Radiant Flooring in Oklahoma
 

I am designing a new home and have been seriously thinking of radiant flooring. This would be the PEX in concrete, insulated from below, etc. I would do it myself with a helper (~ 3000 sq ft).

But the price is steep - even if I do it myself. I already heat and cool with geothermal heat pumps (ducted air).

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.

Most winter days are above freezing, are sunny and it really isn't bad (compared to where I grew up). A typical winter night is in the low 20s (F) with daytime temps in the mid 40's or so. Then there are those nights that drop to zero F, a terrible north wind and a high the next day a high temperature barely in the teens . . . . .

The use of exterior grade foam insulation, SIPS and tight building techniques (with air to air HRV) are the plan.

Now I am thinking of the in floor radiant cost/benefit ratio . . . I would love to hear from others in the so called "south" that have or have not put in radiant flooring.

I grew up in New England and there is no question of how good it would be to have there - but in central Oklahoma - and for the relatively short winter?

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.

Like many of us, my wife and I hate cold floors - so do our dogs. We also dislike carpet and like "clean" floors.

Appreciate your thoughts and time in advance.


Steve

What do you mean by cold floors? If cold floors to you are in the mid 70's then you may need some form of radiant heat in them. If however you can tolerate a cool floor then you likely won't find a benefit to heating the floors.

I take it this will be slab on grade. The most important thing you can do is insulate the slab and foundation. This alone will warm the floors up considerably.

How close are you to construction? You might try hunting up a local passive house and try their floors out.

We put in radiant floors in our crawlspace built house. Yes the warm floors were nice, but we no longer run the system, for a few reasons. #1 it was expensive, without a natural gas line we had to buy propane, the rental charge on the tank was a bit crazy, as was the cost of the propane (this was back before fracking took off and the cost of propane was rising with shortages happening in some regions). #2 it was a bit unreliable. all of our pumps failed (this was due to a commissioning and design issue), the water heater died (high efficiency condensing water heater), and we battled leaks. #3 it had comfort issues, the stairwell became much warmer than the rest of the house. In the end it was the cost and leaks that actually stopped us using it though. After the replacement water heater died, we disconnected the system entirely and put in an electric water heater. Later when we redid the master bath we put in electric in-floor radiant heat there.

Ironically there have been a couple of times where I was glad we didn't have in floor heat. These are when I have been really sick. When I was really nauseous a nice cold floor to lie on (in the bathroom with my head in the shower) was really nice.

Done well radiant in-floor heat is very nice. To do it well you absolutely need to have a professional familiar with your construction techniques, and climate design the system. In a well designed and built house the only major comfort factor they improve is warmer feet. In a highly energy efficient house however the floors may never actually get to toasty feet levels of warmth.

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

If your floor temp is only going to be 72-73 with a air temp around there I would skip the radiant flooring. Especially if it is not slab on grade. Insulate, seal, and condition the crawlspace, and the floor will be the same temp as the indoor air.

As for the electric floor... not really. Again it's an install error. Where it works it is wonderful, but it has never fully worked correctly. The sub tile electric matts need a good installer who has worked with them before.

I know you are a big geothermal buff, but you might look at other equipment and use the savings for radiant flooring. I'm especially smitten with the warmboard system (I tried to convince my dad to use it on this house, but he refused).

My suggestion: If you are considering spending $XXXX for geothermal / radiant / solar / whatever, do a heat loss calculation assuming you spent the same $XXXX for upgraded windows and insulation. Then think about the increased comfort of the superinsulated house, better ability to ride through power or furnace outages, ....

Our house recently went through a two day power outage where the outside temperature hit 90 degrees F. The house stayed a steady 75-77 degrees inside.

JR - I already have a geothermal heat pump and I am talking about building with SIPS. I have done other homes/building with SIPS and am comfortable with them. Am recycling the thermal double pane Pella windows as well as air to air heat exchanger, etc.

The specific issue for radiant flooring is the cost vs. benefit for my location in Oklahoma considering the relatively short winter.

