Hydronic heating: in-slab vs panel hydronic heating (Gas boiler as base case)

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Hydronic heating: in-slab vs panel hydronic heating (Gas boiler as base case)

(18 posts) (7 voices)

Started 10 years ago by comfyhouse4me
Latest reply from ghostgum

Tags:

hydronic heating; gas boiler; in-slab; heat pump; runni

comfyhouse4me
Member

Hi all,

Firstly I'll say that I've read a lot of the discussion on solar boosted hydronic heating in this forum, but I'm hoping to put that topic aside for now.

I'd like to figure out the base case for the in-slab v.s panel hydronic heating.

Fun facts: Suburban Melbourne
My house will be two-storey, lightweight timber construction, waffle pod slab (with the obligatory edge insulation)- but of course that's only for the ground floor. I'm looking into hebel flooring but otherwise upstairs will be timber (with insulation between floors)
Ground floor (90m2)
First floor (50m2)

All living and bedrooms will be north-facing. Plenty of cross-ventilation, and if I have my way I'll have a thermal chimney arrangement above the stairs.
Stairwell and entrance will be zoned from other areas by extra doors.
Minimal east and west windows, with hardly any on the southern walls
Glass to floor area ratios are OK. Windows probably will be double glazed, timber frames.
I'll be maximising insulation, draught stoppers, curtains with pelmets at night.

I really do feel the cold, particularly my feet! I don't like ducted heating, much prefer radiant heat. I'm looking into in-slab heating but not sure what to do for the first floor.

At this stage I'm looking at exploring efficient gas boilers. I may consider an air source heat pump, however from what I've seen cost is an issue. I'll be borrowing for whatever system is put in, so paying interest on whatever the outlay is, so any reduction in running cost would need to cover outlay and interest.

I'm not nearly as tech savvy as a lot of you seem to be, so putting something together myself is not an option for me! However, putting that aside for the moment, at this stage I just need to make the decision of in-slab vs. panels.

* I understand that the water temperature for in-slab heating is much lower than that required for panels, but that there is a need to keep the heat constant within the slab? How does this balance out when it comes to running costs?

* I should add that placement of panels in the main living area may be tricky, especially on outer walls.

* Further, are there any options for having in-slab downstairs, panels upstairs, given the difference in water temperatures required?

* Given its lightweight timber construction, does anyone have thoughts of having underfloor heating upstairs in a screed over the hebel, and the extent of extra costs I'd incur to allow for the extra weight?

I currently work full-time, my son is at school, and so no-one is at home during the day except on weekends. That said, in a few years I may be working from home more. I have been told that in-slab heating is most beneficial if you're at home most of the day, but I'm not sure what to make of this.

I realise there are lots of questions in the above - I appreciate any advice you can offer.

Posted Sunday 27 May 2012 @ 2:38:04 am from IP #
ghostgum
Member

If you run hydronic radiator panels at 40C instead of 70C, then the heat output will be less than half. It will still work, but you will need to use a larger radiator.

Will you need heating upstairs, or will there be enough heat rising from the ground floor to heat the upper level?

You can do hydronic heating of wood floors, so you could do that for the upper floor. The PEX pipe is held against the underneath of the floor by aluminium head spreaders stapled under the floor. If you want to waste some heat but increase comfort, make sure there are more pipes under the bathroom floor than elsewhere on the floor.

If you insulate your place well enough (e.g. get to 8 stars), then a hydronic heating system is going to be expensive for the amount of use it gets. Most of the boilers assume much big system. I have a radiant panel hydronic heating system in my house. The standard gas boiler is a 34kW unit, but our's is wound back to 14kW since that is the heat dissipation of my radiator panels. For an 8 star house, you would only need 7kW and our gas boiler would be inappropriate.

Posted Monday 28 May 2012 @ 1:37:47 am from IP #
TonyT
Member

Threads that may be of interest are at

http://www.ata.org.au/forums/topic/3426
http://www.ata.org.au/forums/topic/3474

Posted Monday 28 May 2012 @ 2:40:29 am from IP #
karmacoma
Member

I put in hydronic heating with a mix of in-slab (downstairs north living area and front south-facing bedroom) and radiant panels (upstairs bedrooms). New energy efficient suburban house, my design and specs. Two bedrooms rooms face south because of how the block is oriented.

- The living area warms by passive solar during the day but eventually the heat leaks out so that by early morning it would be cold (starting in early May) without the extra heating. The thermostat has four time zones, so basically I've got it to turn on the hydronic furnace at 4:30 in the morning and keep it on until 7:00am (I'm still tweaking that). For the other time zones (daytime, nobody home), the thermostat temp is set low so that it would normally never signal the furnace to turn on. Great result, fantastically comfortable room.

- "However" Nr.1: the south facing downstairs front room (slab heated) won't get heated at all unless its manifold tap is full-on while the living-area manifold tap is turned almost off - i.e. to pump most heat into the bedroom slab. Even then the effect is weak: that bedroom doesn't really get much heat in that short amount of time. Only an issue because there's a lodger in there who sticks by herself, and also that one day that room might become a professional home office, so this inability to direct heat better throughout the day is a bit of a drag.

- "However" No.2: The panel heaters upstairs are totally useless. Thay were a waste of money. I think they work in Europe where I first saw them because they blast them on all day. But just turning on from 4:30am to 7:00am in the morning does nothing to heat those upstairs bedrooms via the panel heaters. Really you want the bedroom warm at 9pm-11pm at night when everyone gets into bed, then off (or low), then on early morning. That's not happening and it can't happen because the hydronic heat cycle is dictated by the living room's solar heating and thermal mass. I'm thinking seriously of taking the bedroom panel heaters to free up the wall space. If I took the thermostat out of the normally-warm living area and relocated it to the normally-cold front downstairs bedroom (I'm thinking about it), and then restrict the water flow into the living room slab while allowing full flow to that bedroom, it would probably even things up better. I don't know what effect that would have on the upstairs panel heaters: maybe I'd get the heating cycle for them to work when needed.

So see what I'm saying: slab heating and panel heating want quite different thermostat regimes (mass system vs no-mass), and deciding the placement of thermostat within hot and cold zones of the house is important. Don't know why the company who installed the system never mentioned those factors or discussed them with me prior to the job. Maybe they don't know those sorts of things. I didn't research far enough into it either.

I agree with the previous post that size of boiler is an issue: the company that sized mine I went for way too huge (Sime 34E - a roaring beast of a thing) because they are accustomed to jobs on shittily-built leaky poorly insulated houses I think.

Posted Monday 28 May 2012 @ 3:12:08 am from IP #
TonyT
Member

karmacoma

Before you make any changes, it may be a good investment to find a person who understands hydronic heating and employ them to assess your system and to recommend how best to make it work for you.

Posted Monday 28 May 2012 @ 3:55:33 am from IP #
karmacoma
Member

Employ someone? Man, after that house build I've got the biggest mortgage. If I don't figure it out myself (with a bit of help from www), it won't happen. But I'll admit that's a poor attitude - you know, like, I should freak out, panic, cry 'I can't do this', and call an expert.

Anyway, main point is, as I see it, to watch those two factors: mixing in-slab with radiant panels, and optimising thermostat control between solar-heated and non-solar heated zones of the house. Given that your only levers are positioning of the thermostat and the flow settings on the distribution manifold. But, what do those who actually understand stuff have to say.

Posted Monday 28 May 2012 @ 8:14:59 am from IP #
sun2steam
Member

There are more levers. You can use thermostatic mixing valves in the individual heating loops to adjust the heating temperature.

In addition you should have thermostat valves with the radiators.

In addition I recommend that you are more polite. It was not nice how you replied to TonyT.

Posted Monday 28 May 2012 @ 8:19:23 am from IP #
Jeffbloggs
Member

Karmainacoma
On a forum the cost of information is that of courtesy and common decency. I too would recommend seeking professional help. For your system of course.

Alternatively please post a circuit diagram of your hydronic system so that we too can become experts at how it doesn't work. It is hard to decipher the connections between your "lodger", thermal mass, solar input and heat loss.

At a minimum you will require individual thermostat valves on your radiators as S2S suggests.
Regards
JB

Posted Monday 28 May 2012 @ 8:37:19 am from IP #
comfyhouse4me
Member

Thank you all for your responses.

I've come down with an awful cold and can't think through the fog! When I snap out of it, I may have more questions! I'll look at the other threads then as well.

Posted Monday 28 May 2012 @ 8:44:42 am from IP #
karmacoma
Member

Sorry not to be more polite. I noted down the information above on how my system behaves, so as to be a cautionary tale for others. The company who did the installation are the biggest supplier/installer in this part of the country and very long established (no further clues, sorry). They did the design, they didn't get it right, but they were the professionals. You are better to learn for yourself. The only things in my new place that didn't work out were the bits that I didn't pursue vigourously enough to question closely, specify exactly and supervise diligently. Trust of professionals is not sufficient for a good outcome. You have to know the stuff yourself. Certainly ask lots of questions but if you can avoid it don't rely on others whoever they say they are. That's my experience, guess I'm not gonna get a lot of love for that. Incidentally I won't be doing any remediation to my system this season, so am not casting for OT advice myself. I'll keep in mind the thermostatic mixing valves though, ta.

Posted Monday 28 May 2012 @ 12:09:56 pm from IP #
TonyT
Member

karmacoma

I suspect that a person who understands hydronics could assess your system and make suggestions in less than 4 hrs - hopefully much less.
Even if they charged $150/hr you would be way in front compared with what you said above about pulling out radiators and starting again without first fully understanding why the present layout is not performing.

The fix may be extremely simple.

It should be possible this winter to get some benefit from what you have already spent.

The key is to select the right person !

People on this forum may be willing to share their experiences with hydronics experts who service Canberra.

Fitting a $30 thermostat valve on each wall-radiator would be a good starting point.

I found that setting the correct opening for the lockshield valve on each of my radiators was tricky and that it was not understood by any of the local "experts" from whom I sought advice. After I worked out how to do it, I found three local (SA) plumbers who seem to know what they are talking about.

If you read the posts about hydronics on this forum you will find people who have the knowledge and the experience to help you.

Posted Monday 28 May 2012 @ 9:17:33 pm from IP #
karmacoma
Member

Thanks Tony, I came across a little of your recent experiences just then on a quick search on lockshield valves. It's clearly an involved field of knowledge, one I'll have to get on to at a later stage, to ensure I have a good basis for discussing it further.

Yes I am in Canberra. The building industry here is at full employment, a great danger of that is insufficient care by contractors. Of all my contractors only one had real pride, intelligence and care in his work and that was Helmreich the cabinetmaker from Bemboka. I trusted the hydronic people based on their reputation, I now see I should have known my stuff before I made any decision on system specs - I should not have left it up to them to just 'quote', without the informed, close questioning approach I used on other aspects of the building. But then as now, it is not something I felt drawn to wanting to know a lot about. I will have to learn up on it though before getting anyone else over to look at it with me.

I'd say to anyone considering hydronic heating that the risk of being dudded seems high with this kind of system as it is a complex design problem, one that is not in the interests of the contractor (no matter how established, large and reputable) to work through before they just start whacking stuff in as fast as possible before moving to the next job. Your only defence is to become very, very informed on this particular branch of HVAC engineering. It's potentially the best heating system (other than pure solar, of course) but seems to be the most difficult to get right.

But yeah, on mine, when I get through other things a bit I suspect should be possible to remediate it, and would welcome advice from this forum when that time comes. Once I feel I have a strong grasp of it myself I'll seek out and pay someone for specific known inputs if I decide that I need to.

Posted Monday 28 May 2012 @ 10:44:02 pm from IP #
ghostgum
Member

As a counter to karmacoma's experience, I have found the only problem with my hydronic system was the oversized boiler, which required a visit by their most experienced person to adjust the boiler settings. The installer didn't think I needed the thermostatic valves. Turns out he picked good locations for each radiator (new build), and sized them correctly for every room bar one. Consequently the thermostatic valves can be pretty much set to full on (28C) and the electronic thermostat in the main room sets the temperature. The only thing you can do with a thermostatic valve is set the room temperature lower than the main thermostat. The room with the wrong sized radiator is the bathroom - it was sized for the room, but it really needed to be sized for the room plus basin and passage areas outside. I've found that it takes twice as long to heat the house as a gas ducted air heater.

