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stevehull 08-12-16 11:07 AM

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.


DEnd 08-12-16 05:07 PM

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.

stevehull 08-12-16 05:17 PM

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?


DEnd 08-12-16 06:49 PM

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).

JRMichler 08-15-16 08:17 PM

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.

stevehull 08-15-16 10:15 PM

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.


ksstathead 08-19-16 10:27 AM

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...

stevehull 08-19-16 11:52 AM


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 . . . . .


philb 08-20-16 02:45 AM

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.

stevehull 08-20-16 05:32 AM


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!


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