Grey Stone - Sustainable Eco House

listed by What Power Crisis?

underfloor heating with concrete slab 

how thick should the slab be for underfloor heating and what type of piping is used for wetback to underfloor and what kind of pump?

Re: underfloor heating with concrete slab 

The best method is installing the underfloor heating
into 50mm overlay concrete with insulation between the overlay and the slab.
This method is slowly coming in NZ and already done for decades in Europe.

It has three major advantages:

Repair or replacement of the pipes is easier. With the pipes in the slab replacement is pretty much impossible.

The floor temperature can be easier adjusted to changing conditions and less heat loss.

Other services can be accommodated in the floor

Re: underfloor heating with concrete slab 

Hi bj,

We were originally going to go with underfloor but have decided against it (v.expensive for the mount of heat you get out, too slow to heat up etc) we went for wetback and rads throughout in each room.

Specific to your point though, to ensure you get the most out of your underfloor system, it is important you ensure you instruct your builder to adequately insulate the slab.

A simple layer of 50mm thick polystyrene under the main part of the slab, probably won't do enough and surprisingly BRANZ have done some research (based on some US research I think) that an increase in the thickness of EPS (Expanded PolyStrene) underslab does not automatically lead to an R-Value increase.

of course hot air rises, but it will also find its way quickly to where the resistance is least (rather like an electric current) this means properly insulating around the perimeter of the concrete footings as well as underneath them, or at least slowing the transfer of heat from the main slab to the footings by means of a piece of insulating material (usually a piece of timber) that sits between the slab and the perimeter footing.

This is easier said than done and having gone through the whole process with our builder, there are only a small handful of accepted techniques for doing this and all were out of our budget (We simply put more money into the CH system and over-insulating walls and ceiling instead)

There have been several good-length threads on EB about exactly this, have a search through the forum archives.

As for the type of pipes to be used, I think plumbers these days can still use copper but its price varies often due to international market fluctuations. The other types are "Fusiotherm" (A type of plastic snap-together pipe made in Germany and in regular use in NZ) and another of some aluminium composite, who's name escapes me.

Good luck :-)

Re: underfloor heating with concrete slab 

Very interesting re: the slab insulation, I observed a new house being built over a number of weeks just over a year ago, the slab was poured with under perimeter insulation only around the edges, none was applied to or under the footings or to their external facings. The hydronic heating will be loosing much of its heat and be very inefficient; this place is being sold and marketed as an eco show home. I wont name the company who built it, but it is very obvious shortcuts are being taken by the big players and its the hapless purchasers that will be carrying the problems.

Re: underfloor heating with concrete slab 

Where is the hint about the David Reid Home???
The censorship is getting a bit over the top here
:-((
Regards from China, the land of free speach!!!!

Re: underfloor heating with concrete slab 

To all anonymous users here:
Any chance that you create a login, login, or at least state your name so I can differentiate between all of you? Lately, more and more posts became "anonymous", which is a wee bit irritating.
Are you all afraid to mention your name?

Kindest regards,
Ingo Ratsdorf

Re: underfloor heating with concrete slab 

Ingo Ratsdorf

The building industry in this country is so dirty, nasty and corrupt that we need to watch our backs.
Especially those who are outspoken about the state the building industry is in.

K

Re: underfloor heating with concrete slab 

50m overlay is not the best system for New Zealand. NZ has relatively cheap electricity and relatively expensive gas - hence the cheapest form of heat is via a hot water heat pump.
But this is an energy storage system rather than a heating system - and enough energy can be stored in a standard 100mm slab during the day with a 12kW hot water heat water heat pump using about 2kW an hour- for 4-12 hours a day.
JK

Re: underfloor heating with concrete slab 

Nonsense it works well overseas it works well here.
Especially with the ever changing weather it offers flexibility and much better efficiency.
If you use the whole slab as energy storage how do you control the temperature of your floor when the weather changes?
Electricity cheap in New Zealand ? You must be kidding :-))))
The whole building industry keeps saying that we have to do everything different here (maybe because we are upside down !!!!)and the result is mostly disfunctional and inefficient crap

Re: underfloor heating with concrete slab 

@K: Noted, but not necessarily agreed. ;-)

All right, initials are fine. As long as I know that it is not all the same person.

