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In-slab heating- -questions
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Author:  vpande [ Jun 13, 2007 12:33 pm ]
Post subject:  In-slab heating- -questions
We plan to build our new home with high ceilings and porcelain tiles. The builder will be providing ducted heating as standard. I am sure the ducted heat will stay on top with little effect on the cold tiles. As a solution we are wondering if in slab or under tile heating would be useful. I am wondering if
- we should solely depend on underfloor heating(and ask for credit for ducted heating)
- if we get underfloor heating is it enough to do it downstairs alone.(as thats the main tiled area)
-apart from $$ are there any other negatives- such as cracked tiles etc
Looking forward to your feedback
cheers
VP
Author:  Casa2 [ Jun 13, 2007 1:38 pm ]
Post subject: 
vpande,

I'm currently designing my house and I will be including floor heating. This will be the only heating in the house, except for a reverse cycle air-conditioner in the family room, which I hope will hardly, if ever, be needed.

The plan is to use hydronic heating pipes in the slab (PEX- cross linked polyethylene - very robust and last for over 100 years).

From there on, everything is different. No gas or electric heater. Instead I'm installing solar panels along the north roof. The more the better. Glass solar panels are about $500 each and "pool" heaters are considerably cheaper.

The idea is to run the water through the pipes during winter days (heating) and summer nights (cooling). To enable cooling the glass panels are not efficient since glass blocks heat radiation, which is why the (upmarket) pool heters will probably be best.

There are precautions:
1) Need to avoid freezing on winter nights (use anti-freeze or automatically drain pipes).
2) Need to avoid overheating on summer days (use pool heaters or circulate water through a radiator).
3) Need to ensure the floor does not cool below the dew point on summer nights or you’ll slip on the water (stop pump if floor temperature drops to (almost) dew point)

I have yet to find anyone that has such a system, but I can't see anything technically wrong with it.

Combined with passive solar techniques (high thermal mass, selective shading and night time ventilation), double glazed low-e windows and earth tubes+solar chimney, I'm aiming for the house to remain between 20 to 26 degrees Celsius all year round without using any air-conditioning or heating. Not sure if I'll succeed, but if I don't I'll be surprised.

Cheers,
Casa
Author:  Yak_Chat [ Jun 14, 2007 8:06 pm ]
Post subject: 
Vp,

Where are you? If you're thinking of traditional in slab heating, I have heard it tends to be not so useful in OZ because we do not have consistent long cold winters.
Ie we get some nice days, then some rotten ones and not months and months of really cold weather and as in slab heating takes time to respond, ie slow to get up to temp or down, so I'd review with others who have the system installed and see what thay say.

Typical issues are either sides of our winter you end up spending lots of energy heating the place up then opening doors to cool the place down, then when you have a cold snap one day and you want to warm the place up in a hurry it takes a while before it's up to heat again.

I saw a sustainable house (in Adealaide) that installed the british style of hot water heaters - ie wall radiaters that have hot water run through them, and you can valve off certain rooms etc, and it had a gas boiler and solar boost, (The lady was English) and her partner said it was OK in the dead of winter, but otherwise he said it bit too slow to respond for them when they wanted to turn it on or off for when they needed it on the Autum/spring time they had get all the water in the boiler hot, before it was of much use.

I lived in the UK for 2 and bit years, ie 2 winters, and we had the same hot water style of heating system which was also heated the winter shower /bath hot water (Yes they do actualy bath over there) :wink: and in the UK it worked treat as we would crank on the boiler in November ish, and turn it off in March April ish.

In each room you could valve how much heat came through by literally controlling the volume of water that flowed through the radiator.

I think casa's system willwork - time will tell.

I'm doing a similar system in my existing house but going to use my old solar hot water heater panel to preheat some water then run it through a wall radiator via a solar powered pump to pre warm the main living area during teh day as well as use sun heated air and solar pump that in to take the chill off the house - and on weekends when required I'll crank up the fire.

If you live in the snowy mountains, then I'd possibly go for infloor heating, but that not where you live, I'd be doing a big check that it's not more than you need.
Maybe a ducted would be more cost effective.
The tiles will always be cold unless you have the heat on all the time, and I do not think the under floor system would make them crack, unless you are allowing the temperature to bounce ie the concrete is expanding and shrinking often and lots.
My thoughts
Steve
Author:  vpande [ Jun 14, 2007 9:58 pm ]
Post subject: 
Thanks for your feedback Casa. I spoke to the builder and they have flatly refused to provide 'in-slab version'. if at all we will have to consider it after handover . I would still look at the undertile option especially in the tiled areas.. I remember seeing a DIY kit at one of the electrical place.I wonder how much power its gonna consume though... it appears like a wire mesh of heating elemet. Any ideas?
vp
Author:  Casa2 [ Jun 15, 2007 8:38 pm ]
Post subject: 
I would never use electricity or gas to heat a slab. It's just too expensive.

