Which Heating System???

[NoIdentity]

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??

 

[galwaytt]

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) ?

 

[NoIdentity]

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).

 

[NoIdentity]

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

 

[baldyman27]

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.

 

[wexford dude]

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.

 

[NoIdentity]

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

 

[NoIdentity]

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.

 

[baldyman27]

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.

 

[baldyman27]

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.

 

[NoIdentity]

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?

 

[baldyman27]

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.

 

[galwaytt]

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.

- 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.

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:

 

[baldyman27]

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?

 

[galwaytt]

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.

 

[baldyman27]

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.

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.

 

[galwaytt]

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]

 

[galwaytt]

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.

 

[baldyman27]

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.

 

[NoIdentity]

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?