# Which Heating System???



## NoIdentity (28 Apr 2009)

I am building a new house and need to decide on a heating system. I am sure that I want underfloor heating but am confused about which heating system to use.

Excavation has begun on the site and the earth movers are telling me that I need to decide on the heating system immediately as it will determine the depths of the floors. 

I was considering 3 options: oil based condenser boiler, geo-thermal and air-to-vent.  I have an extremely tight budget which seems to rule out the latter two (quotes for those coming in around €20K).

Does anybody have any advice??


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## galwaytt (28 Apr 2009)

I think you're a bit confused there, or possibly the builder is !! :

You're asking a different question from what the builder is asking you !

What you're asking is what sort of heat source you use, the heat 'generator' if you will........that has nothing to do with floor levels.

The question you're being asked _*on site*_ about floor heights is based on what type of heat DELIVERY mechanism you're using, e.g. rads, ufh, vent/ducts. This is because they need to know about how much insulation and floor screed they will be putting in, over the foundations. My personal advice for UFH would be to use no less than 100mm insulation under a 65mm screed. If you can, use 150mm. Layed in 50mm layers, in both cases, with joints staggered.

On a 20k budget, I don't think Geo is at the races. You're more than covered on an oil boiler. For an aerothermal system.........mmm, that, sorry I'm not sure of.   What size, and what's the house made of (that might help you decide) ?


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## NoIdentity (28 Apr 2009)

Thanks for your reply galwaytt.

I guess the on site question was directly about the heat delivery mechanism but I was under the impression that the delivery mechanism will be determined by the source. Or are they completely independent of each other?

I know that I don't want rads and would prefer underfloor. The 100mm and 65mm screed sounds good. Is the expense of going 150mm justified in heat savings?

The house will be built most likely from blocks (although I am getting tenders for timber frame and Amvic/ICF).


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## NoIdentity (28 Apr 2009)

I have been thinking about a polished concrete floor.  Is that kind of floor suitable to underfloor heating?  Is it likely to crack?


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## baldyman27 (28 Apr 2009)

Check out the regs re: depth of insulation to be used for UF.I have a feeling that changed last year to 125mm min. If you are thinking of geo-thermal, then this *could *affect the level of the foundation as quite a large duct is required to pull the pipes. A plumber on a recent job I did insisted on a 12" duct, though if your rising walls are the standard minimum, this would suffice. Keep your screed to 75 - 85 mm as anything over this decreases efficiency AFAIK.

A 'polished' concrete floor - do you mean a power-floated finish? If so, then this is perfectly suitable to UF. It's quite hard to guard against cracking, but most often these are small, hairline cracks that are of no consequence. The screed is not a structural element.


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## wexford dude (28 Apr 2009)

NoIdentity,

Don't let yourself be put under pressure.I assume you are going direct labour.You are going to have to stand up to sub-contractors and not be bullied.What has the groundworker priced - is he taking the house up to ground floor level or is he preparing the site and pouring the foundations.
If he is not doing the rising the blockwork then this gives you time to decide what you are doing - although in fairness you should have all this organised before you start.
If you are going for ufh then the norm is to pour a protective slab on top of your radon membrane with the top of this slab 225mm (1 block on edge) below ground floor level.This leaves a build up of 150mm insulation & 75mm screed.The norm is that after the house is built the insulation is laid and the screed poured.I have never understood why people don't just place the hardcore,lay their radon, lay the insulation, place their ufh heating pipes and then pour the screed.At this stage you have the room layout on the ground floor and its so much easier to pour the ground floor screed before the house is built.You will need to leave an opening in the external wall for the flow & return pipe from your heat source - oil, geo, etc.
The other option is to have rads which means that that your screed is poured to ground floor level with your heating pipes in the screed for your rads.My preference is to use 4''x3'' to box out the runs for the pipes from the hot press.This means that the pipes will be laid when the house is finished and any problems detected and solved.
The other alternative is to use a HVAC system which sends heated air through a MHRV system.
You need to have a good look at the heating system and what way you are going to insulate the house.Personally I would spend more on the insulation and keep the heating system simple.
Also you need to check what you are doing as regards waste pipes from your bathrooms.If they don't go in underneath the radon they will have to go above ground through your external walls.


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## NoIdentity (28 Apr 2009)

I'm looking at ground & polished floor finishes like these: [broken link removed]


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## NoIdentity (28 Apr 2009)

Thanks for the encouragement Wexford dude. You are correct, I am going direct labour.  Right now the earth mover is carrying out the bulk excavation.  He wants to quote me to dig and pour the founds and bring it up to the floor slab.  So I guess the discussion I'm having with him now is planning for the next stage.


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## baldyman27 (28 Apr 2009)

wexford dude said:


> The norm is that after the house is built the insulation is laid and the screed poured.


 
This has never been the norm on any jobs that I've done. We bring the floor to FFL before the blocklayers come in.

Wexford Dude, you're right, the OP should have their mind made up at this stage. However, to suggest that he/she is being bullied by the subbie is a bit unfair. Especially when you consider that the subbie is quite possibly working at, or very near to cost. Every hour lost, not to mind days, pushes the subbie closer, or into, losing money on the job. Prices are great for clients these days, but be some bit fair to the subbie involved.


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## baldyman27 (28 Apr 2009)

NoIdentity said:


> I'm looking at ground & polished floor finishes like these: [broken link removed]


 
Couldn't see any problem with using this with UF, however, best to check with them. What I would suggest is that your finished floor is poured to within very strict level tolerances and that you have something in writing with the contractor re this. Make him aware that this is the finished floor.If he doesn't have the equipment or expertise to pour to these tolerances, it is in neither of your interests to let him do it.


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## NoIdentity (28 Apr 2009)

> Especially when you consider that the subbie is quite possibly working at, or very near to cost.



This is true. The subbie is pretty sound and is working to keep his machinery and men in work. He is a local guy and I feel that I can trust him. He just wants to know how far to build the floor up to.

Do you think it would be wise to let the subbie do the floor up to the 225mm gap, then let the UFH people take it from there?


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## baldyman27 (28 Apr 2009)

If the groundworks subbie is reputable and experienced in doing the whole base, let him do it. We do bases up to the finished screed. All you need to do is appoint your plumber and let the subbie deal with him then. He'll liaise with the plumber as to when he'll come in to install the waste pipes, etc., then the groundworks guy will bring it up to and including the insulation before calling in the plumber to install the UF. Groundworks guy then pours the screed.


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## galwaytt (28 Apr 2009)

baldyman27 said:


> Check out the regs re: depth of insulation to be used for UF.I have a feeling that changed last year to 125mm min. If you are thinking of geo-thermal, then this *could *affect the level of the foundation as quite a large duct is required to pull the pipes. A plumber on a recent job I did insisted on a 12" duct, though if your rising walls are the standard minimum, this would suffice. Keep your screed to 75 - 85 mm as anything over this decreases efficiency AFAIK.


 


wexford dude said:


> - is he taking the house up to ground floor level or is he preparing the site and pouring the foundations.
> If he is not doing the rising the blockwork then this gives you time to decide what you are doing - although in fairness you should have all this organised before you start.
> If you are going for ufh then the norm is to pour a protective slab on top of your radon membrane with the top of this slab 225mm (1 block on edge) below ground floor level.This leaves a build up of 150mm insulation & 75mm screed. The norm is that after the house is built the insulation is laid and the screed poured.I have never understood why people don't just place the hardcore,lay their radon, lay the insulation, place their ufh heating pipes and then pour the screed.At this stage you have the room layout on the ground floor and its so much easier to pour the ground floor screed before the house is built.You will need to leave an opening in the external wall for the flow & return pipe from your heat source - oil, geo, etc.
> The other option is to have rads which means that that your screed is poured to ground floor level with your heating pipes in the screed for your rads.My preference is to use 4''x3'' to box out the runs for the pipes from the hot press.This means that the pipes will be laid when the house is finished and any problems detected and solved.
> The other alternative is to use a HVAC system which sends heated air through a MHRV system.


 


NoIdentity said:


> He wants to quote me to dig and pour the founds and bring it up to the floor slab. So I guess the discussion I'm having with him now is planning for the next stage.


 
Sorry, something needs to be clarified here: are you not pouring a raft/slab foundation ? Or are you pouring strip foundations ?

