Underfloor heating options for new build in Hikuai, Coromandel

Forums › Home Workshop DIY › Underfloor heating options for new build in Hikuai, Coromandel

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mattwnz

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#1745915 22-Mar-2017 15:55

nofam:

mattwnz:

k1w1k1d:

My understanding is that underfloor heating is better suited for northern hemisphere areas where it is freezing cold for days or months on end.

Or Invercargill/ Dunedin area :) I spent a long time determining whether it was worth it for a new build I am working on at the moment. The cost to install was going to work out at about 60k with a totally automated system off water heating heatpumps. Instead decided to go with a multiunit heat pump running off a large single compressor, so you don't get ugly boxes all round the house. Also going for wood burners as well. This means you get heat when you want it without having to plan. Also get cooling for summer. It was also supposedly going to cost over $20 per day to run the underfloor heating system. Then there were also maintenance charges for flashing out the tubes etc. But I would look at underfloor heating if I was to do a small house, and was doing alot of the install myself. It just didn't work out on a large house.

What part of Otago/Southland are you in @mattwnz? About to build in Mosgiel, and a Hydronic UFH system is less than $20k (including the heating of all domestic HW).

Mine was in the wellington region but was estimated 60k +. But we rarely have winter days that are cold 24 hours of the day with no sun, and on sunny days, can use passive solar gains with large glass windows/doors to heat the tiled slab.

EmmaOffshore

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#1745950 22-Mar-2017 16:36

Thanks everyone for your input and thoughts.

Talked to neighbours at our property and they reckon its cold approx 2 months of the year. UFH may be over kill but also we may decide we want it. Snow is not unheard of (which was news to us). So we're going to go with putting pipes only in the slab and enough space to run a system if needed. To be honest running costs of $20+ a day do put us off somewhat.

SumnerBoy

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#1745957 22-Mar-2017 16:55

I run this system in ChCh using a 9kW heat pump, to heat a 260sqm two storey house. I have a very thick concrete slab (300mm) to increase my thermal mass, and I went overboard on insulation with 140mm framing and high-spec batts. I find I only need to run the underfloor from 9pm till 7am, even in the depths of winter. This keeps the house at 20 degrees no problem all day (I work from home). And because I am only running the system at those times I only have to pay 15c/kWh instead of 34c during the day.

This means the daily running cost is very low. The heat pump usually sits there ticking along drawing 3kW so even if it is running for the full 10 hours over night, it only costs $4.5. And it is only working that hard for about a month in the middle of winter. The rest of the time, during the shoulder months, it is only running from between 4-6 hours a night.

A lovely warm house, not too expensive, and no air being blown around the place. We absolutely love the system, but the key is properly insulating and ensuring you are not bleeding the heat you are generating.

nofam

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#1746012 22-Mar-2017 19:10

SumnerBoy:

I run this system in ChCh using a 9kW heat pump, to heat a 260sqm two storey house. I have a very thick concrete slab (300mm) to increase my thermal mass, and I went overboard on insulation with 140mm framing and high-spec batts. I find I only need to run the underfloor from 9pm till 7am, even in the depths of winter. This keeps the house at 20 degrees no problem all day (I work from home). And because I am only running the system at those times I only have to pay 15c/kWh instead of 34c during the day.

This means the daily running cost is very low. The heat pump usually sits there ticking along drawing 3kW so even if it is running for the full 10 hours over night, it only costs $4.5. And it is only working that hard for about a month in the middle of winter. The rest of the time, during the shoulder months, it is only running from between 4-6 hours a night.

A lovely warm house, not too expensive, and no air being blown around the place. We absolutely love the system, but the key is properly insulating and ensuring you are not bleeding the heat you are generating.

Excellent post as always @SumnerBoy - the other thing to remember about hydronic UFH systems is the whole floor becomes a radiant heater, so you can actually have them at a lower temp than you would for (say) a heat pump. Also, as mentioned above, heatpumps are convective heating, so by definition move air around creating drafts. If you're going to go down this path, spend your money on creating a thermal envelope that will retain the heat, especially around the edge of your slab, as this is where most heatloss occurs (not down through the bottom of the slab).

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