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Old 08-20-16, 11:07 AM   #11
CrankyDoug
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Steve;

We live an hour SW of Atlanta so we get weather similar to yours. I planned to put radiant heat in my basement bathroom. The floor has to be cut out anyway because the plumbing is all in the wrong places for the larger bathroom.

The biggest headache so far is trying to find the high density XPS to put under the new concrete. Neither Lowes nor Home Depot have been helpful here. None of the specialty suppliers in Atlanta know what I am talking about which leads me to believe radiant floors aren't common in the south.

I will probably just go back to regular concrete. Twenty years ago things would have been different. I am getting to the age where I don't enjoy home projects and the thought of yet another system to maintain is discouraging.

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Old 08-20-16, 01:40 PM   #12
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Doug, you can also use mineral wool, roxul has a product that will work under slab. http://www.roxul.com/files/RX-NA_EN/...INSULATION.pdf since it is also used for exterior insulation commercially it may be easier to find.

Steve, here is a house built in Asheville, NC similar to how I think you are planning to build. A PhD and an Architect Build a Net-Zero Home | GreenBuildingAdvisor.com In the comments the owners said if they were to do it again they would likely skip the radiant floor.

Like I said earlier as long as there is conditioned air on each side of the floor it will be the same temperature as the air temp. It's not OMG luxurious warm, but it won't be OMG freezing either.
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Old 08-20-16, 02:28 PM   #13
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any insulation is better than no insulation. An inch or 2 of xps above the concrete floor will reduce your heat lag and help the floor feel warmer to bare feet.
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Old 09-14-16, 04:33 PM   #14
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My daughter's father-in-law is a certified residential energy auditor. He is building a new hose in SW MI and wants it to be super tight and efficient ("heat ir with a candle"). After much consideration of alternatives we is going somewhat tradition. Double 4x4 walls. The exterior sheathing is ZIP system, which, once sealed with their tape, provides a very good air/moisture barrier.

The first 2x4 wall is packed with reclaimed polyisocyanurate. It is sealed up against the studs with canned spray foam along with any other cracks. A second 2x4 wall is constructed behind that the traditional kraft faced fiberglass. The blown in fiberglass in the ceiling will be measured in FEET not inches.

(He was going to do SIP, bit the cost of shipping them to his location, the crane and operator and the premium the builder wanted to charge because it would be the first SIP house they ever built, made th cost prohibitive.)
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Old 09-14-16, 04:34 PM   #15
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Quote:
Originally Posted by jeff5may View Post
any insulation is better than no insulation. An inch or 2 of xps above the concrete floor will reduce your heat lag and help the floor feel warmer to bare feet.
Why ABOVE the floor ? Wood flooring ?
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Old 09-14-16, 04:55 PM   #16
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Quote:
Originally Posted by stevehull View Post
Oklahoma is a mixed climate state. Here in central Oklahoma, we have more winter heating degree days than summer cooling degree days. But "winter" is only about 10 weeks long (mid December to March 1). Our first frost date is in mid November and last frost about April 1.
Actually pretty similar to a lot of the mid-west, like SE MI.

Quote:
Originally Posted by stevehull View Post
The use of exterior grade foam insulation, SIPS and tight building techniques (with air to air HRV) are the plan.
Check into reclaimed polyisocyanurate insulation. Big cost saving over new and it has excellent R-value per inch.

Now I am thinking of the in floor radiant cost/benefit ratio . . .

A cheap alternative would be to put in electric resistance cables. It goes against my engineering grain to use high grade power (electricity) just for resistance heating, but maybe that is a better option.[/quote]
No, no, NO ! You will hate yourself when you get your electric bills !

Quote:
Originally Posted by stevehull View Post
Like many of us, my wife and I hate cold floors - so do our dogs. We also dislike carpet and like "clean" floors.[/quote
What does a "clean floor" mean ? Burnished concrete ? Terrazzo ? Bamboo ? Traditional hardwood ?
With any radiant concrete floor you need a vapor barrier and >2" of rigid foam, first.

The first 2 would work well with PEX in the concrete. Terrazzo should be okay but it need a barrier between the concrete and the bamboo (rosin paper) to allow the flooring to expand and contract. Hardwood over concrete is a whole different conversation !

Depending on the number and size of the rooms, IMHO, you want a hybrid system. Mini-split (ductless) heat pumps that also heat the radiant heat water through a heat exchanger. You get the comfort of a heat floor with forced air, as needed, for quicker recovery and high efficiency A/C.

If you have a large number of rooms (3+ bedrooms, living room, family room, dining room, kitchen, 2+ bathrooms, etc) that do not have good "natural" air distribution, the additional air handlers and piping will kill you. At 3000+ sq ft, you will likely need 2 compressors.

Once installed and "tuned" I think you will love it and it would be very cost effective.

Mitsubishi sells system like this but not in the US.
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Old 09-14-16, 08:35 PM   #17
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Quote:
Originally Posted by stevehull View Post
DE
I should have been more specific . . .

The floors are not on grade but above a crawl space so that is not an issue. The floor is not a heated floor but a radiant one with a floor temp of no more than 72-73 F, The home heating will likely be ~ 40% ducted warm air and 60% radiant, so the floors are only about 1/2 of the heat BTU load.

I have been in several passive homes, but have not been in them on a winter morning at 6 AM.

Just materials; PEX, pumps, manifolds, valves, water heater, etc is close to $8K.

This is a lot of $ for a warm floor . . . perhaps a good pair of wool shearing slippers?

Sounds like you are happy with the electric radiant?


Steve
Hi,
It seems like the most expensive and labor intensive part of your floor is the concrete.

We use pex with alum heat dispersion plates air stapled to the subfloor over a conditioned crawl space. Insulation is placed in the joist spaces under the pex tubes. This is cheap and easy and it works -- labor is minimal.
Some pictures here: A Simple DIY Solar Space and Water Heating System

Mostly on this page: $2000 Solar Space + Water Heating -- Radiant Floor Design
The cheap Harbor Freight air stapler made this go very fast.

For us, this is the only form of heat in this part of the house -- whether it would be worth it if you already have a heating system and are adding the floor just to be able to walk on warm floor I'm not sure -- for me walking on warm floors is not really that big a deal, but I know some like it a lot.
I can say that a floor heated to 72F is not going to feel like a toasty warm floor.

Gary
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Old 09-15-16, 05:32 AM   #18
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There are a lot of disadvantages to stapled up hydronic, main ones being required water temp and heating lag. This has been discussed before here. Besides, it's a new build project in a basement.

I imagine the pex and plumbing is going to cost less than heat tape and wires for comparable surface areas, both initially and during operation. Given the short but somewhat harsh heating season, an outdoor reset control would help prevent under and over heating the house, while still maintaining that "warm floor" feeling.
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Old 09-15-16, 06:35 AM   #19
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Let me get this back on track . . .

Oklahoma has a mild winter, with a few windy cloudy cold days. Mostly, it is a sunny winter with days in the 40s and low in the 20s. It is not at all like SE Michigan as I have lived there for seven years (East Lansing) and Michigan has a much colder winter (Lansing, MI ~ 6700 heating degree days). Oklahoma City has 1/2 that or only about 3300 degree days.

The problem is that a "heated" floor, where the floor "feels" heated, requires a floor temperature in the upper 70s to low 80s F. If you do that in a mild winter climate, then you can overheat a well insulated home.

A second issue, with a "heated" floor is the thermal flywheel effect. The home is heated to an air temp of 72 overnight against a temp difference of about 40 F (outside temp in the low 30's). Then day comes and the outside temp goes into the 40s or 50s F with a lot of sun. House heats up as thermal inertia, plus low heating need plus sunshine heats house up to 80 F or so. Too hot.

The above are not conjecture. I have seen several home in the Dallas Ft Worth area (just south of OKC) that have experienced this. Reluctantly, the expensive heated floor system was turned off.

Part of the problems with the homes in the DFW area was that too large a heated mass was used. This was four inches of concrete on top of a crawl space, with 2 inches of foam board below concrete with PEX tubing in the concrete (no ground contact). Despite my recommendations to only use 2 inches of concrete, the builder used four inches. WAY too much thermal mass. Once heated up (they also used high 70's floor temps to "feel" the heat on feet), it took days to cool down. Cooling down the house at mid day meant opening windows in mid winter or running the AC . . . crazy.

Because OKC has a dominant summer, and thus need for air conditioning, there remains the need for that cooling need. Trade offs are present with mini splits vs central ducted heat pump system, but there is still the availability to provide some winter heat with a heat pump with some heat from radiant floor.

So I have decided to potentially use a "moderated" floor where it is perhaps 72-74 F and not in the upper 70s and to potentially use a two inch concrete insulated slab (again above a crawl space or basement). But before this is a well designed envelope with a maximum need for about 36K BTU/hr (3 ton multi stage) heating system. In fact, I already have this 3 ton two stage open loop GTHP system operating.

I am completely remodeling existing house.

The problem is not the engineering of the system, or modulating it so that even and consistent indoor temps are observed - it is the cost! Even with doing all my own labor, it looks like the costs of PEX, manifolds, water pumps, floor thermostats is a couple dollars per sq foot. The cost of a two inch concrete pour is actually small compared to this ($0.70/sq ft for materials).

Bottom line - so it really a good economical situation to do radiant floors throughout a home in the south when you have a short and mild heating system?

Decades of consulting has shown me that well intentioned people will put a perspective WAY ahead of an rational economical solution. I have seen people put in R 100 walls/ceilings (OKC area) because they "think" that this will keep them cool and warm - and yet not pay much attention to air infiltration . . . .

I have appreciated the many posts, but the issue seems to be economics - and the wife. She hates cold floors and she hates wall to wall carpeting (as do I). So it will be a lot of bare clean flooring, but perhaps electric radiant heating in just the bathroom will keep her happy. In there, I can heat that small floor area to 85 F!


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Old 09-15-16, 08:00 AM   #20
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Quote:
Originally Posted by stevehull View Post
Oklahoma has a mild winter, with a few windy cloudy cold days. Mostly, it is a sunny winter with days in the 40s and low in the 20s. It is not at all like SE Michigan as I have lived there for seven years (East Lansing) and Michigan has a much colder winter (Lansing, MI ~ 6700 heating degree days). Oklahoma City has 1/2 that or only about 3300 degree days.
Nice to see that you have data !

Quote:
Originally Posted by stevehull View Post
The problem is that a "heated" floor, where the floor "feels" heated, requires a floor temperature in the upper 70s to low 80s F. If you do that in a mild winter climate, then you can overheat a well insulated home.

A second issue, with a "heated" floor is the thermal flywheel effect.
I have limited experience living with radiant in floor heating (a relative had it). I don't understand your first statement. It seems illogical as a stand alone statement.

#2 is something I never considered ! Even with a wood floor (over a condition crawl space) and forced air we can experience the "flywheel effect", too a much lesser extent, in SE MI !

But you have the solution. Limit the mass that is heated by the radiant system. Make the flywheel smaller ! Possibly, tubing connected to a wood sub-floor.

I still think a "hybrid" system (where the radiant heat water is heated by a heat pump) IS a good solution !

Quote:
Originally Posted by stevehull View Post
Bottom line - so it really a good economical situation to do radiant floors throughout a home in the south when you have a short and mild heating system?
I think you are asking the question incorrectly ! The real question is, "Is my family's additional comfort from radiant flooring worth the $XXXX ?"

Quote:
Originally Posted by stevehull View Post
I have appreciated the many posts, but the issue seems to be economics - and the wife. She hates cold floors and she hates wall to wall carpeting (as do I).
"HAPPY WIFE, HAPPY LIFE !"

Quote:
Originally Posted by stevehull View Post
So it will be a lot of bare clean flooring, but perhaps electric radiant heating in just the bathroom will keep her happy. In there, I can heat that small floor area to 85 F !
The question I have about electric resistance heated floor is recovery time.

If you let the floor "coast" to a lower ambient temperature over night. How long does it take for it to achieve your desired temperature for your morning shower ? This can be mitigated by a set back thermostat.

But, can you live with that cold floor for that middle of the night trip to the bathroom ? How about a cold floor in the middle of the day ?

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