Tbh, a raft is easier and more accurate, to work with.

------- Declared interest: we build SIP houses on rafts all the time ----

Have a look at one of our standard details, as an example:


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## baldyman27 (28 Apr 2009)

galwaytt said:


> Tbh, a raft is easier and more accurate, to work with.


 
As well as being more expensive and totally unnecessary unless ground conditions dictate otherwise. Why would they be more accurate?


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## galwaytt (28 Apr 2009)

baldyman27 said:


> A plumber on a recent job I did insisted on a 12" duct, though if your rising walls are the standard minimum, this would suffice. Keep your screed to 75 - 85 mm as anything over this decreases efficiency AFAIK.


   The size of the duct is immaterial - you can put it right under everything.  Zero-loss pipe, and it's assoctiated duct is so stiff, and needs such a big radius to bend it, you're better off going way, way down, and coming through the floor, square.



> A 'polished' concrete floor - do you mean a power-floated finish? If so, then this is perfectly suitable to UF. It's quite hard to guard against cracking, but most often these are small, hairline cracks that are of no consequence. The screed is not a structural element.


 
Polished concrete is no problem.  As for screed thickness, the thicker it is, the less reactive it is.   On my first house it was thinner than on my current one.  On my next one rolleyes: ) I'll go back to a lighter one, say 65mm.   It's easier imho to control room temps that way, given the 4-seasons-in-one-day weather we get.  All, as they say, my 0.02.


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## baldyman27 (28 Apr 2009)

galwaytt said:


> The size of the duct is immaterial - you can put it right under everything. Zero-loss pipe, and it's assoctiated duct is so stiff, and needs such a big radius to bend it, you're better off going way, way down, and coming through the floor, square.


 
I always go by what the appointed plumber wants and has agreed with the client, removes any onus of responsibility on me.





galwaytt said:


> Polished concrete is no problem. As for screed thickness, the thicker it is, the less reactive it is. On my first house it was thinner than on my current one. On my next one rolleyes: ) I'll go back to a lighter one, say 65mm. It's easier imho to control room temps that way, given the 4-seasons-in-one-day weather we get. All, as they say, my 0.02.


 
Be careful here, you could be very prone to cracking when laying under 75mm.


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## galwaytt (28 Apr 2009)

baldyman27 said:


> As well as being more expensive and totally unnecessary unless ground conditions dictate otherwise. Why would they be more accurate?


 
I don't see how you can say more expensive: they're faster to build, and labour being the cost that it is, the less time, the less expensive. No blocks, no mortar, no sand, no blocklaying labour. Poured in most housees, in half a day. Easier/faster for groundworks machinery to work on -clear the entire site, hardcore, blind, whack. No infill and infill machine/labour required, ( as there is after strip found block courses laid to backfill and whack subfloor, and no 2nd visit to pour subfloor.). Continuous radon membrane under all founds and floors, continuous, is better, and the raft is far more impervious to damp, being a contiguous 30N concrete mass. Some new constructions (e.g. Tesco in Waterford) have 300mm insulation laid under the concrete, out past the founds, to isolate the building completely from the ground.

And no, it's not unnecessary - the depths under walls is same as conventional, and the intermediate floor is no deeper, either, so there's no waste. 

A single formboard layout on the perimeter of a raft is easier and more accurate, to lay. It takes less labour. For blocklaying the walls of a house, it's less of an issue, but that's the problem with blocks - they can be stretched etc. to suit off-founds. 

MMC houses using factory components need much tighter tolerances than foundation builders are used to working to. 

[edit] within 5mm level and 5mm square on the diagonal[/edit]


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## galwaytt (28 Apr 2009)

baldyman27 said:


> I always go by what the appointed plumber wants and has agreed with the client, removes any onus of responsibility on me.


It's nothing to do with plumbing (he just wants, and needs, the tails to be where they're supposed to be), and, as in most cases, the client is reliant on the tradespeople to know, so most times the client doesn't know, either.



> Be careful here, you could be very prone to cracking when laying under 75mm.


  I hear ya, but thinner floors, smaller pipe and lower temps all need to be watched.


