Underfloor heating. Advice, comments, experience etc

I am planning to use Durisol/Nexcem blocks as my foundation drop beams/piers, so it is a bit easier for me, as I will simply use 5 cm of Durisol (wood crete) material followed by 5 cm of XPS as the slab edge (replacing traditional wooden formwork during pour, too).

There are many other options available for alternative designs, e.g.:

http://www.laros.com.au/wp-content/uplo ... 150108.pdf

That's a good idea.

At the moment, I've poured my slab, however as side of the slab is uneven, it's pointless to attempt to add XPS between slab and brick veneer.

I may look at using some cans of expanding foam.. not ideal but better than nothing.

Mate, the do is, dont do it. Saves power great heating but just a hassle. If you live in Russia or Siberia good idea here in Australia and some carpet on the floor BONZA. And why even the garage ?

It's a hassle, but as you said great heating.

Did you end up installing it?

We’re extending our circa 1880’s home in the Adelaide hills late this year.
It’s not quite Siberia, but sometimes it feels pretty bloody close.
It’s in a gully only getting around 7-8 hours of sunshine in winter with temperatures as low as 10 degrees during the day and -5/6 overnight.
We average about 10 tonnes of wood through the combustion stove each winter, but would love to move to underfloor heating throughout.
Is it possible to run an underfloor system on solar? Say a 6kw battery system?

It is doable but do your sums. Calculate what your underfloor heating for your particular floor area would use to keep the rooms at say 22 degrees. Then work out how long that would last if being drawn from a battery being fed by a solar array.

Stewie

I don't think it will last long.

Personally, rather than use batteries to store electricity to heat up the slab at night, you'll be better off to heat up the slab during the day when the solar panels are proving free electricity,

One other issue with using electricity to heat up the slab is the cost of the reverse cycle hydronic unit.

That's kind of what I meant but I didn't explain it properly. I agree - use the power straight from the solar panels during the day and use the stored power in the battery at night. As per my first post - it depends how big an area ( X ) to heat powered by solar panels ( Y ) and battery ( Z ) to what temperature ( A ). Once you do those sums you'd be able to work out whether it would be feasible or cost effective.

Stewie

Thank you both for your responses.
There’s definitely so much to consider and it seems like each time I investigate an option another handful pop up. It’s hard to know which is the best way to go.
On top of under floor heating there’s solar cooling too? 🤯
Or perhaps pellet heat? I just can’t figure out what is going to be the most affordable, reliable, ecological way overall right now, but I’ll get there eventually.
Cheers again blokes.

I'm no expert, but everything I've read says electric underfloor is extremely energy hungry, of this is what you are talking about. Some people baulk at the cost of just running it in their bathrooms.

As Stewie says, you'd have to run the numbers. But I'm kinda interested, so will have a play around, in a non-expert way.

Like all electric element heaters, the element is considered to be 100% efficient, so 1kW of electricity produces 1kW of heat (though there will then be heat losses through the floor). Unlike heat pumps (like an reverse cycle AC), which can be considered to be 300-600% efficient.

Assuming the Adelaide Hills are much like Adelaide for solar PV, you'll average about 3.5 peak solar hours a day (for June & July). So a 6.6kW system should average about 23kWh a day in mid-winter.

A 6kWh battery system won't go far for electric underfloor. Which average between 100W to 200W per square metre. So say a small area like 10sqm is 1.5kW. Run that small area for 4 hours & you've used 6kWh.

Hydronic (hot water) underfloor heating can be much more efficient, when powered by a heat pump. Though the cost of the install can be very expensive.

Generally, reverse cycle (split) AC is considered to be the most efficient form of heating, with an economical install cost. But this is not for everyone (especially dust allergy sufferers).

Adding thermal mass may be a good way to get some thermal lag. Masonry heaters are a great way to do this when burning timber. You have short, hot, very efficient burns, which keep the room warm for many, many hours.

Thanks ddaroch, again input greatly appreciated!
The Adelaide hills are mostly much like the city, but Kangarilla-where we are- has a sometimes arctic like microclimate going on, because of the deep gully. It frequently looks like it’s snowed due to the coverage of ice on everything overnight.
And the house is old, built inefficiently too, but we’re getting that sorted with the reno.
I really hate the idea of burning fossil fuels for heating and cooling, so I think I’ll keep investigating. Surely there’s something out there that will get it done, I just haven’t looked hard enough yet.
Cheers again though 😁

Hi everyone.
This thread has been quite informative. I'm from Perth and am considering the best set up.

I'm looking to put hydronic heating through the area that's in yellow. (North is to the right of the page)

https://imgur.com/4BPOJiK

After a bit of reading, we've decided to do under slab as well as slab edge insulation.

The builder I've chosen hasn't done slab edge before. Exactly which part of the slab would need to be insulated to the edge?
I assume you would only need to do the edges that have the slab in them? There would be no need to insulate the edge to say the Activity Room on the right?

Thanks in advance!

Slab perimeter needs to be insulated. Ideally, you should be insulating slabs between indoor and outdoor areas as well as between your house and your garage.

If you insulate with XPS under slab, you can place under your footings too. In fact, in Europe, they form footings using XPS panels similar to how you form them with EPS void formers.

Thanks for your reply. Just to clarify, you would think it would be best to insulate the entire perimeter of the house, ie. down to the Guest and Across to the garage? Or just the perimeter of where the slab is being heated, ie. Kitchen, Dining and Living.

If you are investing into slab heating, why not to heat the entire slab? Incremental cost shouldn't be significant as the main costs will be around boiler, manifolds, not PVC piping and labor.

Good point. But being limited on budget.

Makes me think do we even bother with it. No point half doing it.