Underfloor Heating - the biggest con ever

spud

Our very well insulated house was built 10 years ago with wet UFH downstairs and rads upstairs. It works brilliantly for us allowing zoned room heating downstairs. Yes, you need to use it differently than rads but you soon get used to the change and contributes to a very low gas usage of 6000kw or so per year in a large 5 bed house. So it isn’t a con but would agree retrofitting into non well insulated houses would not work anywhere near as well.  

Chickereeeee

I don't really know why UFH is called 'radiant' anyway, as most heat dleivery would be via conduction or convection. 

ComicGeek

Chickereeeee said:

I don't really know why UFH is called 'radiant' anyway, as most heat dleivery would be via conduction or convection. 

UFH is typically 60% radiant, 40% convective - however the heat has to be delivered to the surface of the floor via conduction before being delivered as radiant and convective heat.

Radiators are typically 70% convective and 30% radiant. 

mcplumb

Retro fit UFH, I probably wouldn't bother with. In a new build with MVHR I can't think of a better solution (other than if the customer tiles the whole ground floor - flow temps are so low you need a cold day/increased flow temp to take that edge off). From experience customers love UFH because they have warm floors, in an energy efficient house those floors will barely get warm - to get a warm floor you need to open a window and reduce air temp

daveyjp

My parents have had it in their bungalow since a full refurb about 10 years ago.  Its a 5 stat system.  Lounge, two bedrooms, kitchen and bathroom.

Works from a standard combi, every room individually controlled (lounge at 20, elsewhere at 18) and because the solid floor and screed is a heat sink it is very efficient once warmed through, which begins in late Autumn when they set the heating water temp to 45 degrees.  Previously the property had a suspended timber floor throughout with no insulation.

I've been there in mid winter and they have had lounge windows open to cool the lounge down, even though the heating isn't operating.

grumbler

daveyjp said:

... it is very efficient once warmed through, which begins in late Autumn when they set the heating water temp to 45 degrees. 

I've been there in mid winter and they have had lounge windows open to cool the lounge down, even though the heating isn't operating.

This means exactly the opposite - it is very inefficient. They spent a lot of energy on heating tons of screed, then have to open windows to cool the screed instead on simply switching off the radiators should they had them.

Rosa_Damascena

I have yet to feel the sustained benefits of UFH, and am unlikely to given the cost of fuel now.

I will be heating myself rather than the space around me.

Chickereeeee

ComicGeek said:

Chickereeeee said:

I don't really know why UFH is called 'radiant' anyway, as most heat dleivery would be via conduction or convection. 

UFH is typically 60% radiant, 40% convective - however the heat has to be delivered to the surface of the floor via conduction before being delivered as radiant and convective heat.

Radiators are typically 70% convective and 30% radiant. 

I still doubt that. With no evidence whatsoever, I would have though that heating the air local to the floor would account for most of the heating effect. 

grumbler

Chickereeeee said:

ComicGeek said:

Chickereeeee said:

I don't really know why UFH is called 'radiant' anyway, as most heat dleivery would be via conduction or convection. 

UFH is typically 60% radiant, 40% convective - however the heat has to be delivered to the surface of the floor via conduction before being delivered as radiant and convective heat.

Radiators are typically 70% convective and 30% radiant. 

I still doubt that. With no evidence whatsoever, I would have though that heating the air local to the floor would account for most of the heating effect. 

Why? Any hot object both radiates the heat and heats the surrounding air. The former depends a on the colour - dark surfaces radiate more, so 40/70 are, of course not the exact figures. Neither are 70/30 - this depends a lot on the design. Radiators with hidden heat exchanges radiate very little.

A hot  flat radiator without any extra heat exchanger radiates the same power as the same area of hot floor with the same temperature and colour.  Heating by convection can differ as it depends on the air flow and thus on the orientation of the hot surface. Vertical surface is more efficient for convection.

ComicGeek

Chickereeeee said:

ComicGeek said:

Chickereeeee said:

I don't really know why UFH is called 'radiant' anyway, as most heat dleivery would be via conduction or convection. 

UFH is typically 60% radiant, 40% convective - however the heat has to be delivered to the surface of the floor via conduction before being delivered as radiant and convective heat.

Radiators are typically 70% convective and 30% radiant. 

I still doubt that. With no evidence whatsoever, I would have though that heating the air local to the floor would account for most of the heating effect. 

Fortunately science isn't based on random thoughts, so thermodynamics still functions as the universe intended despite some people not believing it. 

The temp of the UFH floor surface is relatively low, normally 26-27 degrees, so the convective effect is limited by the amount of heat that the air can pick up to generate convective currents. Compare that to a radiator which might be 70 degrees. That's the difference. Also the fact that the parts of the room furthest from the radiator will be much colder, and that drives the convective currents, and particularly if the radiator is under a cold window. 

Then think about the physical area of the heated floor compared against the front face of the radiator that you would see - even though the floor is not as hot, the radiant effect is provided by the sheer size of the floor.