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## baldyman27 (28 Apr 2009)

Re: raft vs strip (sorry, don't have the patience to dissect your post!), can you explain why raft foundations are not the norm if they are so much faster, easier and cheaper? They are obviously more structurally sound which makes it even more intriguing.


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## NoIdentity (28 Apr 2009)

I had planned on strip foundations. However, I just got a call this minute from the earth mover saying that they've hit rock and will require a rock breaker.  Does this mean I will have to go with a raft foundation?


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## galwaytt (28 Apr 2009)

If I may, an example:

A strip foundation, and a raft foundation. Taken inside the last month on two sites 100m apart, in Co Galway.

Strip foundation:



Raft foundation (also note quality of ground works - grass still intact.....)





Groundworks for the strip founds started 1 month before the raft. In the length of time it took to excavate, pour strips, lay blocks in the photo, backfill & pour subfloor, the entire raft, AND HOUSE - including roof - were excavated, poured and building erected.

The raft house is currently being first-fixed services......the other house is only 4 rows of blocks high on one end.........

.....whichever way you crack a nut, if you can finish a house 3 or 4 months earlier, you'll save money.

...ok, gotta go - off to the Energy Show tomorrow to see what's what


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## galwaytt (28 Apr 2009)

baldyman27 said:


> Re: raft vs strip (sorry, don't have the patience to dissect your post!), can you explain why raft foundations are not the norm if they are so much faster, easier and cheaper? They are obviously more structurally sound which makes it even more intriguing.


 
For the same reason that the hollow concrete block is still in existence in the East........you have strip foundations. _" cos that's the way we always do them 'round here" _ 

This side of the Shannon is almost exclusively rafts, for the reasons above.




NoIdentity said:


> I had planned on strip foundations. However, I just got a call this minute from the earth mover saying that they've hit rock and will require a rock breaker. Does this mean I will have to go with a raft foundation?


 
No, not necessarily. Don't panic. Someone - or you - needs to get a look and see how much is involved. If it's a huge mass of rock, then yes a raft _may _be a better option. But for one rock, it's not a deal _breaker _(pun, sorry... )

On my own house, I had the big mass of rock thing, and the breaker was there for 4 full days...........  Nope, didn't like the bill, either...


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## baldyman27 (28 Apr 2009)

galwaytt said:


> This side of the Shannon is almost exclusively rafts, for the reasons above.


 
Nothing to do with prevailing ground conditions west of the Shannon I suppose?






galwaytt said:


> Someone - or you - needs to get a look and see how much is involved.


 
Specifically your engineer. He is ultimately responsible for the structural integrity of the house. Solid bearing will have to be found all around, even if this involves finding the rock under all areas and bringing back up to level with leanmix. Could be costly but hopefully not the case.

Galwaytt, you seem to be giving out biased and possibly self-serving advice re raft foundations and misleading advice re the presence of rock. I hope for his/her sake, that the OP isn't too impressionable.


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## wexford dude (29 Apr 2009)

galwaytt,

I am amused that you think a raft foundation is cheaper than strip foundations.It


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## wexford dude (29 Apr 2009)

galwaytt - I am amused that you think a raft foundation is cheaper than strip foundations.It may be able to compete in terms of cost if you uncover a reaonably level rock platform to build off.Surely as you discovered on your own house there was a rock breaker required for four days to create a decent platform.
 NoIdentity - in your case it may well be cheaper to do a raft if your groundworker has uncovered rock as the entire area below the house will have to cleared down to clean rock - assuming that this is not an isolated pocket of rock - further site investigation will conclude this.On a previous project - a v. large private house ,there was significant rock (granite) breaking required.There were strip foundations called up on that project, the architect thought that we could rock break to underside of hardcore and then locally rock break for the strip foundations.We were allowed to reduce the rising blockwork to 450mm (2 blocks) high thus reducing the depth of rock breaking on the high side by 225mm.We shuttered the strip foundations and then laid the rising blockwork on top.The reason that this was more cost effective as that we had 450mm of rising block on the high side and 2.475m (11 courses) on the low side - that was the profile of the rock.In fairness that was a particularly large house and the underlying rock strata at a particularly steep gradient.
On a separate standard private house the rock was shale.The strip foundations went ahead with rock breaking using a JCB required in certain areas to achieve the depth.
I would imagine in your case that the difference in rock level across your house will be alot less and I hope that you have no rock-breaking at all.

