Warmup Underfloor Heating vs Central Heating

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Beccara

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#954879 19-Dec-2013 14:42

We have had a multi room fujitsu heat pump system in our new house and it's amazing, We can turn on or off any room and it cools along with heating. We've see a pretty big decrease in our winter bills ($350-450 down to $180-240) and now it's summer we get a nice cool house aswell.

If i was in an area where it was always cold and you would never need colling in summer then gas might be an option however if you want to cool down in summer then heat pump all the way, ducted so you dont lose space.

Our 10kw unit covering 110m2 cost $7k installed and chills/warms the whole house in under 20 minutes

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timmmay

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#954880 19-Dec-2013 14:44

I have a 10kw unit in my lounge and a 7kw unit in my dining room. It works ok, but because heat doesn't go around corners well it's not perfect. 10kw should be enough for a new well insulated house, but 17kw is only just enough for an older house that's had a lot of insulation fitted but before anyone paid much attention to that sort of thing.

Those heating bills, did they go down in one house, or is that from a previous house?

langers1972

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#954882 19-Dec-2013 14:46

isis:
The other option which we're leaning towards is a gas central heating that can be ducted throughout the whole house at half the price. We have gas on the street.

Just bear in mind that ducted gas heating is forced air which can be a bit of an issue in terms of dust/allergies etc plus you've got to keep the filters reasonably clean none of which applies to radiators.

Just for info, we had gas fired radiators installed in our house and it ended up costing about $15k for 7 rads plus a condensing boiler and it's great

ajobbins

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#954928 19-Dec-2013 15:41

A relative of my ex-gf used to have the Warmup franchise in Wellington.

It costs a fortune to run. They had it in their own house and their power bill in winter was $600-1000 a month, for 3 people.

Sure it was nice and warm (and a nice kind of heat), but you better have deep pockets

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Beccara

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#955015 19-Dec-2013 18:54

timmmay: I have a 10kw unit in my lounge and a 7kw unit in my dining room. It works ok, but because heat doesn't go around corners well it's not perfect. 10kw should be enough for a new well insulated house, but 17kw is only just enough for an older house that's had a lot of insulation fitted but before anyone paid much attention to that sort of thing.

Those heating bills, did they go down in one house, or is that from a previous house?

One house built 1963, Only ceiling insulation. The power bill dropped from not using electric blankets and 2 x 2.4kw oil heaters. I think the company that sold it said 1kw per ~10m2 for old homes and 1kw for 25-30m2 for new homes when using a ducted system. They spent about 4 hours before we even purchased it testing flow in the house to make sure the outlets where in the best position

timmmay

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#955033 19-Dec-2013 19:13

Interesting to hear how much better new houses are. My house has heaps of ceiling, wall, and underfloor insulation, some double glazing, but it will never be as good as a new house. Might have to build a new house one day.

isis

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#955386 20-Dec-2013 11:06

timmmay: You can have heating ducts for the lower floor, you may just need to change the house design slightly. Alternately force the air down a central duct and have it come up through floor grates, though I doubt this is standard.

With lots of heat pump units you have lots of ugly outdoor units, and potentially long runs between the indoor and outdoor units. That's a bit less efficient I think. It also means lots of ugly high wall devices and lots of remotes. Even four heat pumps is going to be $12K. You could/should also put in a ventilation and heat transfer system which may let you warm some areas indirectly, though I doubt it would be as effective.

Remember with gas you have a per day charge for the life of the building. 50c/day for 50 years is $9K.

We're going to have a gas cooker and also a gas fireplace, much to my disapproval but it was one of the covenants of the property!
We're getting lumped with the gas cost regardless.
I've read articles which says that we can retrofit air-conditioning into these gas central heating devices. Not sure how good they are but apparently used widely in Oz.
If anyone on here that has had a good experience with ducted heat pump central heating installers, i'd be keen to hear/discuss this with them.

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mattwnz

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#955396 20-Dec-2013 11:19

timmmay: You can have heating ducts for the lower floor, you may just need to change the house design slightly. Alternately force the air down a central duct and have it come up through floor grates, though I doubt this is standard.

With lots of heat pump units you have lots of ugly outdoor units, and potentially long runs between the indoor and outdoor units. That's a bit less efficient I think. It also means lots of ugly high wall devices and lots of remotes. Even four heat pumps is going to be $12K. You could/should also put in a ventilation and heat transfer system which may let you warm some areas indirectly, though I doubt it would be as effective.

Remember with gas you have a per day charge for the life of the building. 50c/day for 50 years is $9K.

One thing with heat pumps is that they don't appear to have the longest life. I am not sure what their life expectancy is but I doubt it would come close to that of in slab water pipe heating. So over a long period of time they could cost a lot more to run with replacement costs.

mattwnz

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#955404 20-Dec-2013 11:26

SumnerBoy: Hey Isis,

I built a house 2 years ago and went down the route of installing underfloor hydronic heating. That is, pipes embedded in my concrete slab with an air-to-water heatpump running outside which warms up water to about 35C and circulates it through the slab - via a manifold.

