How to best heat the SLAB ?

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How to best heat the SLAB ?

Postby Wirregar » Tue Sep 29, 2009 12:13 pm

I have a Late 80's house that has a very large SLAB floor. When built they put Hydronic coils in the slab to heat it. This can currently be fed by Gas (a very large, expensive to run LPG Furnace), or via Wood (An old Wood fired furnace which is on it's last legs).
The water is then pumped around the slab by a Pump (Again too large and inefficient for it's intended use).

Problems are;
The Gas fired furnace is old, needs an overhaul, consumes too much Gas and very expensive to run
The Wood furnace is old, Does not regulate heat / burn rate, is a PITA to load and refuel (Read burns face and hair when you opent he furnace door) and startign to break down internally and I no longer trust it.

So my two heating methods are no longer viable, and therefore we have zero heat in the house apart from one very small wood fire heater.

What would be the best way to re-engineer the slab hydronic heating?

A new modern Wood furnace?
Some sort of heat pump storage fed system?
Geothermal (I have lok ed into this and it seems a very expensive install option)

Something else? I am open to all suggestions.
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Re: How to best heat the SLAB ?

Postby Millsy » Tue Sep 29, 2009 3:19 pm

Hi Wirregar

You have a bit of a problem on your hands :S. As far as i know new heat pumps are quite expensive to buy and to run, so i would look at alternative options.

Your easiest option would have to be putting new high quality carpet down, with high quality well insulated underlay. this will make quite a difference for your comfort level in some rooms.

your other possible option depending on your house structure and site, maybe to have large North facing Windows to allow winter sun to warm the slab, this is released slowly through the day and night. This type of heating is called passive solar heating, this can be surprisingly effective.

Combined with double glazed windows will make quite a difference to your overall need for heating or cooling.

Hope this gives you a few more ideas.
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Re: How to best heat the SLAB ?

Postby Millsy » Tue Sep 29, 2009 3:30 pm

Hi Wirregar

I also like the idea of using a heat pump hot water system for heating the slab as they work with the reverse method to a fridge, these will heat 24 hours a day every day of the year, they are also meant to be quite economical to run. This perhaps could be a good option for you.

Also you may be interested in a new Modern Hydronic heating system since you already have most of the structure in place. there is a company in Melb that has decent information on what they say are the most efficient modern systems http://www.hydronic-heating.com.au/

hope that helps.
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Re: How to best heat the SLAB ?

Postby Wirregar » Tue Sep 29, 2009 3:47 pm

Millsy wrote:Hi Wirregar

I also like the idea of using a heat pump hot water system for heating the slab as they work with the reverse method to a fridge, these will heat 24 hours a day every day of the year, they are also meant to be quite economical to run. This perhaps could be a good option for you.

Also you may be interested in a new Modern Hydronic heating system since you already have most of the structure in place. there is a company in Melb that has decent information on what they say are the most efficient modern systems http://www.hydronic-heating.com.au/

hope that helps.


All good suggestions, If I was building, I'd be doing all that, but not an option in this case; (maybe I sould put in some more background)
The house is already built as previously mentioned;
There is some carpet already in the bedrooms and lounge, but hallways and kitchen is tiled
The windows are not double glazed (And at the current cost will never be)
This is a LARGE double bricked country house with about 20 metres of floor to roof windows along the west wall - Built for views, not heating efficiencies.

We have to work with what we have, and what we have is a hydronically heated slab (There is also hydronically heated ducted sytem in the roof, but I am not that interested in that option at this stage)

I am looking for alternate heating methods for the hydronic slab heating. geothermal, Heat Pump, new wood fired furnace, or anything else that you guys can recommend. I am open to options, but price to install is also a factor.
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Re: How to best heat the SLAB ?

Postby grahamn » Tue Sep 29, 2009 10:22 pm

Unfortunately I don't think any of the options are cheap...
You didn't mention size exactly but "Big House" makes it hard also.

Replacement Gas boiler probably cheapest but costs a bucket to run.
Heat Pump in large house you would be looking at upwards of $10k, add another $10k at least for ground source but both could heat water into your current infrastructure.

Depending on where you are solar evacuated tubes into a storage tank (or possibly without tank depending on the slab thickness/insulation properties) might be the most economical in the short and long term, particularly as you already have the tubing in slab!

There is a reasonable resource page on the energy matters site http://www.energymatters.com.au/renewab ... l-home.php

Good luck and let us all know how you get on.
Graham
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Re: How to best heat the SLAB ?

Postby Millsy » Wed Sep 30, 2009 12:12 am

Perhaps your best option would be a good quality wood fire, i dont knw where you are nor your access in your yard but if you can get wood delivered by the meter or by weight, then perhaps that would be your best option. even then buying a modern wood heater they are not cheap including the installation. running costs vary depending on the type of wood you can get. these heaters can also have a water jacket on the back to heat water linked to your hot water system then can be used also, perhaps it could be set to circulate water around your existing system.
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Re: How to best heat the SLAB ?

Postby andarm » Wed Sep 30, 2009 7:43 am

SOLAR - is there still an aversion to contemplating it. Would need to be a large system with huge storage but we need to remember to factor in on going running costs in a world where energy costs are going to radidly increase (and rightly so - they are totally unsustainable where they are). Large well insulated tank/s with appropriately sized collectors.
Have just done a heat loss calculation of our house now and with some modifications to see how much storage is required to tide us over during a "non solar period" i.e. night or cloudy day. I'm designing an air rather than water based system though as the storage and transport within the system is more complex with water. (A leak in an air based system can be fixed with a bit of duct tape!!!) Your distibution system is in place though so would make sense to at least do the numbers based on what's already there.
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Re: How to best heat the SLAB ?

Postby Millsy » Wed Sep 30, 2009 10:16 pm

its always worth looking at both options, see which best suits your needs. Regarding solar, i kind of think of it like, purchasing a car, your new car costs you quite a bit to start with, but it should cost you much less in running costs than your old one. Thats how i like to think about solar, it does cost quite a lot to start with but your on going costs of electricity will be dramatically reduced, and that way you also dont have to worry about the ever increasing costs as most of us do. and regarding solar electric hot water systems, you will find it saves you $5 per week. Doesnt sound much but when you consider its $60 a quarter off your electricity bill, and if your like me thats almost half my electricity bill gone. thats without solar pvs on the roof!!
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Re: How to best heat the SLAB ?

Postby moemoke » Thu Oct 01, 2009 12:37 pm

My parents had the same problem, so they used to go to Queensland for the winter, it was costing about $200 a week for heating with no town gas option available.
I dont think there are to many options that arnt going to cost a lot.
I wonder if you could replace the LPG boiler with a diesel one and run it on bio-diesel.
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Re: How to best heat the SLAB ?

Postby Millsy » Thu Oct 01, 2009 4:39 pm

hmm i don’t know about the conversion, would bio-diesel be cheaper than lpg? would a larger wood heater not be a better idea? we buy our wood from the sawmill off cuts, they sell it by the truck load, 5 cubic meters for about $220 i think. obviously you couldn’t get it from here, but do you not have a local saw mill that might do the same? you have to make sure its non treated wood though, otherwise it would be poisonous :S

$200 per week :S going to QLD would be a nice option, obviously thats not going to be compatible with work :(
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