Slab heating advice: fact or fiction

[John G]

We are currently planning our new home, and are considering using slab heating.
In the research I've done so far, there seems to be a lot of mis-information about, so I'm asking these questions in the hope that those of you who have slab heating can answer them for me.

Can those of you who have slab heating let me know of your experiences.
What has worked well for you, and what has not worked as well as expected.

I've also added some of the stories I've heard, so I want to know whether there is any truth to them, or if they are all BS.

1) Is slab heating warm enough, or do you need supplemental space heaters for the really cold days?
I've read and heard that slab heaters only "take the edge off", and that they won't make a house toasty-warm. So that you still need some small heaters in the home to supply the extra boost. I'm in Melbourne, so I never get freezing nights, but yesterday for example the maximum was 9 degrees.

2) Does slab heating create hot spots in the room where the floor is covered? e.g. under sofas and cabinets?
I've heard stories of sofas getting so warm that they are uncomfortable to sit in. Is this true or a myth?
I've also heard that when laying out the cables/pipes, people purposely leave empty the areas they know where cupboards and wardrobes are going, so that they don't overheat.

3) Can you use floating floors with slab heating?
The first problem is that the floating floor doesn't allow the heat to transfer. Because floating floors are laid on a thin foam membrane, this effectively forms a thin layer of insulation, and so traps the heat under the floor. So you have to turn the thermostat up.
But the second problem is that the warranty of laminate flooring is voided if they are overheated. The solution to this is to use a thermostat with a floor probe. But then this results in a colder floor, which combines with ther first problem, really making floating floors unsuitable for heated slabs.

4) Is gas hydronic the cheapest form of slab heating to run?
I've read that the worst heating method (from a cost and efficiency perspective) is electric cable heating.
The best heating method is hydronic tubing. The water can be heated either by an electric heat-pump, or by a gas boiler. The cheapest to run is the gas boiler.

Thanks,
John.

[dazzler]

Hi john

we had slab heating when we lived in blackmans bay tasmania and it cost a heap to run. The thermostat light was nearly always on and the meter spinning so fast that it was a blur:p

It was a rental so maybe it wasnt working right or something so wouldnt want to make a blanket statement about all in slabs.

http://www.warm.com.au/images/newphotos/ceiling_heat/ceiling5.jpg
We had another place that had in ceiling heating which
sits on top of the ceiling plaster and is thermostatically operated in each room.

This was way warmer and actually used to toast my hair challenged head.:D

Its not cheap around $350 per square (not m2)

Our next place we build will have this sytem. here is a link.

http://www.warm.com.au/pick_a_topic/heating/ceiling_heating.html

cheers and good luck

dazzler

[Greg Q]

We had in floor hydronic heating in Canada, worked very well on an insulated slab, and was no more costly to run than an average house with ducted heating.

I wonder about the lag time required to heat the slab- it often seems to me that in Melbourne, instant (ducted) heating is required in the morning, then by 11:00 or so the day is warm enough to turn it off.

I still may opt for ducted in our next house, but will include provisions for in line air filters to eliminate the dust problem.

(Does anyone know why filters aren't normally fitted here? They have been standard overseas for forty years or so)

Greg

[Auld Bassoon]

I've often wondered about that too Greg. It seems, to me at least, that a filtration system would be essential, but in all the houses that I've lived in here in Aus. with ducted warm air, not one has had a filter????

[ozwinner]

I've often wondered about that too Greg. It seems, to me at least, that a filtration system would be essential, but in all the houses that I've lived in here in Aus. with ducted warm air, not one has had a filter????

Thats 'cause our air is pure.

Al :D :p :) :rolleyes: :cool: :confused: :o :eek: :( :mad: :mad: :( :confused: :o :eek: :D ;) :p :) :rolleyes: :cool:

[Groggy]

(Does anyone know why filters aren't normally fitted here? They have been standard overseas for forty years or so)I could hazard a guess. Since it is not mandated they leave them out - anything to make a buck.

[Greg Q]

I could hazard a guess. Since it is not mandated they leave them out - anything to make a buck.

I guess. But the filters I'm talking about are throw-aways, buy a new one every six months or so for $5.00. In fact, I think I could whip up a frame at the cold air return grille to hold some filter cloth in a stretched frame for a few bucks, might be a big improvement.