As another poster mentioned, the manifold allows you to turn zones on/off and restrict flow (which in effect cools down that zone) however in my experience we find it best to just leave everything on 100% and let the whole slab warm up.

Someone else mentioned insulation and I wholeheartedly agree. Spend the money. It makes a world of difference, both in winter and in summer (when the interior of the house remains cool/comfortable on a very hot day).

My running costs for a 2-storey 260sqm house is about $180-190 a month in the middle of winter, with the underfloor running 9pm till 7am every day. The reason for these times is I am on the Day/Night rates from Genesis so electricity is only 11-12c/kWh during that time. And because I have a nice thick slab (200mm) I am able to 'charge' it up during the night when power is cheap, and it radiates warmth all day (I work from home) and into the evening before starting to warm up again after 9pm.

It is a fantastic system and I would be happy to share more details (I also have a temperature probe in the slab which stops heating too much in the spring/autumn months).

I tell anyone who will listen that hydronic underfloor is the way to go. It is a fantastic type of warmth, from the feet up, and being able to walk around on my polished concrete floors in bare feet all year round is a great feeling. Plus it is extremely efficient, but this again comes back to good insulation!

BTW - I am down in ChCh...

Just wondering why you had a 200 thick slab installed? Wouldn't that dramatically increase you build costs? I had heard that 100 is enough. Do you have good perimeter slab insulation and if so, how was this done on your house as it is something that is quite difficult to get right? What do you use in that house for cooling, and can you run cool water though it to cool down the slab?

timmmay

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#955418 20-Dec-2013 11:47

I have one five year old Daikin heat pump that's still working perfectly. I have it serviced every year or two, to be honest all they do is clean the filters, hose the outdoor unit, and sometimes do a chemical clean on the indoor unit. If the gas pressure goes down I think they may recharge it too.

SumnerBoy

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#955429 20-Dec-2013 11:54

mattwnz: Just wondering why you had a 200 thick slab installed? Wouldn't that dramatically increase you build costs? I had heard that 100 is enough. Do you have good perimeter slab insulation and if so, how was this done on your house as it is something that is quite difficult to get right? What do you use in that house for cooling, and can you run cool water though it to cool down the slab?

The idea of the thick slab was to increase the thermal mass. It is hard to measure but I think it makes a significant difference. In winter with the underfloor heating system running (9pm - 7am) the slab charges up during the night and has enough energy stored to radiate heat all day and into the evening, the house never drops below 20C even in the depths of our ChCh winters. And in summer the house never seems to over heat. It can get pretty warm after a couple of hot sunny days, but no where near as overheated as friends houses which are older and don't have the same insulation or thermal mass properties. I firmly believe the thick slab absorbs a lot of the summer sun/heat and 'dampens' the effect of the outside temperature fluctuations.

I went all out when trying to insulate the slab as well, after doing plenty of reading on Ecobob.co.nz and the like. I have high density 20mm poly around the slab perimeter which is wrapped in alu foil paper to try and reflect any heat loss back into the slab. There is 50mm poly under the slab (which is not as important as the edge stuff). I used 140mm framing so I could stuff one layer of 90mm ultra batts and then another layer of 50mm masonary batts to give extra thermal insulation.

I really wanted a better solution for my slab perimeter insulation but there wasn't anything available when I built (that I could find and that was going to get council sign off). Designers and builders are only just starting to realise the importance of this insulation, especially when you have in-slab heating. Hopefully this will improve and better techniques developed. Mine was very much a DIY approach but is hopefully better than nothing!

I don't find I need any cooling. I installed a floor mounted heat pump in the living room which is there for the shoulder months when the temp can drop but the underfloor hasn't been fired up yet. It can obviously be used for cooling as well. But I can honestly say in 2 years of living here I have turned on that heat pump 6-7 times for a heating boost, and never used or needed it for cooling.

graemeh

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#955439 20-Dec-2013 12:06

timmmay: I have one five year old Daikin heat pump that's still working perfectly. I have it serviced every year or two, to be honest all they do is clean the filters, hose the outdoor unit, and sometimes do a chemical clean on the indoor unit. If the gas pressure goes down I think they may recharge it too.

I asked a service guy once about if the gas needed to be checked or recharged.

He said the new ones operate at such pressure that any slight leak will lead to a complete loss of gas and the heat pump will stop working. So basically the gas is no problem until the pump breaks and then you need a repair done anyway :)

mattwnz

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#955464 20-Dec-2013 13:22

SumnerBoy:
mattwnz: Just wondering why you had a 200 thick slab installed? Wouldn't that dramatically increase you build costs? I had heard that 100 is enough. Do you have good perimeter slab insulation and if so, how was this done on your house as it is something that is quite difficult to get right? What do you use in that house for cooling, and can you run cool water though it to cool down the slab?

