 3 000 kWh. With our electricity expences, it equals to ca. 380US$ per year, monthly cost being 32US$. I don't think that is too much to heat a garage, no matter how much you use it.

I like the radiant heating method, it is very nice to work on warm floors. It is even heat accross the space, it leaves all walls open for any kind of set up of your cabinets, tools etc. More people should go with it. It might be a bit more expensive to invest in the first place but it pays back with many ways, I bet moneywise also in the long run.

I'm interested to hear how your consumption figures evolve. Don't be too shy with the insulation though. Roof insulation is very important as you must know. Minimum in Finland is 20" nowadays, that's how much we have. Works fine.

I can post some pics later if you are interested.

 

[Jagman]

Your response is very helpful. I now plan to add extra insulation in the attic area. I won't get this project going until summer but will be sure to post some pictures.

Best,
John

 

[arb905]

make sure you insulate under the concrete before you pour, tell the contractor your plan. A good radiant barrier and some foam will help to radiate the heat into the space instead of losing it to the ground underneath. Are you going to use a boiler or electric?

 

[svtride]

My shop is in SE Michigan. Your temps sound similar to my location. Shop size is 25 x 50ft. Fully insulated 2x6 12ft. walls, blown in attic insulation and 2 or 3 inch closed cell foam core insulation under the slab. Heat with natural gas high efficiency water heater. Shop temp kept at 60 degrees F. Roughly $90-100/month to heat. Gas prices are lower this year.

 

[hdemk1]

make sure you insulate under the concrete before you pour

Very good comment indeed. That's what we did to the living floors and garage floor too. Living floors have "only" 1 1/5"-1 4/5" insulation (heat coming from bottom of the floors too because of heated space below), but if I remember correctly the garage floor has 5-6" insulation underneath the pour. This went up to 8" last year I guess.

We wanted to control the radiant heat direction with the insulation and leaving the PEX-piping very close to the surface helps to even the temperature variations outside. It reacts very well and the inside Dt is very small.

There's a clear trend here in Finland to make houses so well insulated that the energy to heat the house is minimal. After 40years or so we will get to see the possible problems of that decision...

Because we had to dig to get to the correct level there was no way how we could have had ventilated foundation bed. So our foundation bed under the pour is crushded gravel to take the load (of the house) and then broken stone to prevent capillary humidity problems. On top of the broken stone sits the insulation. Insulation is the key. No matter how much you heat if insulation *****, the heat doesn't stay in the space.

 

[Jagman]

I plan on using gas. My floor size will be 24x32 with 11 foot ceilings. All else being equal, it looks like my monthly cost should be in the neighborhood of $60.