If you google "furnace filter" you can find permanent, washable and electrostatic ones for more money.

Greg

[ROB NZ]

Hi John,
We have electric underfloor (consrete slab) heating in our house, and haven't had it on for 4 or more years. The cost is simply unsupportable for us, even though there are thermostats in each room. When we used it we would only have it on for low level heating, - about 12 to 15C and for a higher comfort level would add fan type electric heater in specific rooms.


The main thing to remember about heating in concrete floors is the very long lag between switching on, (or the thermostat switching on) and the resulting warmth reaching you.
We felt that we were heating the house for long periods when we didn't need it.

I am aware that modern electronic control systems give a greater level of control.

Three years ago we installed a Jotul (Norwegian manufacture) wood burning space heater in our otherwise unused fireplace. It heats the main living areas of the house quite adequately, - the lounge cosily, and has the added benefit of keeping me fit chopping wood and clears our property of unwanted trees and branches.
We are delighted with it.

A few years before I retired I was instrumental in getting a single storey office building constructed where I worked, with an underfloor hot water/gas fired system installed. Once they got the control system and zoning sorted (more heat to south facing rooms, less to north facing) it worked quite well, but we tended, (and they still do) to run the system warmer than you would at home. Its easier for some one whose room is too warm to open a window than to put up with the moaning from someone who perpetually complains of the cold!!!

Of course in that case it is not a private pocket that pays the utility bill.

As the old saying goes, "Yer pays yer money and yer takes yer choice."

ROB NZ

[Groggy]

I guess. But the filters I'm talking about are throw-aways, buy a new one every six months or so for $5.00. In fact, I think I could whip up a frame at the cold air return grille to hold some filter cloth in a stretched frame for a few bucks, might be a big improvement.Greg, I know what you mean, I lived in the US for 4 years myself and we had them in our house. I still think they are trying to save a few bucks. When you guys were watching colour TV we had people trying to sell us coloured plastic filters to "convert" our tvs to colour :rolleyes: . They just moved on to house heating is all. Oh, and removalists. Look up day-release workers on google and you'll get a match on Australian home heating and removalists. No, really, you will :cool:.

[Greg Q]

Greg, I know what you mean, I lived in the US for 4 years myself and we had them in our house. I still think they are trying to save a few bucks. When you guys were watching colour TV we had people trying to sell us coloured plastic filters to "convert" our tvs to colour :rolleyes: . They just moved on to house heating is all. Oh, and removalists. Look up day-release workers on google and you'll get a match on Australian home heating and removalists. No, really, you will :cool:.

Yeah, tell me about it. I have engaged removalists a couple of times. It always makes me feel like I have been mugged, only without the good bits.:eek:

[silentC]

We had a 7kw and a 2kw cable in our place. It was wired to off peak, the idead being that it would heat up over night and retain the heat during the day. It worked pretty well but we needed a space heater as well on the colder nights (this was in Sydney).

Probably the biggest disadvantage was the lag time. It takes ages to heat up (being off peak, you turn it on and it does nothing until the next morning) and it takes ages to cool down, so if you get a warm day after a few cold ones, it can be pretty stuffy for a day or two.

We thought about putting it in the new house but decided against it, mainly because of cost and the inflexibility.

[DanP]

If you want hideously expensive, next to useless heating for your house, get it. With my winter power bill, I could pay for three quarters of a gas central system. It's cold at night and stinking hot during the day but you can't turn it off coz it takes two days to get back up to speed again. So if you want my opinion;

DON'T DO IT

Dan

[John G]

Thanks for the replies so far (except for that tangent about duct filters...)

For those of you who've had this kind of heating previously (dazzler, greg, rob, silent c, dan):

Hmmm... you aren't overly positive about your experiences. Clearly with this type of heating, insulation is a critical factor because the aim is to maintain a constant temperature, regardless of the time of day.

You all seem to be confirming that electric slab is expensive to run, which matches what I've read. The off-peak is especially problematic, because it only runs at night, and if the house isn't super insulated, you lose all your heat by the evening. So if we go slab heating, we will definitely be going hydronic. Probably gas, because this is cheaper to run, and can be run at any time.

Did any of you have timber floors in your homes, and was this a problem? I was at a flooring place on the weekend, but the guy had no idea.