The wonderful thing about a slab is that it is a thermal battery. Charge it up with energy from th sun and let it keep you warm throughout the day and night.

The easiset way to heat the slab is direct sunlight from northern windows (shaded so that the higher summer sun does not enter the house). The more diffiult method is what I'm proposing (since living areas are on the south!) and that is solar panels to collect the heat and hydronic in slab piping to store the heat in the slab.

Hydronic heating takes a long time to heat the slab so it has to be "permanently" on during winter. Unless you get free (solar) energy, I think a reverse cycle split airconditioner would be the way to go.

Cheers,
Casa
Author:  stonecutter1309 [ Jun 20, 2007 8:21 am ]
Post subject: 
I was browsing and found this link to a hydronic system that may be helpful

http://www.enviro-friendly.com/hydronic-heating.shtml
Author:  Dobly [ Jun 24, 2007 3:21 pm ]
Post subject: 
Ok.. noob question here.. But why would you ever change the temperature of your infloor heating?

I mean, if you set the temp of your floors to say 17 degress Celsius.

If it was -2 degress outside, your floors would feel like a holiday in the bahamas...

If it was 45 degress outside, your floors would feel like a bath full of Paddle Pops. :)

I saw a system on an episode of Grand Designs where this chap ran a few hundred meters of piping a meter or two underground on his land, then under the floor of his house. The idea being that the temprature of the earth that deep down does not change much, therefore, the water pumped through the piping (by a relatively small pump) keeps the floors in the house at a fairly constant temperate..

All one would need is to run some sort of solar pump/battery setup and the the thing would run for years with no running cost.

This is a an option I am exploring.
Author:  Casa2 [ Jun 24, 2007 6:05 pm ]
Post subject: 
Dobly,

I would find 17 Celsius a bit cold in winter. Given that air conditioned offices are at about 22 Celsius, that would be, in my mind, the best temperature to keep a slab at if you could only select one value.

Keep me across your underground piping progress. I'm currently thinking of including earth tubes (which has a separate topic on this forum). These carry air through subterranean pipes and bring air close to 17 Celsius into the house. The problem is that the thermal resistance of the soil is so large that there is little reserve. It's more of a top up than a primary system.

Cheers,
Casa
Author:  Dobly [ Jun 24, 2007 9:59 pm ]
Post subject: 
Casa2 Casa2
Dobly,

I would find 17 Celsius a bit cold in winter. Given that air conditioned offices are at about 22 Celsius, that would be, in my mind, the best temperature to keep a slab at if you could only select one value.

Keep me across your underground piping progress. I'm currently thinking of including earth tubes (which has a separate topic on this forum). These carry air through subterranean pipes and bring air close to 17 Celsius into the house. The problem is that the thermal resistance of the soil is so large that there is little reserve. It's more of a top up than a primary system.

Cheers,
Casa


Casa

Here in Sydney the other night at our place, the internal temperature got down to 10 degrees in the wee hours of the morning in this rental house we are currently living in, with its horrendous lack of passive solar design.

17 would feel very snug compared to that and it would cost far less to heat the house up to 22 from there, than from 10 (or lower).

But I see your point. Having the underfloor system warming it to 22 in the first place would be better. Just a question of how much one wants to spend running the system.. In my case I love the idea of using the earth to heat (relatively) the floors of the house.

On that thought, i wonder if you could run the pipes under your compost heap.. That gets plenty warm. Would be a bit hit and miss but still, mmm.. I wonder if that would work?

Anyway, I'm looking at it, but I am concerned that it just might not be possible on my block of land.. it is VERY rocky. Would cost a fortune to get the trenches dug.

Dobly
Author:  Casa2 [ Jun 24, 2007 10:22 pm ]
Post subject: 
Dobly,

I'm putting my subterranean pipes in under the house before the house is built. I think I'll just need to go about 300 mm below the surface therefore rocks etc should not be a problem.

When are you building?

Cheers,
Casa
Author:  3timesbuilda [ Jun 25, 2007 9:05 am ]
Post subject: 
Dobly,

boosting the temp to 22C would mean that the slab would also warm and this would then be transferred underground. In effect you would be increasing your thermal mass. This may be a good thing but also may take too long, by the time you have raised the temp in your thermal mass, it may already be warming up outside.

Be intresting to findout.

3xb
Author:  Dobly [ Jun 25, 2007 10:55 am ]
Post subject: 
Casa2 Casa2
Dobly,

I'm putting my subterranean pipes in under the house before the house is built. I think I'll just need to go about 300 mm below the surface therefore rocks etc should not be a problem.

When are you building?