I grew up in New England, did grad school/post docs at Michigan State so I certainly know about really cold winters (as you do).

Will do the radiant myself, so labor is not the cost issue.

One major issue is overheating as thermal floors have a long lag time and we often have winter bursts that are frigid, but a few days later, the temps are in the 40s. A recipe for overheating.

I have done the manual J modelling with a 60% contribution from the geo air unit and 40% from radiant. The flooring is not a hot floor - but a conditioned floor, about 72 or so F. Set air temp at a couple degrees lower.

For that reason, the floor concrete surrounding the PEX tubing will not be 4 inches thick, but perhaps only two inches.

I will likely use a water to water geothermal heat pump to provide hot water for the floors and I already have a drain back hot water solar system. Then I also have the desuperheater from the water to air geo unit. I have LOTS of hot water in the summer.

Anyone down south use radiant flooring? Or maybe I should just go with electric radiant - even thought I hate the idea of using 60 Hz electrons for resistance heating . . . .

Electric radiant is cheap to install, but pricey to run.

You don't need to ask why we need a ducted air system - been close to 100 F for the last couple of weeks. Forced air A/C is not a luxury down here - it is a necessity.

But we have a LOT more cold weather also - temps down to zero F. That is a lot of heating degree days (60-70 each days when it is that cold), compared to the need for a daily cooling degree day on a hot day of about 1/2 that. So we have a dominant heating need.


Steve

Have you looked at tying the radiant to your drainback like the systems at build it solar?
They put the pex just under the finish flooring, and it may be less prone to overheating and more responsive to changes. Also solves the cost issue since the hot water is free...

ksstat,

Yes, I will incorporate solar water heating for both domestic use and for radiant. I will also tie in the existing water to air GTHP desuperheater into this. A separate water to water GTHP (to be installed), existing hot water solar panels and existing water to air GTHP will all supply a separate 50 gallon (200 L) preheat water tank. In the summer, my existing three solar drain back panels (total ~100 sq ft; ~ 3 sq meters) provides FAR more hot water than I can use for domestic use (dishwasher, showers, sinks, etc).

All this can be done. I am already preheating my domestic water with the drain back panels and the water to air GTHP desuperheater. The problem is winter when it gets VERY cold. Oklahoma is not in the deep south of the USA, but in the middle area where we get little winter sunshine (drain back solar panels don't provide much hot water) and the desuperheater on the water to air GTHP also does little. I will have to employ another way to heat the water for the PEX radiant system. By far, the cheapest way to do this is with a water to water GTHP as it has a COP of ~ 4. But it is also very expensive to put in.

In the winter, the majority of the radiant water (90%?) will have to come from a source other than my solar drain back panels and the desuperheater GTHP. The cheapest installation is to use a 10 kW tankless water heater, but it is by FAR the highest in yearly operating costs. Next is propane, but it is almost as expensive as electricity.

So, my real question, "is it all worth it"? I can do it, but the cost to do so is expensive with such a short winter.

An alternative is to put down radiant electric resistant mats in the concrete (insulated below) in bathrooms and areas where my wife complains about "cold" floors. Cheap to install, expensive to operate . . . Mind, you, the floors are not cold, but probably about 18C (65F), but because we don't have rugs (allergy issues), the foot "feels" cold due to conduction.

Wife was in a home (in cold Michigan) a few winters ago, where they had radiant floors and she fell in love with them.

The issue may all be settled - happy wife, happy life; I may just end up putting in a very expensive system for a 10 week winter . . . . .


Steve

I have discussed radiant flooring with several contractors in your area.
All use 100% water.
All start from one central place and stretch the tubing to each room so all the tubing are exactly the same length and therefore the same pressure. Most build with stemwalls which are back filled with sand. That's were the tubing is placed as opposed in the slab.
Some of the local concrete companies offer a mix that's made to imbed per in the slab. Swartz comes to mind.
Some of my neighbors have had radiant floors for ten years. The ones with the pex on one foot centers have warm and cold spots while the ones with 6 inch spacing love it. They consider radiant heat to be the base heat. They still use other forms of heat to supplement that. 100% of the folks I've spoken to use hot water tanks as their radiant heat source.

