Advise on my underfloor heating design

[Coll659]

Hello all

 

Im about to embark on a full renovation of an old house were buying and im planning to do underfloor heating throughout alongside a heat pump. since budget is very tight I will do pretty much everything by myself( im a joiner/carpenter and have some basic experince in thing like plumbing, electrics, plastering, tiling etc.). I have been researching as much as I can and think I have come up with a plan for the underfloor heating but hoping I can get some feedback/critic/advise etc. from some of you who have more experience. 

 

The house:

the house is an old house in Slovakia which has an original part constructed of thick solid block construction and a pitched roof. It then has a second half which was started as a newer extension but never finished, this is made of thick aerated block and a slab roof. Currently uninsulated but will be getting 200mm of wool exterior insulation and plaster all around as well as insulation in the ceilings. 

area: approx 120m2

 

Heat loss:

I have done my heat loss calculations as best as I can but as its an old building I have had to make some assumptions. Im also basing it on a design temperature of -10 as those temperatures are not too uncommon, certainly through the night here. I have used heat punk and calculated a heat loss of approx 5600w at -10 after I complete insulation and window changes etc. 

 

underfloor heating:

lifting the slab is not really possible and so to reduce height build up im planning 50mm of PIR board (i know more is recommended but I hope this will be sufficient, if my calculations are good then this should give me a u value of 0.23) followed by a membrane, 16mm underfloor heating pipe stapled to insulation, then a 50mm anhydrite screed. I want to run everything completely open loop.

 

So using H2x I have designed the room with the most heat loss (lounge) with 2 circuits of 150mm centres. When I reduce the flow temperature to the minimum to meet the heat demand for that room (39 flow, 34 return) I can still meet the demand of all other rooms with 200mm centres. Am I right in thinking this is the best thing to do?

 

other rooms: In the plan bellow there is no heating in the hallway, dining room and utility room but my plan is to weave the flow and returns to all the others room to fill these areas as they are only small interior areas so this will save on loops and complexity. 

 

Iv attached my plan below as well as a basic floor plan.

 

I would love to get some feedback on this from the community and appreciate any help/advise.

 

[JohnMo]

I am coming to the conclusion that you go one of two routes 

 

1. Fully insulated floor, so 150 to 200mm of PIR or equivalent.

2. Just don't bother with insulation. Clip pipes direct to slab and screed over.

 

Option 2 will only work with a ground bearing slab. Suspended floor will be a money pit.

 

So option 2, you engage the soil below the house to buffer heat. You run WC mode 24/7 with no zones. The heat stored in the ground should help get through the cold snaps.

 

With the above in mind, you need to run the lowest flow temp you can, so close spacing will be better than wide spacing. Use 16mm pert-al-pert pipe, suitable manifold and no pump or mixer and no buffer or volumiser.

 

First sensible person seen, so far with a plan

44 minutes ago, Coll659 said:

hallway, dining room and utility room but my plan is to weave the flow and returns to all the others room to fill these areas

 

[JohnMo]

48 minutes ago, Coll659 said:

can still meet the demand of all other rooms with 200mm centres. Am I right in thinking this is the best thing to do?

Yes, will make balancing way easier.

[Coll659]

Thanks for the reply John I appreciate it. 

 

I had thought about your idea of the no insulation route and have seen a little talk of this approach on this forum but wasn't sure about it. The slab as far as I can tell is pretty deep, especially since it's built in sloping ground. I would say at least a meter.  would a temperature of 39c be ok for a constant heating mode? And would I be right that once I hear the slab (which could take some time at the beginning of winter) then running costs would be similar as long as I keep it running? 

 

Thanks again

 

Colin

[Nickfromwales]

Agree that the 50mm of insulation would just be wasted head height and cost as it would add much value for performance numbers. At that thickness the heat will only penetrate downwards so far and then the whole thing becomes the heated emitter. 
 

One of those instances where “it is what it is”. 

 

With a heat pump and a decent chuck of slab you’ll get where you get to and just accept the losses, and then you can have less screed on top too as you’ll just want to cover the 16mm pipes by 15-20mm for a level floor to be applied.

 

Definitely won’t be something to ‘turn off’ though, as you’re looking at days to get this up to a temp where it’s useful as space heating I expect.

[nod]

Warmup will do you a full heating design Free of charge 

[JohnMo]

1 hour ago, nod said:

Warmup will do you a full heating design Free of charge 

But his design is already way better than a cut and paste job he would get from them. So why would you bother?

[nod]

5 minutes ago, JohnMo said:

But his design is already way better than a cut and paste job he would get from them. So why would you bother?

Because At the very least 

It would confirm that 

[Coll659]

2 hours ago, Nickfromwales said:

Agree that the 50mm of insulation would just be wasted head height and cost as it would add much value for performance numbers. At that thickness the heat will only penetrate downwards so far and then the whole thing becomes the heated emitter. 
 

One of those instances where “it is what it is”. 

 

With a heat pump and a decent chuck of slab you’ll get where you get to and just accept the losses, and then you can have less screed on top too as you’ll just want to cover the 16mm pipes by 15-20mm for a level floor to be applied.

 

Definitely won’t be something to ‘turn off’ though, as you’re looking at days to get this up to a temp where it’s useful as space heating I expect.

Thanks very much for the advice, so another vote for no insulation, I'll definitely need to consider this approach. 

[Coll659]

2 hours ago, nod said:

Warmup will do you a full heating design Free of charge 

Thanks I'll take a look at them. 

[Nickfromwales]

1 hour ago, Coll659 said:

Thanks I'll take a look at them. 

They’ll tell you to F O in the 1st 5 seconds when you tell them what your setup needs to deal with.

[Mr Punter]

Could you fit any external perimeter insulation?  It would involve excavating a trench around the house and filling with EPS insulation. It could marry up with your proposed 200mm EWI.

[Coll659]

28 minutes ago, Mr Punter said:

Could you fit any external perimeter insulation?  It would involve excavating a trench around the house and filling with EPS insulation. It could marry up with your proposed 200mm EWI.

Yeah for sure I could do that. I have just been looking again at the house with this in mind and took done photos. Hopefully it's clear in photos but from what I can tell the older part has approx 1m above ground (to nothing at the back of the house) of stone foundation then a 100mm slab followed by the dpc and walls. 

 

The newer part is also about a meter of concrete slab (to nothing at back again) exposed above ground followed by dpc and walls. 

 

So if I insulate these well (and dig down at the back to insulate below ground as you suggest) do you think it's feasible to do this one without huge running costs? 

 

 

[Coll659]

And the newer part: 

[Nickfromwales]

1 hour ago, Coll659 said:

do you think it's feasible to do this one without huge running costs? 

Insulate, insulate, insulate.

 

Airtightness (killing off excess cold air infiltration) will trump 1000mm of insulation so we need to be practical when giving advice.

 

Ultimately you should be putting 50mm of insulation (IWI) to the walls & floors and putting carpet down, and fitting radiators, if you want a comfortable home with reduced running costs. 

[Coll659]

Thanks.

 

I really want to avoid the radiators unless absolutely necessary. running costs is important and I want to make it as good as I can while im renovating just now but its not the only factor anf given our budget and age of the house I can accept some higher running costs, as long as its not going to be super high.  I will be putting at least 200mm exterior insulation around foundations as well as exterior walls anyway so hopefully this will be sufficient. 

 

I will need to do more research on getting good airtightness, I am replacing all doors and windows with triple glazing and will make sure they are sealed. I will also be plastering inside as well as the exterior below and above insulation. then need to figure out how to block up any holes. 

[Nickfromwales]

35 minutes ago, Coll659 said:

Thanks.

 

I really want to avoid the radiators unless absolutely necessary. running costs is important and I want to make it as good as I can while im renovating just now but its not the only factor anf given our budget and age of the house I can accept some higher running costs, as long as its not going to be super high.  I will be putting at least 200mm exterior insulation around foundations as well as exterior walls anyway so hopefully this will be sufficient. 

