I decided to put a radiant floor in my basement back in 2007. We had just ripped out our stinking rotten carpet after two floods and were contemplating new flooring, and thinking about the dank dark cold underutilized space in our basement. Radiant was a good solution for us because:

  1. The most water resistant flooring is tile (thinking about possible future floods), and a radiant sub-floor would make the tiles delightfully warm instead of horribly cold. In retrospect, I’ve realized that our radiant floor has an intrinsic property that greatly enhances basement flood resistance, namely that water will run in between the original foundation and the foam layer of the floor, which allows it to run to the drain in our laundry room without ever being on top of the floor. This is true for retrofit slab-on-slab type installation, but generally not for other types of installation.

  2. Our furnace system has several problems which together fail to heat the basement: a) It is a single-setting furnace, with a single-speed blower, and the air output is always hot enough so that it floats up to the first floor without heating the basement. b) There is only one thermostat for the furnace, which is located on the first floor. c) There is a big difference in the number and size of vents between upstairs and downstairs, and the balance is quite terrible, and it’s impossible to adjust the vents enough to compensate.

  3. Redisigning the furnace and duct system to fix the above problems would be a very larger project in my house, involving a complete tear-down and rebuild. A radiant floor is actually easier, all other benefits asside.

  4. Radiant heating is slightly more effective than even the best furnace system, although with enough insulation and few enough windows all heating methods approach equality (because more insulation means less heating).

  5. Radiant heat using hot water could possibly be connected to a set of solar water heaters, which unlike solar electric panels are actually economically viable with today’s technology, and someday I want to have solar heating. However, in the end I decided this is not an important factor, and I believe that there will come a day that solar-electric panels will become a more cost-effective retrofit than solar-hydronic heating. (See below.) With today’s technology, solar-electric (photovoltaic) panels are extremely expensive and that isn’t true.

Chapter 1: The Floor

The first thing I did was plan my installation using the advice of the Radiant Floor Company. Wanting to be an upstanding citizen, I also got a building permit from Salt Lake City, although the permit was issued without final drawings. Then I ordered all the PEX tubing and special plumbing parts from the Radiant Floor Company.

I used the computer to layout the tubing and so that the lengths of the four loops were very close together. I believe I used Solidworks for this. (If you don’t have access to such software, I think QCAD would also work very well. Even Paint or GIMP can probably do this, but not very well. If QCAD doesn’t sit right for you, you might just fall back on paper and a ruler.)

I had removed the carpet and backing, leaving the concrete foundation stripped. First I laid out an inch of the pink foam from Home Depot and laid out my PEX tubing on top, and soldered a pair of copper manifolds and an air compression fitting to terminate the tubing and allow me to monitor the tubing integrity. I used 2x2 wood spacers (which are actually 1.5x1.5”) to set the thickness of the concrete sub-floor, and I used a Ramset (gunpowder charged nailer) to drive nails into the existing concrete foundation to hold the wood spacers down tight.

Tubing and Foam Copper Manifold

After bringing in the inspector to give me a thumb’s up on my tubing, I got my 5 gal bucket and 1/2” drill and started mixing up concrete on the patio, carrying it down the stairs, and dumping it over the tubing. By the way, this method sucks. My wife and I worked a back-breaking12-hour day on one section. We had three more sections left to go.

Bucket mixer Pouring concrete 1 section finished

Next I finished the other three tubing loops, brought the inspector in again, then I got a contractor to pump concrete into my basement and make me a slab. Having done concrete by hand already, I knew that this was the best $1,400 I ever spent. (If my wife and I had done it all ourselves, we could have paid ourselves around $14-16 an hour post-tax, which isn’t so bad, except for the nature of the labor.)

More Tubing More Tubing 2 More Tubing 3

Next I bought a $300 bridge wet saw from Lowes (which is by far the best tile saw available for this money), and proceeded to lay tile throughout the whole basement. We made this more complicated by placing accent pieces on every corner. Tile is a lot of work, but the end result is rewarding.

Completed Tiles

At this point the floor was ready to be plumbed, but then we had a baby. One year later, I saw the pipes sticking out of the floor and thought “oh yea, we have this radiant floor that’s almost done…”

Chapter 2: The Train Wreck

The city plans reviewer had made three comments about my plumbing diagram that I needed to address before I could do anything else.