Cheers,
Ingo

Re: underfloor heating with concrete slab 

My slab was poured yesterday 8th February 2010 with underfloor heating pipes embedded, so heres what I did.

6-9 months ago I got quotes ranging from $14K to $24K for UFH system coupled to a hot water heat pump (search archives for details). The systems offered varied in price/quality/technology so it was difficult to compare.
In the end I decided to design my own system using information provided by http://www.underfloorheating1.co.uk and http://www.eco-hometec.co.uk/heating_downloads.htm. (aside: why is NZ so secretive when it comes to info?)
There is a pipe layout design package (free trial) available from http://www.avenir-online.com/LoopCAD/LoopCADMain.asp?Page=TrialVersion
There is a company on trade me selling PEX piping for UFH. I used them for all piping and manifold components - so far spent approx $2600. Will purchase heat pump at later date. Installed the pipe myself with help of some friends. I am installing the European way, i.e. pipes clipped to poly not tied on top of mesh, clips sourced from UK approx $70.

Regarding slab/foundations and insulation. The NZ building code and 'standard' building practices make it very difficult to achieve a properly insulated slab to European levels. If money was no object then I would do a structural slab, insulate the top and the pour a heating slab, however for cost reasons and NZ codes I have had to compromise. The foundation walls are block construction, I have put 100mm poly beneath the slab and intend to externally insulate the walls with 25mm poly and a plaster finish. Have a look at the design navigator website forum, there is some discussion there regarding slab insulation.

The plan is to run the system 'long and low'. I.e. it is not an instant warm the house heat (the wood burner will do that), but it is to provide a level of background heating so that I don't have to get up to 12C bathroom each morning.

I'll post some photos later when I get home from work ;)

Pete

Re: underfloor heating with concrete slab 

Underfloor heating there is not a right or wrong way,
It how it is applied and what your expections are.
In this case the OP whats to use a wet back. So he needs a quick response time, (one presumes he does not spend all day and night stoking the fire) So pipes mounted close to the surface is better.
Is he being energy efficient "no" why because most of the fires energy is at the ceiling, not much use up there. Better to use an air transfer system, no the crap from the retailers. Draw air from the ceiling (where the fire is) Inject the warm at "LOW LEVEL" into each room. temp can be controlled by air damper or individual fans to each room.
Re slab insulation, most energy from underfloor heating is lost sideways not downwards, hence only insulation at the edges. having full insulation is of course better that not having it. But do not get hung up about it. When designing I tend to keep the pipes away from external walls. This by itself reduces external losses.
Running time, a house needs 'X" amount of energy a day, if you run a system 24hours or 10hours, still the same amount. A system has indirect benefits, basically set temps are normally lower than on/off systems, thus losses are lower. It is all about comfort
TC

Re: underfloor heating with concrete slab 

Agreed no right or wrong way, just depends on what your trying to achieve.

Couple of boring photos of what I did, as I said earlier insulation to exterior block foundation will be added later.

Pete

Re: underfloor heating with concrete slab 

Photo with more detail

Re: underfloor heating with concrete slab 

A really easy way to insulate the perimeter of a foundation for new construction is to use ICF (Insulating concrete formwork a.k.a. poly blocks) rather than concrete masonry or timber boxing, and then plaster finish.

Then if you use 140mm timber framing you can overlap the bottom plate with the polystyrene formwork to minimise thermal bridging.

Re: underfloor heating with concrete slab 

Hi Pete

Interesting photos: Is the reinforcing laid directly on top of the pipework, or is there a spacer to raise it slightly higher?

