Underfloor heat pump heating

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timtait

133 posts

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#180997 28-Sep-2015 22:34

Does anyone have experience with one of these systems?

We're just about to kick off a new build in Dunedin and we've been looking into underfloor/in slab heat pump powered heating system, it's supposedly quite expensive up front but relatively cheap to run.

Alternatively we're looking at a ducted heat pump system.

Anyone have an opinion on either, or an alternative?

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#1396216 28-Sep-2015 23:22

Check those COP figures. As the colder it gets, the lower the COP and the lower the heat output. COP figures for when the outdoor temp is say 7deg would be pointless for you. What is the COP at say neg10deg? Also I would just recommend a ducted heatpump if you can put the outlets in the floor. As ceiling outlets can cause problems. If not possible the get wall mount heatpumps. Or just a woodburner. No point in getting gas where you are. Except maybe for cooking only.

Also any underfloor heating system will have poor response times. This will result in big temp swings if your house will get good sun (due to rapid changes in the amount of heat that the sun will provide).

And you will need to check your lines company connection policies. Since AFAIK they offer 30Amp connections in addition to 63A connections. And they will have policies around things like what things you can connect to night rate power. So you will probably want a 300L hot water cylinder so you can have it on night rate power. And if you end up getting a woodburner then you would want a wetback. And yes you can have mains pressure hot water with a wetback. A mains pressure shower is far better when the hot water is heated for free.

timtait

133 posts

Master Geek

#1396217 28-Sep-2015 23:25

I hadn't thought about the temp swings with the sun on the place, it get a lot of sun in the main living areas.

I haven't come across floor outlets for ducted heatpumps yet, I'll check that out cheers.

Aredwood

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#1396221 28-Sep-2015 23:55

Found it - the problems that a ducted heatpump with ceiling vents can cause. http://www.geekzone.co.nz/forums.asp?forumid=141&topicid=173759 Yet ceiling vents work good for aircon in open plan areas. But guess you won't be needing much aircon where you are.

mattwnz

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#1396226 29-Sep-2015 00:10

How are you planning on finishing the floors? Underfloor heating is best used under uncarpeted areas, as it is at it's most efficient when it is. If you put underlay and then carpet over it, it will act as an insulator, and won't heat as much. We were advised this when we were getting a underfloor system designed. You are best to have a concrete floor, eg sealed coloured concrete, or tiles. If you are down south, then I would think that you would benefit more from an underfloor system, as you will likely have it one most of the winter. You also may want to look at gas as teh heat source, if you are in a gas area, as I have heard it can be cheaper to run. Some power companies are now offering unlimited* gas plans. Although there is always an Astrix.

timtait

133 posts

Master Geek

#1396230 29-Sep-2015 00:28

Aredwood: Found it - the problems that a ducted heatpump with ceiling vents can cause. http://www.geekzone.co.nz/forums.asp?forumid=141&topicid=173759 Yet ceiling vents work good for aircon in open plan areas. But guess you won't be needing much aircon where you are.

Hmmm... that's some scary reading. Thanks for that

mattwnz: How are you planning on finishing the floors? Underfloor heating is best used under uncarpeted areas, as it is at it's most efficient when it is. If you put underlay and then carpet over it, it will act as an insulator, and won't heat as much. We were advised this when we were getting a underfloor system designed. You are best to have a concrete floor, eg sealed coloured concrete, or tiles. If you are down south, then I would think that you would benefit more from an underfloor system, as you will likely have it one most of the winter. You also may want to look at gas as teh heat source, if you are in a gas area, as I have heard it can be cheaper to run. Some power companies are now offering unlimited* gas plans. Although there is always an Astrix.

We're looking at a vinyl planking product for the open plan living area + the office, kitchen and scullery. The rest will be carpet. I had heard about carpet insulating the slabs but I'm struggling to find any figures on what level it affects it.

Gas is pretty much out of the question down here, we don't have access to natural gas so it's super expensive to run.