  1. The PEX tubing needs to be rated for 180F at 100 PSI.

  2. I need to provide for the system to be drained out.

  3. The water heater needs to be rated for space-heating.

Of course the PEX tubing the Radiant Floor Company had sold me was rated properly, so that one was easy.

I had neglected to put a valve in the appropriate place for a gravity drain-out, but that’s an easy one to remedy because a blow-out is also acceptable, and just about any old compressor can do this job, and I did put shut-off valves on every tubing loop, which makes a blow-out operation more efficient.

However, I realized that obtaining a natural gas heater that would be rated for space heating was an issue, as the number of BTUs required would dictate that I replace my heater completely and create an intake from outdoors. This is notwithstanding the Radiant Floor Company technician I worked with was certain that my existing 40,000 BTU/hour heater would be able to do the job. Thanks a lot, Salt Lake, just ruin everything.

Furthurmore, I made some more realizations about my plan:

  1. Plumbing and placement of solar water heater panels as a retrofit project, including the solar storage tank and all the pumps and equipment that links the solar equipment into the radiant floor, factoring in the details of my old house, is a nightmare and there is no way on earth I will ever get it done.

  2. A plan that I formulated to design low-cost solar-electric panels would be much cheaper and easier to tie in if I use an electric water heater on the radiant floor.

    This might sound a bit crazy if you don’t know me, just let me say that I’ve run extensive calculations on my new concentrated solar-electric concept and I know I can make it work, also I think I can keep the cost between $0.50 and $1.00 per Watt ($4 per Watt is the best panel on the market right now - just a minute I think I hear some venture capitalists beating a path to my door… no it was just the wind). Anywas even if I’m not the one who invents this solar panel, somebody will, and most likely in the next 5-10 years.

  3. Using an electric heater, I can design a closed system that operates independent from my domestic hot water line, which also simplifies installation.

  4. Electric was good for me because I had a route to pull wires into the basement, but I didn’t want to add a vent or flue for another gas heater.

I realized there is another way to make a floor that would function the same, using resistive element mats. There would be some advantages, i.e. there would be no moving parts, the floor could have been thinner and cheaper (the mats could be laid in between 3/4” plywood and the tiles). However, I don’t feel bad about using a hydronic system, because electric mats are quite expensive per square foot. I’m guessing I would have saved around $1,000 on the floor and $700 on plumbing, but the mats cost around $10.80 per square foot, which would have run about $7,000 in my basement, so I’d have been over $5,000 behind with the mats. So overall I still think the hydronic system is better, even for electric heat. (Although the mats would be superior if I were doing a very small space, like a bathroom.)

Example electric mat

Chapter 3: The Plane and Battleship Wreck

Having decided I wanted an electric water heater source, I re-drew my plans, and took them back to my municipality to make sure I was in compliance. Also I needed to get a new permit because the original had expired.

My new plan was a closed system with an electric tankless water heater. This involved pulling a heavy wire in from the panel outside - but conveniently the pathway was through an unfinished laundry room. (There are times when I wish that all of the rooms in the basement were unfinished…) In creating this plan, I considered the worst case heat loss calculation of 16,000 BTU/hr and the amount of heat it would take to warm up my 1.5” concrete slab. Simple enough, I needed around 5kW for the maximum heat loss, at which rate the floor ought to warm up towards steady state in around 30 minutes.

I soldered up the pipes, connected the radiant floor manifolds, wired the new 6 kW heater. Finally with the floor “finished,” I confidently filled it with water using hoses from a nearby faucet in the laundry room, and switched it on… and… no heat. The pump was running, the water heater had power, but there was no heat. After some troubleshooting, I unhooked the tankless electric water heater and attempted to blow air through it with my lungs, and I realized what was wrong.

Conventional point-of-use electric tankless water heaters are designed to regulate water flow. The reason they do this is that if you were to open a conventional faucet all the way, the heater would be overwhelmed and you would believe the water heater didn’t work because you couldn’t feel any heat. By limiting the flow rate, the water heater makers prevent you from going beyond the very limited amount of power the heater is allowed to consume from the wiring, thus fooling yourself into believing your water heater was broken. (For example, at 5 gpm flow rate, a 6kW heater would heat the water 8.2 F, or from 55 F to 63 F, which is still quite cold.)

Although point-of-use water heaters do this, there is such a thing as a whole-house water heater which does not. However, whole-house water heaters are designed to consume incredible amounts of power and require quite heavy gauge wiring to deliver the power, but I had already installed a much lighter gauge of wire and I didn’t have large enough circuits or a wiring route available for a whole-house electric water heater.