Cheers,
Casa


When am I building?? That's the $64k question. My wife and I along with our newborn baby are pulling up stumps in Sydney and moving up to near the land we just bought in Grafton.(Big move). Right now I am trying to secure work up that way... (not much chance of getting finance when one does not currently have a job). :)
I am a senior computer programmer, web developer type. I 'can' work from anywhere. Anywhere with an ADSL connection. In theory anyway.. I just have to get that organised before we can get finance. For now our priority is just getting up there and out of this horrible rental house we are in now in Blacktown. (Western Sydney)

You are putting pipes under your house? Interesting. The temperature 300mm under a slab, would not shift much year round, I would think.. Would be a great way to stabalise the temperature inside. Do let us know how your system goes.. When are you building?

Dobly
Author:  Casa2 [ Jun 25, 2007 12:40 pm ]
Post subject: 
Dobly,

I am finalising the house concept design at the moment. Should be ready to submit a DA to Council in a couple of month’s time. Would like to start building early next year, but at the rate I'm going it may be more like mid next year.

If you read some of my other posts you'll notice that I'm tacking on everything with regards to low energy heating and cooling. Not sure if everything will work, but it will be interesting to see what does and doesn't work. Will certainly let everyone know how well each component works.

My objective is to have a house that never goes outside the range 20 to 26 Celsius all year round without any air-conditioning or electric/gas heating.

If anyone has heard of any low energy heating or cooling ideas I'd be happy to try them and let everyone know how it performs. Low energy means only allowed to use power to move water or air around - no air-conditioning compressor or electric/gas heater.

Cheers,
Casa
Author:  stonecutter1309 [ Jun 25, 2007 12:55 pm ]
Post subject: 
Casa - I've heard good things about these for heating:

http://www.econoheatsa.com.au/
Author:  vpande [ Jul 06, 2007 10:20 am ]
Post subject: 
That website is good and those heating panels would be good in the bedrooms
if one can make them operate on timer switches.
Casa, I am getting quotes from a pvt builder who is willing to accomodate slab heating. The ones we had enquired was by 'devi' at a cost of approx $60 per sq meter grids into the slab.. I understand it uses off peak electricity to heat in the night and the slab then serves as a thermal battery..What was the passive source you mentioned? should one recirculate solar hot water? The issue with pvt builders is they dont like to make'box type' houses but I feel they are practical for placing solar panels. Please let me know if you know of any dealers for this type of heating
cheers,
vp
Author:  mek [ Jul 06, 2007 10:55 am ]
Post subject: 
This is purely from an amateur point of view, but did you notice in the supplied link where it is mentioned that these heaters are "designed to be on for long periods of time". To me, this is a bit like hydronic/in-slab heating where the reaction time is slower than ducted heating so it's not very efficient turning it on and off constantly.

I was speaking to our heating guy the other day, he's a hydronic heating specialist, and he says the same thing - I think even more so for in-slab as he says it takes approx. 8 hours until it's fully up at the desired temperature.

So I'm trying to put it gently into my Aussie husband's mind that the heating stays on while we go shopping. On low, of course, but on.

Another thing the heating guy metioned is that because we tend to turn our ducted heating on and off all the time it might contribute to cracks in the walls as the house cools and warms.
Author:  vpande [ Jul 06, 2007 2:48 pm ]
Post subject: 
Good info Mek. I have actually heard the weird cracking- stretching sound in a weatherboard home in the US whenever the heating kicked in ... one can imagine microscopic cracks that eventually become visible to the human eye.
Can you please provide the details of your heating guy, I can check them out on the weekend. I am also in Melbourne (eastern subs).
cheers,
vp
Author:  mek [ Jul 06, 2007 3:35 pm ]
Post subject: 
I hope you understood me correctly, vpande. I was talking about ducting heating in AUS where the turning on/turning off (and the cooling/warming of a house consequently) might contribute to cracks on walls.

If you're talking about cracking <b>sound</b> in the walls with hydronic heating, this comes from the water circulating in the pipes, as far as I know.

I have no details of the hydronic heating guy, his company is sub-contracted to our builder, but I can ask if you want.
Author:  Yak_Chat [ Jul 06, 2007 4:02 pm ]
Post subject: 
Mek - See my original post on this subject.
Unless you live in a constantly cold area - in slab heating - being a thermal mass based system - is better left on for long periods of time and it is not suitable for a on-off type environment.

You might find his link of help

http://www.energy-toolbox.vic.gov.au/dmdocuments/schools_information/secondary/secondary_supprt_matls/choose_heat_sys.pdf

Steve
Author:  FireFox [ Sep 20, 2008 2:06 am ]
Post subject: 
mmm on reading all there is on this forum about in-slab floor heating, i am still confused about cost/type and effectiveness.

we currently have gas ducted heating, and yes its quite effective at taking the chill off and then heating the roof often too hot and then no happy medium; without the system switching off and on constantly.

We are planning to build a large (well insulated/ICF) 2 storey house, with tiles on the ground floor and carpet upstairs, in Adelaide

Perhaps i think its a gimmick or the running costs that have me at a doubt, to me its sounds like a really big electric blanket; does it really 'heat' the room? or give you the perception of being warm/comfortable (like putting a beanie on your head) walking on warm tiles?

confused...

-Nathan
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