Philb

I appreciate the local perspective as you are quite close to me. I agree on the spacing as well (6 inch).

Thanks for the confirmations!

Steve

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.

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.

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.

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.)

Why ABOVE the floor ? Wood flooring ?

Actually pretty similar to a lot of the mid-west, like SE MI.

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 !

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.

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

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.

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!


Steve

Nice to see that you have data !

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 !

I think you are asking the question incorrectly ! The real question is, "Is my family's additional comfort from radiant flooring worth the $XXXX ?"

"HAPPY WIFE, HAPPY LIFE !"

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 ?

Wizard,

Here is the logical behind my apparent illogical statement . . .

For a floor to feel like it is "heated", the floor must be about 80 F at a minimum. This temperature cancels out the conductive cold perception of a bare, no carpet floor (such as concrete, or ceramic tile/plank).

Conduction plays a large role in cool/warmth perception. For example, if you put your hand on a steel plate that is 85 F, the steel plate will "feel" cold. Your hand on a similar temp piece of wood will not "feel" cold. Same temperature - different perception of temperatures.

If we do this thermal floor, we will embed PEX pipe in two inches of concrete (on top of foam boards) and then put down a hard flooring material over that (ceramic planks or laminate). Ceramic has a lot of conduction, so even an 80 F floor will feel "coolish" to bare feet - but FAR better than a 65 F floor!

Laminate is not as great a heat conductor as ceramic (or concrete) so it "feels" a bit warmer, but not as warm as a true wood floor. I have had wood floors in the past and I am so tired of getting them refurnished every couple years. We have big dogs and, in spite of multiple coats of hard polyurethane, you can still soon see the wear marks in the pattern of where the dogs come in and out. The last flooring company "guaranteed" their finish for ten years - it lasted three. Turns out, they guarantee the material, not the labor. Tired of all the dust the sanding causes.

Make no mistake, a wood floor is beautiful. Just tired of the upkeep.

Does my logic on "warmth" reveal itself now?

Steve

I work in commercial HVAC. We had a job were the engineer spec's the in floor heat built with 6 inches of sand between the insulation and concrete. So it was 2 inch foam, re-mesh, pex, 6 inches of sand, 4 inches of concrete.

Because sand is a poor conductor of heat, the heat from the pex rose through the sand and little was conducted down to the insulation.

I like that design.

OK, so with a fairly even split between forced air and radiant in heating mode, you should be able to use the waste water from an air handler coil to heat your bathroom floors. This would alleviate a lot of the design concerns you have. Regardless, with a smaller than usual heat load, you won't need a huge slab to hold the BTUS.

Steve - I think the dogs will scratch up the laminate also. It might take them longer, but ...

You sound like a well informed individual, so I guess I really can not question your 80+F statement for a "warm floor", but that still sounds quite high.

If you don't want the thermal mass, why are you putting in concrete ? I assume you are going to use a light weight, self leveling type of concrete. With that type of product, you only need it thick enough to cover the PEX so it would be closer to 1".

If this is on top of a wood framed subfloor, you should double check the framing underneath and check the subfloor for level. The self-leveling stuff really works, but if you have low spots it will be very thick and will take longer to cure. High spot are worse, because more product has to be add to the whole area.

all right steve, lets take this from another angle. What is your energy budget? Do you want to eventually go net-zero? It seems to me that is going to be the decision point. If net zero is more important to you than warm floors, then the warm floors are probably a waste of money. same with going extreme energy efficiency...

That said you don't have to go gonzo with insulation and if you have clerestory windows you can use those to control some extra stack driven exfiltration to deal with overheating issues from a well air sealed house. you are just going to pay an energy penalty for that.

It is claimed that "Luxury" vinyl is pet friendly. It has low conductivity compared with other hard surfaces, so it might feel a little less cold if you decide to go without sub-floor heat. Still cold compared to carpet though.

