Hello…I am grateful to be able to turn to this expert community when I need coastal building information.
My quandary is this: We are building a small home on the Oregon Coast. Because of Planning Office restrictions, we must build right on a concrete slab. For a lot of reasons, we have chosen porcelin tile for the main floor, with woollen area rugs.
I want a warm tile floor, but I want to be as energy efficient as possible.
I can’t find any information comparing whether PEX tubing IN the slab or the warming mesh in the thinset are more conserving of energy in the long run. We do have a natural gas source for a hydronic boiler if that’s the smartest way to go. The main floor will cover only 912 sf.
I’m not sure what the pros and cons are of each method otherwise, as well.
I am hoping someone here will be able to give us some good, sound advice on this.
Thank you!
Edited 6/29/2007 6:35 pm ET by Curious_Green
Edited 6/29/2007 6:35 pm ET by Curious_Green
Replies
In terms of energy they use exactly the same amount.
But you need to look at YOUR cost for that energy. For the electric for the mat or the gas (and include the boiler loses) for hot water.
But, in general the electric mats are only designed for supliment heating. You need to check the watts/sq ft.
To save energy you need to properly detail the under slab and edge insulation.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
"In terms of energy they use exactly the same amount."
That depends. If you are only counting energy used at the house, the electric mat is more "efficient", since it is virtually 100% efficient, with all the energy used being converted to heat delivered to the home. Hydronic heat is only as efficient as the boiler, usually around 90+% for new units. The rest is lost up the stack.
If you are counting total efficiency, including the efficiency of the elec utility's generation plant, that depends as well. If it's hydro or renewable, like wind, you are probably still ahead of the game with elec heat. If it's coal or gas, I'd be surprised if a new high efficiency boiler isn't better than the gen plant + transmission loss. If it's nuclear, well, how do you define "efficiency"?
If you are measuring "efficiency" by cost in dollars, that depends on your rates. But, the bottom line is, if you are really concerned about conserving energy, the place focus most of your efforts is in properly constructing the building, not picking a heat source. I get a kick out of folks who think they are "conserving" just because they have a high efficiency furnace, while at the same time having 3 acres of glass on a north-facing wall, 4" of insulation in the ceiling, etc.
Mike HennessyPittsburgh, PA
This brings me to another area which I've been pondering: Because our piece of the Oregon Coast has a yearly average of 80% overcast skies, I don't think installing solar panels would be worth it.However, our "small and tall" house (thanks to Lincoln County Planning Office) will have a max elevation of 30'. The building code wind load is 110 mph.How do you think a windmill generator would work on the top of this structure? We are about 4 blocks from the ocean, but the prevailing winds seem to be more from the south than the west, toward which we have an open access.Again, I am so appreciative of all of your responses. I am learning a great deal of essential information.
I'd stay away from a windmill on the roof due to vibration noise but you may want to take a look at evacuated tube collectors. They are amazingly effective on cloudy days as compared with flat plate collectors.
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"You cannot work hard enough to make up for a sloppy estimate."
I'm also on the Oregon Coast (which is irrelevent to your question), but as someone else mentioned, the answer probably has to do with whether you're hoping to heat the room, or just the tile floor.
If it's the tile floor, the heat mats are great. I've installed several of them and by far the best as far as I'm concerned is the Warmly Yours system (dorky name but good product). And they have customer support people who are as good as any I've worked with for any product.
(In Eugene, OR)
I have experience with Watts Radiant products--Suntouch mat and Warmwire--over slabs.
If you're not familiar, suntouch is the prolific orange mat you see a lot, it's cousin is the wire with out the mat, warmwire, that installs as you choose to space it between tracks glued to the slab or whatever.
Both products run on 120 or 220, larger installations should run on their own circuit and both are easily controlled with a 140$ programmable thermo that's easy to use and works great.
Over the slab specifically, I would rec. the warmwire. This allows closer spacing, down to 1.5" (where suntouch is spaced out wider already in its mat), that can concentrate the heat more. It is rec. in the literature to install a barrier of cork or otherwise that can keep the heat moving up rather than into the slab. I could not find such a product here and locals with experience in the product said they put it over slabs all the time and never use the cork mat.
I put Warmwire down over a slab, spaced at 2" in a dark basement--warm floor my rec to the HO--and it went great. It can raise the floor temp up to 20 degrees warmer--75 or 80 in the dead of winter. Takes a bit longer with the slab tho to heat up.
On the other hand, I put a 20sqft suntouch mat in a bathroom, under slate tile over slab, and it is not nearly as effective--maybe raises the floor temp 10-12 degrees at best and over a long time...
In my own house, i put 200sq ft of warm wire under slate floor in my kitchen--backerboard over ply subfloor--insulated--open crawlspace and on the program we have it "wake up" to 80 degrees in the am, then sleep, then wake up to 80 when we get home. Constant during the day on the weekend... It is enough to heat the whole room. I could run the floor up to 90 or more without pushing it I think... If we run this program constantly, each month the utility bill is 20$ more than usual. Product literature will show in charts how much wattage is produced and how many amps can be pulled by each mat/wire size.
Watts radiant product info--installation DVDs and customer service are excellent in my opinion.
I would not rec. suntouch mat over the slab--only the warmwire system. BTW Warm wire is less expensive the more sq ft you get, compared to Suntouch mat which can really cost!
Another rec. if you go this way. Buy the 30$ beeper that will sound during installation if at any time current is interrupted or a wire is damaged by trowels/tiles/or whatever. I saw an installation where 2 entire quadrants of the mat did not function. About 1500$ of material for a large cold rectangle in the floor. The beeper is good insurance!
Hope this is of help!
Pat
A warming mat only warms the floor and wil not heat the house.
But a properly designed radiant hydronic floor heating system is the most efficient, comfortable heat I know of.
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Energy efficient. To get this, insulation is the thing to get right. Heated floors are the nicest heating system there is. electric or hot water.
Insulate the slab as much as you can. If not you end up heating the dirt underneath.
Heat takes the easiest route including down.
You can use electric mats to heat the whole house. This is common in Europe. But you must cover the whole floor for best results.
With all electric there is very little maintainence. Control gear fits in a wall box.
With a "boiler" yearly servicing wil be needed and depending on the type of boiler an air supply and exhaust. Hot water system also require a pumping system and somewhere to locate the boiler and equipment.
The right insulation will give you the best value with either system.
All of the replies I received are welcome and valuable!
This is a great resource...
Thank you.
Insulation is vital. Generally 2" of rigid foam under the slab, with something around the perimeter as a thermal break.
As for electric under the tile or water in the slab, I think you'll have trouble getting enough heat per square foot out of electric. However, a qualified HVAC person can do all the calculations for you -- installation cost, operating cost, and capacity. There isn't any reason to guess when the calculations can be quite accurate.
Curious Green,
Bottom line think about the future. If the cost today of natural gas is X and the cost in the next decade is going to be 2or 3X you need to consider seriously what you best deal is..
Payback is a word that is bandied about a lot. To figure it out you must envision the future..
How difficult will it be to make electricity? compared to how difficult will it be to purchase natural gas?
Solar power, wind generators, mini hydro, etc. all stand a chance depending on factors..If you control the means of production you control your costs to a degree that those who must buy their energy don't..
Frankly it's far more cost efficent to make a payment at a fixed cost for future power needs even if today it's cheaper to purchase than to produce..