Slate floor vs porcelin tile fllor.

actually, although it's a 1950's cape, we completely remodeled it when we put in the radiant heat. all insulation has been updated to current standards or higher. i do wonder about the application of the radiant and insulation below it in the joist bays. we have track radiant in one area with 8" of fibreglas below and underfloor clip on in another with radiant barrier stapled across joist bays. neither seems to be very efficient.

 

The only way to gauge the efficiency of any heating system is to calculate the net BTUs used for any given temperature average in the building. For example, a small BTU input over a longer period of time may be more efficient that a larger input over a shorter time.

One must realize that with hot water radiant heat, the burner may not be burning all the time, or not burning at full capacity. A hot water circ system will maintain significant heat even without additional input. It is most efficient when the delta T between the input and out put is as close as possible. That is why radiant heat takes a long time to get warm, but stays warm (comparitively) longer.

Icarus

 

exactly.

 

Radiant is also likely to be more efficient A:because true zone heating is possible if properly designed (shutting off air to a room in a forced air system forces the furnace to work harder, and blow extra air into the open vents creating drafts) and B: with radiant, there are few if any drafts, making it feel cooler than it actually is, C: because the temperature of the circulating water is closer to that of the ambient temp, it is less likely to have over heated air rising (due to forced air) and having a greater Delta T at the ceiling level. Total heat loss is very much a function of the Delta between the hot side and the cold side. The greater the Delta, the more BTUs per meter ^.

I have never done a calc to prove the above but it seems to be intuitively true. (that's my story and I'm stickin' to it.)

Icarus

 

op2:

 

One small thing about slate: My mom's foyer and receiving room have slate flooring, these big rough hewn slabs that have been polished. When I was growing up, I was always reminded to avoid using that entrance out of concern for the floors. To this day, I tippy toe through, or avoid the area entirely.

Slate's fairly soft, isn't it, for normal use? I suppose it'd be okay if the distressed look were acceptable, otherwise, I don't think it wears so well. And it seems really cold, I wouldn't want to stand on it for long periods of time, as one would in a kitchen.

 

Tile on cement will be cold, too.

Slate's hardness varies, and the range is likely greater than other stones. Slate roofs have lifespan ranges from 50yrs. up to 400yrs. depending on the hardness of the stone. Slate floors generally aren't recommended for high traffic areas though. Our 100yr old house still had a slate floor in the back area of the basement. I pulled some up to use for a garden path. After all the time laying on damp sand, several layers of stone were left behind, some more just washed off, and the @20 by 40 inch slabs easily broke up into pieces for the path. The bottoms are still disintegrating to a degree outside.

I vote for tile simply because it will be easier to clean, and have dogs also. Be careful though, it can be quite slippery when wet.

 

You know, that's true come to think of it, my parents owned a slate roofed home in PA, they say they last forever.

 

This may or may not interest you, we have many large dogs and they have the run of the kitchen dining room area when in the house, the yard they hang out in tends to be a mud pit in the spring and fall, as the ground freezes and thaws and there was-is always a bit of a mud problem, finally we ordered 10yds of 1 1/2" washed gravel and spread it out about 2-4" thick in the heavy traffic area of the dogs outdoor yard, no more mud in the house, works great, doesn't look bad (it's a dog yard...)
Boy, radiant heat in the floor, those dogs are going to love you.

 

Frankly, 'current standards' are woefully inadequate in my opinion. They are based on fuel prices in the eighties. Anyone still paying what they did in the eighties? That said, if you are needing to start heating your slab at 4am to get it to 58F, it seems unlikely to me that you are getting the benefit of even that amount of insulation. Can I recommend that you get a competent energy audit?

Efficiency is input BTUs for a given temperature difference between inside and outside. It will probably need to be averaged over a significant period to be useful.

The thermal mass of the water is generally a loss as most of that water sits in unoccupied spaces. The reason that radiant heat takes a long time is generally the thermal mass which is in the occupied spaces of the house (e.g. slate floors). Additionally, old boilers generally are more efficient burning hot and then shutting off. Modern boilers thus tend to have very little liquid in them (a few gallons), and are designed to modulate (burn well at lower than full blast) and at lower temperatures, as all those things improve efficiency.

Absolutely. In order for a porcelian tile floor to be as warm to bare feet with in floor heat, as a wood floor is without it (i.e. at 68F), it would need to 83.2F. For a slate floor that number is 85.0F. And wood floors at 68F aren't particularly cozy; so it will need to be even warmer, to be cozy.

 

I've installed slate so far in 2 rooms in various houses, and am working on a third.

It is a soft stone, but a nice stone. I would never install slate-looking porcelain. If you want a porcelain then get something else. But imitation slate is no imitation. It is by far the most horrible installation process you will ever face for tile if doing it yourself. But the end result is worth it.

As mentioned above, the tiles are not square, the tiles are not all the same size, they are not all the same thickness, some will have quarry marks on them, some will be broken in the box, and then the fun bit: all the texture on top. That texture makes it nearly impossible when grouting, but is the part I love the most. I found it best to use a good quality sealer (or enhancer then sealer) before grouting. Then grout and immediately wipe away. Don't let it haze or anything like with porcelain/ceramic. All those nooks and crannies is another place for grout to hide. After grouting, then seal again including all the grout lines.

I also recommend putting a layer of Ditra down below the slate. It will separate it from the floor below preventing cracking to a degree. I have electric heat under both tile installations and it feels really good on the feet. For a main traffic area though, water radiant would be better and more efficient.

 

There is no substitute for real slate. Like above, it is a nightmare to install but it also has its advantages:

Its randomness makes laying it somewhat easier...you know it won't be straight, you know it won't be level so the amount of prep is a bit less.

Here is my theater room that we recently finished: