DIY Hydronic Floor Heating

Hi Guys, what an excellent DIY thread. I wish you guys were working for me!

Just to be helpful, here are some guidelines we use that may take some of the mystery out of certain things discussed here.

Hydronic–in-slab:

The Do’s:
1. Use 100mm to 150mm (4” to 6”) spacing in the slab with 10 and 15mm pipes respectively. Make sure the Pipe’s bend radius is not exceeded by these numbers. 150mm (6”) thick is best for added thermal mass.

2. Make sure the pipes are at least 50mm (2”) deep in the concrete, preferably above the metal reinforcing screen

3. Make sure the pipes are suitable for direct burial in concrete and that it is designed for this type of heating purpose and that the pipe is oxygen proof.

4. Don’t ponder the antifreeze issue, if you need it, and most of us do when using a solar offset, use it - the efficiency will not materially impact on the heat transfer in a real world. Make sure pumps and pipes are OK with this additive. Don’t use Car antifreeze as the additives can be detrimental to long term usage.

5. Don’t use XPE under a slab, use HDPS (High Density polystyrene). Always use it, we use 140mm (6”) but 90mm (~4”) would be the minimum we recommend. The house will not settle on this stuff. I have seen a concrete truck drive over this stuff with hardly as dent.

6. Don’t use small diameter pipes over 100M (330’) in one go.

7. Lay the pies intelligently, don’t try to heat places that don’t need it such as under counters, under larders/pantries, but do include clothing closets.

8. Design the pipes to provide warmth to the bathroom(s) first, and in BR the warmer temps should be on the perimeter. Stay away from piping close to the outside wall by about 400mm (Just over a foot) to avoid heating the wall losses unless that spot is regularly walked upon.

9. Don’t overheat the pipes, you are generally aiming for a 30c (85f) max floor temp in an energy efficient house. More if not. No warmer than 45c (120f) or you add to long term risks. At 30c you are about the same as a warm summer day and things like wooden floor coverings rarely have issues.

10. ALLWAYS insulated the edge of the slab!. You will lose easily 30% of your heat there in sub freezing temps and much more as the temps go down. We use ICF perimeter with added HDPS to achieve 100mm of insulation – minimum.

11. Hot water heat pump for back up is a good idea. We retail a 9kW unit to our clients, good down to -15c (5c) for about USD$ 2.8k You should be able to find similar deals in your areas. This will heat a 200SqM (2100SqFt) proper thermally efficient EE home down to about -10c (0f)

12. Insulated any through pipes (Toilet tacks etc) and stay away from these with your pipes.
13. Geothermal Heat Pumps: Lots of good and bad things about this, some of it is common sense:

a. Horizontal type: Stay well away from flower beds and trees as the ground around these pipes will freeze solid at the height of cooling.

b. Horizontal type: Stay way from paved driveways or you will turn them into Skid pads when there is no serious insolation.

c. Vertical: Keep transfer legs short and common sense insulated.

Hope this helps. Obviously much of this is averaged and some will be in colder places than other, so use some common sense.

John Guest company (UK) make a decent spreader plate to be stapled under existing wooden subflooring.

Stay Warm!

Cheers,

Ron Theaker CD
GM
Digital Self-Heating Homes