The idea of the thick slab was to increase the thermal mass. It is hard to measure but I think it makes a significant difference. In winter with the underfloor heating system running (9pm - 7am) the slab charges up during the night and has enough energy stored to radiate heat all day and into the evening, the house never drops below 20C even in the depths of our ChCh winters. And in summer the house never seems to over heat. It can get pretty warm after a couple of hot sunny days, but no where near as overheated as friends houses which are older and don't have the same insulation or thermal mass properties. I firmly believe the thick slab absorbs a lot of the summer sun/heat and 'dampens' the effect of the outside temperature fluctuations.

I went all out when trying to insulate the slab as well, after doing plenty of reading on Ecobob.co.nz and the like. I have high density 20mm poly around the slab perimeter which is wrapped in alu foil paper to try and reflect any heat loss back into the slab. There is 50mm poly under the slab (which is not as important as the edge stuff). I used 140mm framing so I could stuff one layer of 90mm ultra batts and then another layer of 50mm masonary batts to give extra thermal insulation.

I really wanted a better solution for my slab perimeter insulation but there wasn't anything available when I built (that I could find and that was going to get council sign off). Designers and builders are only just starting to realise the importance of this insulation, especially when you have in-slab heating. Hopefully this will improve and better techniques developed. Mine was very much a DIY approach but is hopefully better than nothing!

I don't find I need any cooling. I installed a floor mounted heat pump in the living room which is there for the shoulder months when the temp can drop but the underfloor hasn't been fired up yet. It can obviously be used for cooling as well. But I can honestly say in 2 years of living here I have turned on that heat pump 6-7 times for a heating boost, and never used or needed it for cooling.

Thanks, it sounds like your edge insulation is fine, so should perform well. I am building a new home at the design stage, and am certainly thinking about this sort of underfloor heating. The main problem I have is working out the best way to insulate the edges. Some of the houses I have seen have XPS, which is like polystyrene, but has better thermal properties for it's thickness and is also denser so doesn't compress. However becuase it is placed around the perimeter of the building, the flaming has to overhang the slab more, and the insulation then needs plastering over and waterproofing, and it is possible that it can be easily damaged from gardening around the footing. It could probably be protected more by fibre cement board, but I try to avoid that material.
The best solution so far I have found is one suggested by Branz, where you place a timber board between the concrete footing, and the floorslab, so the edge insulation layer is inside the building envelope, and you don't have any breaks due to footings needing direct contact with theground. The downsides of this are that timber isn't as good an insulation material as xps, and also you have steel ties between the footing and the slab which will penetrate the edge insulation, reducing it's effectiveness. I gues it could be done with XPS, but the timber gives something solid to nail into and walk on around the edge, eg if you want to install carpet, you need a string edge. I suppose if you have 140 framing, it could be hidden under the framing. The details I have been looking at are at http://www.designnavigator.co.nz/phpBB3/viewtopic.php?f=1&t=8 , and the branz one is the 3rd pic down, I am guessing your one is more similar to the 4th one down?

SumnerBoy

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#955478 20-Dec-2013 13:55

mattwnz:Thanks, it sounds like your edge insulation is fine, so should perform well. I am building a new home at the design stage, and am certainly thinking about this sort of underfloor heating. The main problem I have is working out the best way to insulate the edges. Some of the houses I have seen have XPS, which is like polystyrene, but has better thermal properties for it's thickness and is also denser so doesn't compress. However becuase it is placed around the perimeter of the building, the flaming has to overhang the slab more, and the insulation then needs plastering over and waterproofing, and it is possible that it can be easily damaged from gardening around the footing. It could probably be protected more by fibre cement board, but I try to avoid that material.
The best solution so far I have found is one suggested by Branz, where you place a timber board between the concrete footing, and the floorslab, so the edge insulation layer is inside the building envelope, and you don't have any breaks due to footings needing direct contact with theground. The downsides of this are that timber isn't as good an insulation material as xps, and also you have steel ties between the footing and the slab which will penetrate the edge insulation, reducing it's effectiveness. I gues it could be done with XPS, but the timber gives something solid to nail into and walk on around the edge, eg if you want to install carpet, you need a string edge. I suppose if you have 140 framing, it could be hidden under the framing. The details I have been looking at are at http://www.designnavigator.co.nz/phpBB3/viewtopic.php?f=1&t=8 , and the branz one is the 3rd pic down, I am guessing your one is more similar to the 4th one down?

Here is a picture of how my edge insulation looks;

As you can see the bottom plate hangs over the edge of the slab by 25mm. I wrapped the whole building in 7mm plywood as we were building in 2011 during all the fun and games of the earthquakes down here, so this extra bracing really helped. This also meant I could drop the ply down an extra 25mm below the bottom plate to provide something to hold the poly + foil in place during the build.

The exterior is clad with 50mm aerated concrete panels which were fixed to battons on the ply and the panels sat down on the footing. This was then all plastered so the poly is completely protected/hidden from the outside world.

Inside the footing below the slab I had 50mm poly up against the sides of the footing (as well as under), but where the slab sat 'on top' of the footings is where I needed this extra insulation.

Hope the picture explains what I am trying to say!

The solution you have found on BRANZ looks good though. As you say the only downside is that timber is a poor insulator, so it is debateable how effective it would be.

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