Hydronic heating

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blackjack17

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#249129 26-Apr-2019 21:11

Hi all

Looking at building in Auckland in the next year and we are interested in the option of hydronic heating (heated water pipes through the slab).

Has any one put one in? If so do you mind sharing details? What make and model, up front cost, running cost, gas or heat pump? Any issues?

As far as I can tell cost is similar to installing heat pumps and with my experience with underfloor heating in Korea, the heating experience is much more pleasant.

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Aredwood

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#2225879 26-Apr-2019 22:10

As a Plumber / Gasfitter. Definitely consider ducted heatpumps or individual heatpumps in each room instead. As hydronic heating is slow to respond to changes in the heating load. Things like the sun coming up / going down etc. And Auckland gets hot enough during summer, that I consider air conditioning to be an essential.

Hydronic heating works far better in countries where winter is freezing cold for weeks on end (lots of European countries). Unsure if the winter weather in Korea is also like that.

I have been called in to fix poorly designed systems. Worse one was a house that had an open plan kitchen / lounge / dining room. That had lots of very large windows, and which also got lots of sun through those windows. In winter, the boiler had to work hard and get the floor slab nice and warm, to deliver enough heat to keep that open plan room warm despite all of the windows. Then the sun comes up, and due to those windows, can easily deliver enough heat to keep the room warm without any additional heating (even in winter). Except that the floor slab is still hot, and still delivering lots of heat to the room. Room quickly gets stinking hot, and owners are forced to open the windows, and dump the heat that they have already paid for. Then when the sun goes down, room would quickly get freezing cold. As the heating was off all day, the slab had since cooled down. And it now had to reheat before the room could start to warm up.

Those people had to give up on the system and just get highwall heatpumps instead.

If I was building a brand new house. I would still install hydronic heating. But I would design the system to only heat the floor slab to no hotter than my target room temperature. (maybe 1 or 2deg less than target room temp) And I would then install individual heatpumps in each room. And some home automation logic to control the heatpumps and hydronic system together. The idea being that the floor slab thermal mass would buffer the rooms against rapid temp drops. You have excellent control over the temp of each room. The heatpumps can be undersized, (compared to a heatpump only system) as the hydronic system will help them in the depths of winter.

Hydronic system + heatpumps would only be used during winter. With the heatpumps by themselves would be used during the other seasons.

Note that there is no regulations around who can work on hydronic and radiator central heating systems in NZ. So beware of cowboys. Although plumbers typically do such work. Since those heating pipes don't carry drinking water, and they are not drain pipes. They don't come under the rules that regulate plumbers.

Heat sources - If gas, only use Natural gas. As LPG is both too expensive. And NZ LPG is a mixture of Propane and Butane. The high efficiency European boilers often can't handle that variable mixture that is NZ LPG. As for heatpumps, Direct air to air heatpumps would likely be more efficient than the air to water heatpumps used for hydronic systems. But still consider them.

Also in relation to gas - get a proper dedicated central heating boiler, and check it's efficiency rating. As often a gas hot water heater will be bodged to run the hydronic. And it then ends up being really inefficient, as it is not being used for what it is designed for. And such water heaters typically need really cold incoming water to be able to operate at peak efficiency. And if using gas for both heating and hot water. Just use separate systems. A combined system is unlikely to be cheaper in NZ.

mattwnz

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#2225974 27-Apr-2019 01:32

I looked into this system but decided against it for many reasons, but the main one was response times. I believe they do work well down south where you really need the heat. Instead am using a large room heatpump and multi unit heatpumps around the house, as well as wood burners. The big benefit of heatpumps is cooling,which you don't get with underfloor heating. Also we were told that they need to be maintained and have to clean the tubes every year or two with a special liquid they pump through the pipes. Also have put normal underfloor heating under tiles in bathroom, so the floor in those rooms is warm.

Also if building, the risk of a hole getting drilled through a pipe, or a leak occurring is potentially quite high. eg the builder installs doorstops and drills straight through a pipe.

One big issue I found when looking for info on underfloor heating systems, was the lack of independent and impartial information. All these companies that sell them are trying to sell their own systems, so the consumer really doesn't know which is the best one to go with.