Once your groundworker has cleared off the rock under the house you will know more.You haven't mentioned if you have an engineer on board.You will need one to design the raft (if required) and to generally advise on the suitability of the rock platform.


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## wexford dude (29 Apr 2009)

galwaytt - have just looked at your photos , that's just blatant advertising.Have you no batter shots of the raft that could be blockwork for all you can see there


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## baldyman27 (29 Apr 2009)

wexford dude said:


> galwaytt,
> 
> I am amused that you think a raft foundation is cheaper than strip foundations.


 
Ah sure he has his vested interest reasons.



galwaytt said:


> ------- Declared interest: we build SIP houses on rafts all the time ----
> 
> Have a look at one of our standard details, as an example:


 
Disappointingly blatant.


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## baldyman27 (29 Apr 2009)

galwaytt said:


> Raft foundation (also note quality of ground works - *grass still intact*.....)


 
What are you trying to suggest here? That strip foundations automatically lead to more site clearance? This has nothing whatsoever to do with whether a strip or raft foundation is called up, all to do with the contractor, the site conditions, etc. Get real man and stop pushing your own agenda. You are unfairly leading people astray here.


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## kemosabe (29 Apr 2009)

Engineer & builder recommended a raft foundaton for my self-build. The reason they agreed on this was due to the changeable nature of the soil across the site. In our case the raft foundation is the better option & will reduce settlement cracks etc. Will cost approx. 1k more than strip but we believe it is money well spent in our case.


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## sydthebeat (29 Apr 2009)

kemosabe said:


> Engineer & builder recommended a raft foundaton for my self-build. The reason they agreed on this was due to the changeable nature of the soil across the site. In our case the raft foundation is the better option & will reduce settlement cracks etc. Will cost approx. 1k more than strip but we believe it is money well spent in our case.



1000 more is incredible.... you must have been getting roasted on strip foundation prices..

raft foundations increase concrete demand of about 150-200%
steel reinforcement increases on average about the same....

in my area (midlands) the difference between cost of strip founds and raft founds can be as much as 100%.... that 'may' be because they are not as popular here as they are in the west due to the wests vast underlying rock topography....

whether or not they are better is relative.... 

all foundations should be designed to suit their ground conditions... a raft in an area where strip is sufficient is a kin to breaking a nut with a hammer...


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## kemosabe (29 Apr 2009)

Im based in the midlands also, I dont work in the area so I wont attempt to contradict your figures except to say that both engineer & the builder stated that the price of raft foundations has narrowed dramatically in comparison to strip. Engineer stated that the only disadvantage to using a raft is the price, every other aspect is an advantage.
With regard to which one is better I would agree it is completely relative but I know which one I would prefer in my build & that is raft due to the soil type.


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## sydthebeat (29 Apr 2009)

interesting.... i wonder what the reason is for the narrowing of the price difference??? 
steel certainly isnt getting cheaper.... so i wonder if its the abilities of the builders which are getting better???


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## baldyman27 (29 Apr 2009)

Syd, I've found the price of steel has come down dramatically from the highs of c. E1000 not too long ago. Haven't had cause to buy cut and bent steel lately, but A393 mesh is literally half the price I paid a year ago. What it could possibly also be is the chippies labour rates for the formwork which they might price on time now rather than M2.


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## sydthebeat (29 Apr 2009)

baldyman27 said:


> Syd, I've found the price of steel has come down dramatically from the highs of c. E1000 not too long ago. Haven't had cause to buy cut and bent steel lately, but A393 mesh is literally half the price I paid a year ago. What it could possibly also be is the chippies labour rates for the formwork which they might price on time now rather than M2.



makes a lot of sense...

just adds to the realisation of how we were screwed during the 'good' times!!!


just checked and see steel hit a high around july 2008, and is now down to about 50% of that price!!!


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## baldyman27 (29 Apr 2009)

The reason steel was so high was because of China's demand. Believe it or not (I know most won't) I knew guys in 2007/2008 who *lost* money on jobs that they had priced before steel started to go crazy. These would have been jobs with a fair amount of re-inforcing and structural steel. Crazy but true.


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