We have wooden floor boards, so a cold floor isn't an issue except for the bathroom which has tiles over a compressed fibro cement sheeting. Instead of a radiator in the bathroom, I wonder if we could have used underfloor heating using the return water from one of the radiator panels (to get closer to 40C water).

Posted Tuesday 29 May 2012 @ 12:00:03 am from IP #
karmacoma
Member

Wait, before this thread goes completely stale, I want to make a comment and ask a question.
- Ghostgum's positive experience of a hydronic system seems to relate to a house in which all the hydronic heat is delivered to all the rooms by radiant panels. The finesse is to balance the heat from each, but in a situation that does not have unbalanced thermal inertia in the system. By which I mean, the problems I outlined about my house are I think basically attributable to the attempt to use a hydronic system that in one area of the house works to supplement heat to a slab already warmed by the sun (the slab has thermal inertia), while at the same time attempts to deliver heat to rooms that do not have the sun-heated slab. The further complication in my case is that one of these 'cold' areas (i.e. no sun-heated slab) is a south facing room on the heated slab that wants to soak up heat with a slow response, while two further 'cold' areas are upstairs in lightweight rooms, serviced by radiant panel heaters that react rapidly but have practically no thermal inertia. That's the mix of different characteristics that seems to be diabolical and should have been anticipated and designed for at the start by the hydronic heating company installers.

- The question I have, I suppose at some risk of being called a mental case again, is whether anyone has seen or heard of the possibility of equipping the heating manifold (the set of hydronic taps poking out of the slab inside the laundry cupboard) with individual thermostatic flow control on each tap (or at least some of them), where the thermostat signals are fed from room sensors for each. This would be to control the slab heating better vis-a-vis hot parts of the slab and cold parts of the slab, and also in relation to the panel heaters. I could imagine that with that facility, especially if the thermostats also could be set to respond differently at different times of the day, it would be possible to master the system and control it at will. But is anything like that ever done or not?

Posted Thursday 31 May 2012 @ 11:05:59 pm from IP #
ghostgum
Member

karmacoma, yes you have summarised my system well. We have low thermal mass inside the house, and the hydronic system heats the house evenly.

You may not be able to use thermostatic valves if the manifold is in a different area to the area you want to control You should be able to use active valves with a remote electronic thermostat to achieve what you want. You need to make sure that not all areas can be turned off, so the boiler can always push water around when it is running. I expect that your main thermostat needs to be in the area that requires the most heating and is always on (e.g. your south slab), and then the areas requiring less heat have the ability to turn off heating (e.g. thermostatic valves on panel radiators upstairs, and remote valve for the northern warm part of the slab). You may still have problems if the slab downstairs is warm and hence the upstairs radiators get no heat, but at least in that situation there should be some heat rising through the building to keep the upstairs warm.

In my case, the main room containing the electronic thermostat does not have thermostatic valves. The valves on those two panel radiators are always open. The other 8 radiators have thermostatic valves, and I could have saved $50 per valve by not installing 5 of them.

Posted Thursday 31 May 2012 @ 11:40:54 pm from IP #
karmacoma
Member

Ghostgum, that's shaping up to look like a possible solution to my situation. This thread has got my mind ticking over.

Posted Friday 1 Jun 2012 @ 8:16:24 am from IP #
chazwah
Member

hi,
i have read through all post's for this topic and there seems to be some people who know there stuff.I am building in the south subs melbourne around Rosebud ,can anyone point me to a hydronic specialist who knows there stuff.I am owner building and really want to get right.Help appreciated

Posted Sunday 17 Jun 2012 @ 11:33:27 am from IP #
ghostgum
Member

My hydronic system using radiator panels was installed by Nissl Eichert Heating.

Posted Sunday 17 Jun 2012 @ 11:44:46 am from IP #

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