The water heater I had installed therefore would require a very high pressure drop, probably at least 15 PSI and possibly up to 50 PSI in order to operate normally. After researching pumps, I realized this “feature” made my system unusable. My pump would be able to develop as much as 2 PSI, and maybe the best circulating pump would develop 10 PSI at 4 GPM. Fortunately when I calledStiebel Eltron and was referred to Energy Products, who produces customized versions of Stiebel Eltron water heaters, and I ordered the Hydro-Shark 3, which doesn’t not have any flow regulating features. Energy Products calls it a “micro boiler” instead of a “tankless water heater”, the big difference is that it’s designed for recirculating pumps instead of line pressure.

Once the Hydro-Shark 3 was installed, the system switched on and produced heat, which was exciting. However, after some more testing I realized the flow rate was still quite low, which caused the floor to develop hot spots and cold spots. So I went to www.mcmaster.com and bought a much more powerful replacement pump. With the new pump in place, the system finally operates at full capacity and it does a good job of it. One thing I like about the Hydro Shark is that it has a temperature regulator, which allows me to have some control over the floor temperature, even though I am using an air thermostat.

Chapter 4: The Finished Product

I can definitely say that the radiant floor is a superior way to heat a basement, or other two-story house, especially in comparison to the crummy furnace and duct-work in my house. Now I have a second zone, and the heat it produces is pervasive and effective. It’s also kind of nice to walk around bare-foot on the warm floor, although now that I have it I realize that is secondary.

The problem that remains is the thermostat, which is the air temperature type. A much smarter thermostat could be had using both air and floor temperatures to control the heater. Right now heat warmsthe floor, and the floor warms the air until it exceeds the set-point, and then turns off. But because the floor is still warm, the air continues to warm another degree before cooling down. By the time the air drops below set-point, the floor is pretty cold. So the space goes from being too cold to too warm and it doesn’t settle into a happy medium. The effect is small overall, only about 2.5-3 degrees total (whereas 2 degrees is normal for cheap digital controllers), and maybe not everyone would even notice it, but at some future point I may have to upgrade to a better controller. Possibly this may require adding a floor sensor, but I think a more advanced digital air controller also might be able to improve the system by shortening the cycles.

And here are the rest of the pictures:

Completed Tile Thermostat

Reflections

  1. Overall I’m very pleased with my floor. Warm tiles have a very nice feeling to them. The general “cold” feeling in the basement has been completely dispelled.

  2. I had some seepage last fall while some workers were tearing out some bushes in front (using a hose), and the floor was impervious. (This is what made me realize that the slab-on-slab installation allows water to seep between the old slab and the new slab instead of over the top. Other than bathroom leaks, I would get the same floor resistance with any other type of flooring.)

  3. My only point of dissatisfaction is the thermostat controller. If I did it again I would use an in-floor sensor, which I may even upgrade to later, if I can figure out how to retrofit post-installation. I may also try a more sophisticated air controller to see if perhaps the problem would be alleviated with shorter heat cycles.

  4. Electric heating is not a good economic or environmental choice in my area. I’m still plotting my escape to solar, although this could easily be 5 to 10 years down the road. Sad, but not overly expensive in the basement because the heat loss is not nearly as high as our first floor, also we use it only intermittently right now.

  5. Many of my complaints about forced air can be improved a great deal with a better furnace and better insulation. Having a zone for each floor and a variable rate furnace can greatly improve the effectiveness of forced air. Also humidity can be improved by having the furnace vented from outdoors or installing a whole-house humidifier. The furnace I have has none of those features. For me, replacing a furnace and adding a zone would not have been a good project, although I may someday see if I can add a humidifier and get a multi-speed controller board (I will not be replacing the whole furnace though).

  6. Hydronic radiant floor design is quite technical, and the design work I got from the Radiant Floor Company was critical. I think the prices they charged were very good considering the design was free. (There may be somewhat cheaper online sources for some items, but I would use the Radiant Floor Company again in a heartbeat nonetheless. They are very DIY friendly, which matters a lot in a project like this.) That being said, I did have technical issues this year that they didn’t help me with, but I’m willing to blame that on my sudden change in design, also it didn’t help that the technician who did the original design no longer worked there by the time I got back into the installation over two years after the outset. I can’t blame the company for something like that either. Overall I would give them a good recommendation for this project.