Stick with rads or continue with UFH?

[sb1202]

Having doubts about UFH over rads. 

Project is an extension/annexe old stone cottage 600mm thick walls with no insulation in walls or floor, difficult to heat. Walls are in the process of being insulated. Existing rad circuit in place. 

The annexe is occasional use and my thinking was to install UFH with the Wunda retrofit system, 3 rooms, hall, & bathroom. 5 zones, with thermostats and probes. Total area 45sqm.

The existing floor is suspended chip on 50mm joists on sand & cement screed (see diagram) No insulation between joists and only 50mm space available

With the wunda retrofit, they've said just to stick the panels down over the existing chipboard and the disadvantage is that te floor height is raised by 25mm, meaning refit skirtings etc. Also, the lack of insulation beneath the chipboard has me thinking this is going to cause problems - e.g. it might need to run hotter, which is not good for an engineered wood floor and will require more to heat. 

Am I better just sticking with the existing rads and insulating the floor with 50mm pir, replacing the chipboard and installing the wood floor? Upgrading the rads. Maybe spend the money on heat recovery?

 

Any advice welcomed

[JohnMo]

Not enough insulation for UFH to be effective - stick with rads

Edited December 19 by JohnMo

[Iceverge]

Mechanical ventilation of some kind is a must. 

 

Then airtighess. 

 

Then insulation. 

 

 

Do these 3 well and heating becomes an afterthought. Keep it as simple and efficient as possible. Another vote for rads. 

 

I would avoid tiles on the floor in any case. Horrible, slippery cold things. 

[JohnMo]

27 minutes ago, sb1202 said:

Maybe spend the money on heat recovery

Only do that if you have fixed every draft and been air tested to 3 or better, otherwise that defeats most benefits.

 

If you are reasonably draft free you are better doing dMEV or MEV. Something like Greenwood CV2 or CV3 fans for dMEV and then add self modulating trickle vents. Cost pennies to run, can be bought from eBay super cheap and are just about silent - they only boost when needed and they do that automatically based on humidity. MEV same deal, but you have to run ducts to central unit.

[nod]

1 hour ago, Iceverge said:

Mechanical ventilation of some kind is a must. 

 

Then airtighess. 

 

Then insulation. 

 

 

Do these 3 well and heating. Becomes an afterthought. Keep it as simple and efficient as possible. Another vote for rads. 

 

I would avoid tiles on the floor in any case. Horrible, slippery cold things. 

Tiles are fine with UFH There’s plenty of none slip tiles Though the trend seems to be large format high gloss at the moment 

Wood is ok but extremely prone to marking and damage 

[nod]

A friend has recently used Wunda throughout there cottage Around 80 m2 Simalar scenario to you I’m not sure about the running cost 

But he’s really pleased with it 

[sb1202]

21 hours ago, Iceverge said:

I would avoid tiles on the floor in any case. Horrible, slippery cold things.

Definitely - no intention to ever use tiles. I've used foam backed LVT in a couple of areas and they are amazing. Visitors think its real tile.

[sb1202]

19 hours ago, nod said:

I’m not sure about the running cost 

But he’s really pleased with it 

That's my concern. We've got our running costs down significantly since we bought the house we're in and I'm not wanting to go back the way. 

[RHayes]

Insulate the void and then use a chipboard system like the Ambiente Jo Floor.  This is the best on build up with your system as the existing 20mm chipboard is replaced with their jo floor system which is just 22mm plus 6mm over board.  

 

Alternatively use the Ambiente AmbiDeck 20 pro.  Its 20mm insulation board so helps on floor insulation and its with 16mm pipe so ideal for heat pumps and has a very good output.  I am sure you won't be disappointed in the system and I'm very confident that it will be cheaper than a rad system.

 

On 19/12/2024 at 14:58, JohnMo said:

Not enough insulation for UFH to be effective - stick with rads

Quantity of insulation and effectiveness of UFH is not linked.  You don't have to have a certain thickness of insulation for UFH to be effective, I've got a very effective system at my house with just 50 EPS polystyrene between joists just like this and the system works beautifully.  

[JohnMo]

1 hour ago, RHayes said:

Quantity of insulation and effectiveness of UFH is not linked.  You don't have to have a certain thickness of insulation for UFH to be effective, I've got a very effective system at my house with just 50 EPS polystyrene between joists just like this and the system works beautifully.  

Shouldn't really have said effective, should have said efficient. Pump enough heat into anything it can be effective. Downwards heat loss also means more heat is always pumped into UFH than radiators - insulation depth make it cheaper than it would otherwise be to run. You can have a lower flow temperature also.

[Nickfromwales]

On 21/12/2024 at 14:23, RHayes said:

Quantity of insulation and effectiveness of UFH is not linked.  You don't have to have a certain thickness of insulation for UFH to be effective, I've got a very effective system at my house with just 50 EPS polystyrene between joists just like this and the system works beautifully.  

 

On 21/12/2024 at 15:47, JohnMo said:

Shouldn't really have said effective, should have said efficient. Pump enough heat into anything it can be effective. Downwards heat loss also means more heat is always pumped into UFH than radiators - insulation depth make it cheaper than it would otherwise be to run. You can have a lower flow temperature also.

Both are relevant points.

Effectiveness is the most relevant, as with enough downward/other losses and a max surface temp of 27°C, you can soon find yourself pumping a huge amount of energy into the subfloor vs room which means it’s fair to say that it is ineffective in the grand scheme as it’s so perverse to have chosen/be running it.

 

Efficient is where bags of insulation and airtightness makes these things perform excellently. 
 

Biggest killer will be the natural infiltration of the dwelling, as each of the above will both be useless maths if the heated air leaves via the clouds.

 

Aim to get airtight with MVHR (go with an option that has heat recovery, it’s really a no brainier if viable) and then you’ll only need a thimble of heat anyways.

 

Shift the problem instead of making the solution fit? Spend money on ‘energy saving’ not ‘energy spending’ via compensating for poor fabric performance.  

[Iceverge]

9 hours ago, Nickfromwales said:

Spend money on ‘energy saving’ not ‘energy spending’ 

 

Nice....

 

 

I'm nicking that. 

[Nickfromwales]

20 hours ago, Iceverge said:

 

Nice....

 

 

I'm nicking that. 

Merry Xmas lol. 🎅