How thick did you make the slab?

Seeker

Re: underfloor heating with concrete slab 

Hi Seeker,

after these photos were taken the builders placed the chairs to raise the mesh. The slab thickness is 100mm. There are some slab thickenings where load bearing walls and columns are needed. UFH heating pipes to not run in these thicker areas, where the pipes needed to cross the thickening I ran it through conduit, it also ran in conduit where it crossed a slab cut. The pipes in the longer conduit run along a corridor to another set of rooms, I shielded the flow pipes to try to reduce the amount oh heat given up in the wrong part of the slab.

Pete

Re: underfloor heating with concrete slab 

Pete - your heating pipes appear to be taped to the polystyrene insulation - so you are heating 100mm of concrete?
Whereabouts in the country are you building?

Re: underfloor heating with concrete slab 

Hi Cam,

The pipes are clipped to the poly using U shaped barbed staples approx 40mm long. These clips are really meant for foil backed polyurethane boards (such as kingspan) but these boards are expensive in NZ compared to polystyrene. However, a small length of duct tape prevents the barb from pulling out of the poly, so that is the tape you can see in the photo.

You are right anyway, I am heating the full 100mm from the bottom. I know that we will get a lag from switch on to useful heat output to the room, but thats ok, the idea is to provide a background level of heat. We had UFH in our last UK house before we moved to NZ so we're used a system like this. If we wanted quick heat I would have gone for panel radiators running off a wetback. As I've also mentioned in other posts we're using 250mm thick Cornerstone panels for the external walls (my builder jokes that he's making a large chilly bin), so we're hoping the heat will be retained nicely.

We are building on a rural block about 3k northwest of Masterton.

Pete

Re: underfloor heating with concrete slab 

pipe clips

Re: underfloor heating with concrete slab 

for those looking for an integrated floor/wall/midfloors system with continuous insulation check out: maxsystem.co.nz (Queenstown)
I hope to build my new house in Wellington with this system soon. The input from and dealings to date with owner Sam have been just fantastic! I am still undecided about the underfloor heating and HW system (with HP) any suggestions are welcome as the company I am dealing with is constantly changing its suggestions. Marcel

Re: underfloor heating with concrete slab 

We sorted out our combined underfloor/hot water heating system early last year. For a 200 sq m house the cost is usually $14,000, split about $8000 for hardware and $6000 installation.

One hot water heat pump outdoor unit, warm house in winter - low cost hot water all year.

kippingheating.co.nz

JK

Re: underfloor heating with concrete slab 

Hi, we will shortly be building a single storey house in Lake Hawea, and I have been going round in circles trying to sort out the best way to insulate the perimeter of the slab.
We are putting pipes into the 100mm slab with the hope of eventually setting up a hot water HP underfloor system, we will have polystyrene under the slab and are using polystyrene blocks for the slab formwork.
My question is: what is the best way to avoid thermal bridging out the bottom of the footings? I've attached a diagram of the system as it has been recommended to be used but I think that we may lose a lot of heat out the bottom of the footings. Can anyone recommend how we avoid this?

Re: underfloor heating with concrete slab 

sorry wasn't actually able to add the diagram, but if you're really keen you can find it by downloading a large pdf from the Superform website www.superform.co.nz
I forgot to mention that we are having 140mm frames on the external walls but I don't understand how overlapping this with the formwork stops the heat escaping out the bottom?

Re: underfloor heating with concrete slab 

Nicky,

have a look at/ read through
http://www.design-navigator.co.nz/phpBB3/viewtopic.php?f=6&t=8

Yes you will lose some heat but I would not stress about it. The way to lose the minimal amount of heat is to construct the slab fully insulated as they do in Europe, but this hasn't caught on here as it tends to be more expensive. Unfortunately, the building codes are heavily skewed toward earthquake (for good reason) but to the detriment of energy efficiency.

Pete