 

I will need to do more research on getting good airtightness, I am replacing all doors and windows with triple glazing and will make sure they are sealed. I will also be plastering inside as well as the exterior below and above insulation. then need to figure out how to block up any holes. 

That’s all good, but remember that you’ll need to install MVHR if you want to seal the place up well eg no trickle vents on windows or mechanical extractor fans for kitchen and bathrooms etc.

[Coll659]

12 minutes ago, Nickfromwales said:

That’s all good, but remember that you’ll need to install MVHR if you want to seal the place up well eg no trickle vents on windows or mechanical extractor fans for kitchen and bathrooms etc.

 Thanks. yeah I'm looking into this just now and my options

[JohnMo]

49 minutes ago, Coll659 said:

really want to avoid the radiators unless absolutely necessary. running costs is important

For me, where you are located with cold winter and assume pretty hot summers - I would look at fan coils and not at UFH 

 

Add 50mm of floor insulation to take away the cold feeling of the floor.

 

Set heat pump to 35 degs in winter and about 14 in summer.  Or 6 with condensation drainage under fan coil.

[Coll659]

2 minutes ago, JohnMo said:

For me, where you are located with cold winter and assume pretty hot summers - I would look at fan coils and not at UFH 

 

Add 50mm of floor insulation to take away the cold feeling of the floor.

 

Set heat pump to 35 degs in winter and about 14 in summer.  Or 6 with condensation drainage under fan coil.

 

hmm I had thought about it due to the air conditioning effect in summer (which does get extremely hot).

Will need to look into costs and efficiency of these as i dont really know anything about them but will definitely do some research. thanks for the advice

 

[JohnMo]

eBay has some bargains for fan coils.

 

Our summer house has one, switched cooling yesterday and running at no lower than 13.5 degs flow temperature the summer house was 8 degs cooler at 5pm the previous day and when solar gain finished dropped to 21 very quickly.

 

You can use UFH for cooling, but not as effective.

[Coll659]

Thanks for all the advice so far, it's been really helpful. 

 

Whist I tried to sell the merits of fan coils to my wife we are still pretty committed to underfloor heating.

 

After going over all floor and ceiling levels again yesterday I figured I could manage 100mm of insulation throughout all of the older part of the house and half of the newer part (maybe even 200mm in bathroom) leaving me only two rooms (living and bedroom making up approx 28m2 together) where I can only manage 50mm insulation. Would it make sense to do this and maybe do 100mm centres in the rooms with 50mm insulation and 150mm everywhere else.

Coupling the slab does seem like a good option as well but thinking with 100mm of insulation through 80% of the house this might be a more economical option. 

Edited May 2 by Nickfromwales

[Nickfromwales]

2 hours ago, Coll659 said:

Thanks for all the advice so far, it's been really helpful. 

 

Whist I tried to sell the merits of fan coils to my wife we are still pretty committed to underfloor heating.

 

After going over all floor and ceiling levels again yesterday I figured I could manage 100mm of insulation throughout all of the older part of the house and half of the newer part (maybe even 200mm in bathroom) leaving me only two rooms (living and bedroom making up approx 28m2 together) where I can only manage 50mm insulation. Would it make sense to do this and maybe do 100mm centres in the rooms with 50mm insulation and 150mm everywhere else.

Coupling the slab does seem like a good option as well but thinking with 100mm of insulation through 80% of the house this might be a more economical option. 

100mm in general will be much better, 200mm is passive levels, and for the areas with 50mm I guess just suck it up.

 

Yes to the 100mm centres for the 50mm insulated areas, 150mm everywhere else may make it tricky to balance without zoning and putting stats per room / space. Consider running some numbers for going 200mm in the areas with 100 and 200(?)mm of insulation so you don’t get overshoot in those areas for the same flow temp. 

[Coll659]

Thanks very much for the help. I'll run some more numbers and scenarios using heatpunk and h2x to figure out the best spacing as you suggest