Indoor air temps with radiant floor heat

[donjuedo]

I have seen many posts mentioning radiant floor heat in different contexts, but I have a specific question that (I think) hasn't been addressed.

In a regular home, it's understood that turning down the thermostat in Winter saves money. The cost of heating is less because the temperature difference between indoor air and outdoor air is less, so there is less heat flow outward.

In a home with radiant heat flooring, not just in the basement, floors are warm, so air has to be cooler, or we'd overheat. With cooler air, the temperature difference between inside and outside would be less, so there's less heat loss, with no loss of comfort.

Now, what I'm wondering is, in the experience of folks who have lived in such a home for a winter or two, how much less is the air temp? It might be that people no longer measure it or look, since it's not really the heat control anymore.


Peter

[rreidnauer]

Are you sure about the observations you stated?

[donjuedo]

Are you sure about the observations you stated?

I had not doubted any until you asked. I've been reading about radiant heat flooring for so long, I can't separate what I have read from what I may have assumed, or even misunderstood.

[thoner7]

Per Timbrewolf "With the Geothermal system producing 115 deg water, I can set the basement thermostat to 55 deg (slab temp is 65 deg) and it FEELS warmer than the 74 I have to set the crappy forced air system in the rental house at just to be comfortable. This alone, keeps the upstairs above freezing, in -25C/-13F outside temps, in a house that is not completely sealed/caulked and only has the outside chinking installed."
http://community.loghomebuilders.org/showthread.php?12245-Preventing-Water-and-Thermal-Break&p=111877&viewfull=1#post111877

[donjuedo]

Yeah, I saw that. The first line says "the basement at least". So I added, "not just in the basement" to my post. I'm planning for more than the basement, and want to compare apples to apples, as best I can. In fact, it was Timberwolf's post that got me to wondering.

[Timberwolf]

Had it in the previous house too (basement and main floor) even though it was a poorly designed system, it was the best heat EVAR (ok, second only to sitting next to a roaring fire on a cold winters day, but i digress). No doubt some of it is physcological, but i have couple of trains of thought on it (note, my mind is a trainwreck, viewer descretion advised).

Moving air (forced air) feels cooler (why we run a fan in the summer). In floor heating warms your feet and if your feet are warm, the rest of us usually feels warm (think of heat flowing up through the body and out the head).

In floor radiant heat saturates the floor and the building and all the objects in the room. Forced air ends up at the ceiling (which in my place is 21 feet above the top of my head).

Flywheel effect, like the thermal mass in a log home's walls, the slab/fllor stays warm for a long time.

My wife's statement: I was never cold in that house (the one with the radiant floor system). Note: she was cold in every house before and since.

I can tell you it feels better, in that old house the kids would lay on the basement slab with a thin area rug and watch TV in the dead of winter. Bathroom and kitchen tiles that are warm to the toes. Try that with forced air.

[rreidnauer]

I don't doubt radiant being superior to forced air.

Question fuzzy. At the old house with radiant, did you also have the thermostats set at 55F? If so, then it would pretty much confirm the answer to Peters question, that there'd be about a 15~20F difference in settings between the systems.

And the flywheel effect. I see that even with the woodstove in the camper. When it's cold in the trailer, (like when coming home from work each evening, and the propane heat has it at 50~55F) it takes a while (and a good chunk of wood) to not just warm the air, but everything inside. Once at temperature though, it is easier to hold it there, even if I get a little behind on reloading the stove.

[Timberwolf]

The basement was set similarly low, the upstairs lower than I would have in the current rental, but not as low as 55. But I attribute that to poor installation and poor construction of the house (crappy stickframe and a staple up pex install with no insulation) more than anything.

If I ever do another (chances are i will) I would definately tweak a few more things to get more effiency and comfort.

[thoner7]

Timberwold - you run your hot water with a Geothermal system right? How do you like that?

Im trying to decide on the best way to heat that water. A new EPA approved wood boiler is 8k or more. A high end natural gas boiler is about the same and crappy quality. I've heard of others using a hot water tank but I'm not sure if it could handle the load.

[Timberwolf]

The unit/install looks amazing, but since i have no idea on the (real) operating costs yet I can't comment. Mine is a triple function unit; heats water (115C), air and chills for AC. Surplus water from the desuperheater function goes to a second water tank as a preheat for domestic, so cost ofsets are in place.

Was hella expensive, and probably 1000% overkill for this house.

Learning experience (expensive).

Next time, much less.

I've seen the water tank setup. Not ideal. Your first investment should be insulation, then it takes less to run. The new wood boilers, I dismissed for multiple reasons (indoor or outdoor?) $8K would be a steal up here. I've seen $2000 propane boilers that would fill the bill, not sure about long term costs.

Wood and geothermal: Wood you have to be home to load, and electricity (where i live) is the most expensive in North America and often goes out for days at a time.

Planning, lots of planning.

That was random and disjointed. Need more sleep and coffee.

[rocklock]

I have a timber frame home (rental) next door with a ICF basement and radiant heating in the basement floor (only).

It takes about 24 hours or more to get this sucker warm (we have loaned electric heaters to some guests). The basement and first floor are very comfortable. The thermostat is on the first floor... The basement floor is warm (toasty). This home is the reason that I put in radiant heat although is is not active yet. No problems on the second floor...

Note, I have no temps... just observations. The house has been there and operational for about 10 years...

[loghousenut]

I can't add much to the theoretical discussion about the relationship between floor temps and air temps. I do think the principles become apparent when you drive a car with heated seats. Sure solves a lot of arguments about who controls the heater knobs.

[panderson03]

this is a very helpful thread! great tip about insulation around RPSL footings!!
and I agree with Mr Nut. seat heaters save marriages....