And Greg, with the hydronic in Canada, how effective was it against the canadian winters? Presuming the house was properly insulated, did it cycle through being too hot during the day, or too cold in the morning? Did you need extra heaters, or was hydronic it? And if the heat was cranked up, did you get hotspots under the sofa etc?

I'm now wondering whether this heating is really best suited to really cold climates (europe, Nth America) where you don't get much warmth during the day. It's true that in Melbourne, you usually need a quick boost in the morning, then use it only occasionally during the day. Or maybe I am just used to this because I have used ducted gas for so many years.

This is a pretty major decision when building a new home, and I'd hate to install slab heating, only to regret it later. It's not a small investment. So any further experiences would be welcome.

John.

btw - my old place in canberra had a filter on the ducting intake, but my current place in melbourne just has a hole. I am sure it's just cost cutting by the installer. I'd hate to see what it has done to the fan and motor. Out of sight, out of mind eh?

[rrich]

I'd hate to see what it has done to the fan and motor. Out of sight, out of mind eh?

Oh the allergies!

Here in Huntington Beach, the lowest temperature is in the mid fourties. (Would that be about 8 C?) We have forced air. (Gas heats a plenum and the air is forced through the plenum and then through out the house.)

The interesting thing is that last year we increased the size of the house by 50% and reduced our natural gas costs by about 50%. It's all about insulation. R-30 in the ceiling and R-19 in the walls of the addition. We also added the R-30 to the old part of the house.

My advice would be to go with the forced air system and as much insulation as will fit into the space available. Consider Low E windows too. They really do make a difference.

[ozwinner]

R-30 in the ceiling and R-19 in the walls of the addition. We also added the R-30 to the old part of the house.

.

Assuming the ratings are the same, thats funny. :D

We talk about R3 here, and here you are talking about R30. :D
I shall never complain about being cold again.

Al :p

[GraemeCook]

It's all about insulation. R-30 in the ceiling and R-19 in the walls of the addition. We also added the R-30 to the old part of the house.


Rich is using the American R-system - just divide by 5.78 to convert. So American R-30 and R-19 are the same as the metric R-5.3 and R-3.3 respectively.

We also lived in the States - in Boston where temperatures hover around ten degrees farenheight below freezing from Christmas to Easter - and had an oil fired hydronic system. There were small skirting panels about 2 000mm x 200mm x 50mm under each window. They heated the house uniformly in about 15 minutes; silent and no fumes or drafts. Walls had about 150mm insulation plus clapboards and triple glazed windows.

This was a very effective system, comfortable and easy to use.

We looked at doing similar in Australia but the equipment does not seem to be available. All advertisers of hydronic systems seem to be concentrating on the commercial market only.

Cheers

Graeme

[silkwood]

We've had underfloor electric and hated it for all of the aforementioned reasons. Even the newer electronic contol systems can't overcome the lag problem We now have ducted gas (including filter!!!) and love it. With a tiled floor you get some benefit of the maintained heat concept but without the downside. Needs good insulation to be most effective though. Worst part is there is no visible heat and I keep forgetting to turn it off! (yeah I should set the auto controls but I keep forgetting that too! Maybe I should do it now? Oops, news is on!)

Cheers,

[Guy]

Have you considered placing a slab then laying polystyrene sheets with slots cut in for polyproperlyne piping, which gets run off to a furnace somewhere. You can set it up so each room has there own set of controls which pump the water around. Then you can place either a floating floor or timber on top of it all.
Saw it on Lifestyle channel about 2 weeks ago, UK prog about these idiots building there houses, also This Old house has used something similar

[Grunt]

I'm going to put hydronic heating in our house when I actually get around to build it.

We're going to use a Quantum hot water system which is a heat pump heater. It's very cheap method of producing hot water and it produces hot water year around, day or night. It will produce 800 litres of hot water a day.

The Quantum won't have the power to do the whole house but I'm only going to heat the living areas.

Quantum Energy (http://www.quantum-energy.com.au/Products/CompactSolarHeatPumpExplained/tabid/264/Default.aspx)

Combined Slab Heating & Hot Water
(http://www.skylineenergy.com.au/water_heaters_slab_domestic_340TIH.php)
Chris