The only other reasonably priced central heating options would be diesel or coal powered boilers. Diesel is a lot more expensive than the coal option but the coal option requires a lot of maintenance, like every day maintenance. Not to mention they're both pretty dirty options.

jarledb

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#1396233 29-Sep-2015 01:51

Underfloor heating is brilliant though. I have not had experience with water based systems (which I am guessing you are looking at). But electric is pretty common in Norway (especially in bathrooms, can't believe the barbarity of it not being normal here in NZ).

Having the heat come up from underneath really makes a huge difference, and you don't need as much because it really helps that your feet are warm. In Norway its really common to use parquet as the top layer (which can be wood or vinyl).

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timtait

133 posts

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#1396235 29-Sep-2015 02:24

jarledb: Underfloor heating is brilliant though. I have not had experience with water based systems (which I am guessing you are looking at). But electric is pretty common in Norway (especially in bathrooms, can't believe the barbarity of it not being normal here in NZ).

Having the heat come up from underneath really makes a huge difference, and you don't need as much because it really helps that your feet are warm. In Norway its really common to use parquet as the top layer (which can be wood or vinyl).

Yeah it would be water based, you can even set it up so it's heating your hot water for the house too which is a bonus.

We lived in the UK for a couple of years and miss central heating so much, now that we have the opportunity to build it's fairly well up there on the priority list.

timmmay

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#1396399 29-Sep-2015 10:13

Under floor sounds good, far nicer than a breezy noisy heat pump, plus cutting holes in your ceiling for vents compromises your insulation. Putting them in the floor makes more sense. Good point about carpet insulating and keeping heat in - the concrete slab (if you have one) should be insulated if you're doing under floor heating. Talk to a UK builder/architect. Under floor heating is also slow to react, so if you have a hot or a cold day you can't really change your heating - solar gain is a factor.

You could just go with radiators, fed by a heat pump. You don't need air conditioning all that often in Dunedin.

davidcole

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#1396416 29-Sep-2015 10:25

Disappointed with my house....water heated radiators everywhere....and the previous owners implemented an electric based underfloor heater in a bathroom they remodelled....that an an electric towel warmer. The room even had a radiator in it already (ie piping to the room) which they cut off.

DOH. Maximise the use of the system if you're doing it.

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SumnerBoy

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#1396420 29-Sep-2015 10:27

I have hydronic underfloor heating (in ChCh) and it is fantastic. The key, as with any other type of heating IMO, is insulation. I don't think you can ever over-insulate. The more the better, you will be warmer in winter and cooler in summer. I also went for a thicker than normal slab (200mm instead of 100mm). The idea was to add more thermal mass and I think it makes a significant difference, although obviously hard to quantify. I only run my heat pump from 9pm - 7am each night (often less depending on the in-slab thermostat) and that is enough for 95% of the year. The slab warms up at night when power is super cheap (I am on day/night rates) and then releases the heat during the day. We have a floor mounted air-to-air heatpump in the living room that kicks in maybe 6-8 nights a year, in the depths of winter if we have 2-3 very cold days in a row - but the living never drops below 18-19 degrees regardless. In summer the extra thick slab seems to soak up any extra heat on sunny days and keeps the house very comfortable. Then in the evenings it radiates out and keeps everything very warm.

I really can't recommend it enough. Running only at night means our power bills never go above $250 a month, which I think is pretty good for a 265sqm house in ChCh. My home automation system tracks the living room temp and will fire up the air-to-air heatpump if the temp ever drops below 21.5 degrees - it hasn't run for a few months now.

The warmth is a lovely radiant heat, no air blowing around, and everything (furniture, joiner) is warmed up as well - I literally walk around in shorts and t-shirt all year round (I work from home).

But as I said, one of the key parts to this sort of system, is insulation. You really need to spend some time and money getting that right - otherwise you will spend excess power re-heating all the lost warmth. As timmay mentioned, a bit part of that is minimising thermal breaks in your insulation envelope - try and avoid downlights (unless under a second floor), try and get thermally broken joiner, and up-spec your batts as high as you can. I actually built my ground floor using 140mm framing so I could squeeze more batts in there (along with other reasons, earthquake related!).