Sidestep

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#2226020 27-Apr-2019 05:22

I agree with everything @Aredwood says above, there are likely better options for full house heating in NZ.
I do think hydronic heating has a place - where it really shines are bathroom, laundry, kitchen & mudrooms. Anywhere that has tiled floors, few windows and/or is damp.

I'm no plumber - so take everything I say with a grain of salt..
I've designed and built a few of my own systems – mainly on the Canadian Prairies, and in the Rockies where the climate is perfect for them, and one quirky one in NZ.
My Dad spent a couple of winters in Korea during the 50's and from his description winter there is very similar to Canada.

I've found the type and size of the boiler and correct zone design are very important.

The NZ one was unusual. An off grid house, using a Marshall (made in Tauranga) wood boiler – with their fire-door mounted diesel backup burner - as a hot water feed, a hybrid underfloor and wall mounted, fan forced radiator system.
Underfloor heating for bathrooms, bedrooms and garage (all on the shaded side of the house) 'Myson' – combo fan-forced/radiant wall mounted heaters – with individual thermostats - for the sun heated rooms of the house. In that situation wood was cheap/free, her solar generated electricity at a premium.

The Canadian ones had dedicated gas boilers (natural gas here is relatively cheap).

One system in our business premises was again a combo, underfloor zones of orange pex-al-pex with glycol (in case of freezing) in the slab of a 1500 ft2 shop, and between the joists of the 1,000 ft2 upstairs office, large fan forced radiators heating a 60' x 40' high stud workshop. The whole thing ran easily from a 180,000 btu boiler through -30C weather.

One house we had – the same issue described above - two rooms with large, sun facing windows.
We ran roughly concentric zoning in those rooms. In sunny weather we'd have just the 'outside' zones running heat around the edge of the slab near the external walls, under the windows and doors.
We'd progressively heat more zones in cloudy or very cold weather. Because of the 'lag' in floor heating & cooling times we had to be a bit proactive and watch the weather forecast, remote control of the thermostats was useful.

blackjack17

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#2226026 27-Apr-2019 08:27

We are not interested in cooling. We have a heat pump in our current house and have never used it as an air con. We also have a fireplace and truth be told we use the heat pump half a dozen times a year.

I can see how it could make a house to warm on winter afternoons. Esp if it was run with a heat pump water heater and solar panels and you had massive solar gains.

Big solar gains won't be an issue on this site as the down stairs would be shaded by neighboring houses. Upstairs will get all day sun.

I was hoping with a balanced heat exchanger ventilation system it could be the sole heating source. With maybe a fireplace for ambience.

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Jase2985

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#2226164 27-Apr-2019 10:35

you also need to make sure you insulate the slab and its edges to ensure you keep the heat in your slab.

i considered it but dismissed it for Auckland, it doesnt get cold enough here for it. was just going to go with balanced pressure heat recovery with heat pump/s. + polished concrete floors for thermal mass

bfginger

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#2252728 6-Jun-2019 06:53

Unless the house is shaded a house built in Auckland shouldn't need central heating. The standard build in New Zealand has very poor thermal design values which gives the wrong impressions. The money dropped into a central heating system could go into making the house be built closer to modern standards so it doesn't need much if any heating. In your case a good multistorey ventilation system should help even out temperatures but they're rare in New Zealand.

If the slab is going to be warmed it should have good slab edge insulation. Overseas they may install hydronic heating over the slab instead of in it.

We are not interested in cooling.

If this is a standard New Zealand build to quote Yoda "you will be". Overheating is either ignored or dealt with clumsily in the typical contemporary New Zealand house design.

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Disrespective

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#2253861 7-Jun-2019 14:21

I've worked on multiple residential projects where hydronic was asked for, by the client, and then leaked causing MASSIVE issues whereby they are no longer in service. I would avoid them above all other options for in slab heating.

If you really truly don't care about cooling in Auckland then you either come from a significantly hotter climate than here, or plan to build a VERY good passive house with great insulation, designed passive ventilation paths, and little to no north glazing. If this is the case then good on you, we need some more passive housing and would love to see what you come up with. If not then I would be very cautious.