Do you clip your dogs' nails? That might solve one of your problems. We never did but the wear of one dog was negligible by comparison with 9 kids.

Have you considered radiant ceilings? They can heat the floor by radiation and are also good with a low-conductivity floor covering. For a new build it seems to be worth consideration. This is theory only: I'd make up metal suspended heating panels rather than try to drive the heat through a conventional ceiling, which should allow a lower water temperature.

Radiant ceilings can also be very effective for cooling, but only if the internal humidity is kept low, or you would get condensation on the ceiling.

We do clip the dog's nails - the problem is the very hard and sharp grained quartzite sand in the local Oklahoma soils. The dogs go out and get it on their paws and then track it in - even though we have thick lawns and pastures everywhere. They dig . . . Doesn't help that they are big dogs as well.

A local friend, with similar size dogs and problem, uses commercial laminate and apparently this is a hard surface compared to wood floor finishes. No wear at all despite they have more dogs than we have, You are also correct that the so called luxury vinyl tile will work.

Wife really likes the newer ceramic planks - some of which look like wood - and those are also very hard. But that surface has high conductivity and can "feel" cold if not heated to high 70's to 80 F. Then problem of overheating air.

I have seen radiant walls and ceilings - in Europe. Floors make sense as was planning a thin concrete slab floor anyway.

In one home that I have visited (in a slightly colder winter than here) observes that the IR effect of a conditioned floor (72-73 F) is such that you can lower air temp to mid 60's F without feeling cold. I would agree as I never felt cold in that house. Talked to them this weekend and they agree that an air temp of 72 would "feel" way too hot in the winter. I hadn't realized that the air thermostat was set to mid 60's in that house.

In winters, we have very dry air and wife will complain that house "feels cold" unless the air thermostat is 73. This is largely due to the dry air. We do run a humidifier, as many people in Oklahoma do.

Got into trouble a few years ago when I "adjusted/tweaked " thermostat display to read 72 F when in reality it was set to 70 F. Wife brought home a temperature gauge and discovered that house was actually 70 F. So she then made me set the damn thermostat at 74 F. All my work/tweaking for nothing . . .

Has anyone used radiant flooring and then felt the need to lower the air temp to mid 60's F or so?


Steve

Hi Steve,

The benefits that you mention for radiant floors apply at least equally for ceilings. You say that the floor option makes sense as you were going to a concrete floor anyway. Since you are worried about having too much thermal mass, it would seem far more logical to eliminate the expensive, heavy concrete floor and go with the ceiling option, which has effectively no thermal mass, if you use a suspended metal radiator surface.

All solid, hard floors will feel colder than an air-containing material like carpet or cork, unless they are heated. Vinyl and wood are about 6 times lower in thermal conductivity than concrete or tiles however, I'm not sure if the difference would be noticeable. If you had ceiling radiant though, the very top surface of the flooring would heat up much more quickly with a low-conductivity material than the tiles would and this could become significant? Do you know anyone with a vinyl or wood bathroom floor who has heat lamps for bathroom heat to see how ceiling radiant would work?

Now that is funny!

Misunderstanding (of me explaining my situation). Thermal mass is good - up to a point. The key is to match the time lag/storage with the climate it is being placed in as well as the energy costs.

A heated four inch (10 cm) floor, throughout the home, may be simply too much mass for the climate here in Oklahoma. The problem is that we have a mild winter associated with a large rise in daily temperatures from nightime lows. In a colder climate, this mass volume could be perfect.

For compromise, a two inch floor might allow the right amount of heat storage without the long lag. If the time constant for heat loss is long, then you can end up releasing heat in the middle of the next daytime (overdamped).

Too short a time constant and the house temperature goes up and down (underdamped). Much like an impulse to a car shock absorber, the dampening must be correct.

I am running some models now, but it "looks" like two inches is about right for my mild winters and significant daily temperature rise (20-30 degrees F).

This article talks about time dependent thermal dampening concept . . .

Thermal Mass - Energy Efficiency of Concrete


Steve

You are married to a living precision thermometer!