Happy to answer any questions, I installed my underfloor system myself and just got a plummer to hook up the heat pump.

jonathan18

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#1396440 29-Sep-2015 10:51

timtait: We're looking at a vinyl planking product for the open plan living area + the office, kitchen and scullery. The rest will be carpet. I had heard about carpet insulating the slabs but I'm struggling to find any figures on what level it affects it.

My understanding is your carpet choice is relatively narrow, given you have to ensure both the carpet and underlay selected let the heat through. I believe some carpet and underlay is rated as such (wasn't this discussed in another thread not too long ago?). See sites like http://www.multipipe.co.uk/can-i-have-underfloor-heating-with-a-carpeted-floor-covering

SumnerBoy

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#1396481 29-Sep-2015 11:34

My old man put in underfloor and has oak flooring on top - still heats his house just fine. It might take a little longer for the initial *heatup* when you first switch it on in Autumn, but once running I am not convinced the flooring type will make much difference. Heat will always rise in preference to any other direction, so as long as you slab is well insulated (bottom and sides) the heat will eventually get into your house.

timmmay

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#1396524 29-Sep-2015 12:06

Heat doesn't rise, as such, warmer air is less dense and therefore "floats". Does heat in a solid have a preference to go up, down, or does it just radiate equally?

SumnerBoy

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#1396528 29-Sep-2015 12:09

I read some studies before building my place, where they measured where the heat *left* a concrete slab (sorry can't find it now but I think it might have been linked via the Ecobob forum). The upshot was that hardly any heat was lost thru the bottom of the slab, most of it went up and out the sides. Therefore the need for edge insulation of your slab is very important, more so than under-slab insulation. You obviously want as much going up thru the top as possible.

timtait

133 posts

Master Geek

#1396541 29-Sep-2015 12:18

SumnerBoy: I have hydronic underfloor heating (in ChCh) and it is fantastic. The key, as with any other type of heating IMO, is insulation. I don't think you can ever over-insulate. The more the better, you will be warmer in winter and cooler in summer. I also went for a thicker than normal slab (200mm instead of 100mm). The idea was to add more thermal mass and I think it makes a significant difference, although obviously hard to quantify. I only run my heat pump from 9pm - 7am each night (often less depending on the in-slab thermostat) and that is enough for 95% of the year. The slab warms up at night when power is super cheap (I am on day/night rates) and then releases the heat during the day. We have a floor mounted air-to-air heatpump in the living room that kicks in maybe 6-8 nights a year, in the depths of winter if we have 2-3 very cold days in a row - but the living never drops below 18-19 degrees regardless. In summer the extra thick slab seems to soak up any extra heat on sunny days and keeps the house very comfortable. Then in the evenings it radiates out and keeps everything very warm.

I really can't recommend it enough. Running only at night means our power bills never go above $250 a month, which I think is pretty good for a 265sqm house in ChCh. My home automation system tracks the living room temp and will fire up the air-to-air heatpump if the temp ever drops below 21.5 degrees - it hasn't run for a few months now.

The warmth is a lovely radiant heat, no air blowing around, and everything (furniture, joiner) is warmed up as well - I literally walk around in shorts and t-shirt all year round (I work from home).

But as I said, one of the key parts to this sort of system, is insulation. You really need to spend some time and money getting that right - otherwise you will spend excess power re-heating all the lost warmth. As timmay mentioned, a bit part of that is minimising thermal breaks in your insulation envelope - try and avoid downlights (unless under a second floor), try and get thermally broken joiner, and up-spec your batts as high as you can. I actually built my ground floor using 140mm framing so I could squeeze more batts in there (along with other reasons, earthquake related!).

Happy to answer any questions, I installed my underfloor system myself and just got a plummer to hook up the heat pump.

Hey thanks for that, I'll query the builder on going with a thicker slab.

Do you have it heating your hot water and do you have it run in your garage floor too?

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