Adding underfloor heating to concrete floor
Discussion
hairyben said:
You fail to understand the information in your link, which clearly states 15% through the floor is for an average house. The average house has gas central heating and convector radiators. Hope this helps you in designing your systems.
Radiant underfloor heating will have completely different heat loss characteristics to the average house due to the floor itself being the radiator. Heat will be conducted away, not gently radiated as per average house. If you don't insulate between an element and a concrete slab, apart from crippling heat conduction losses you'll be looking at several hours for warm-up. I've installed elements or supplies for such in this way as the client/clients builder was to arrogant to take advice and I believe all such systems aren't in use due to the fact you pretty much need to run them 24/7 for them to be warm when you need them.
The only exception will be if the area is a fairly recent build as insulation in incorporated within the floor (if it's done to regs).
Sorry Ben, pleased you looked at the link but I think you have misunderstood as well - lets agree to differ eh - I have had this debate for years and dont agree. The industry has been struggling with retrofitting insulation to floors for years - ever heard of a grant for insulating a floor - No? http://www.hastingstrust.com/pdfs%20for%20download...Radiant underfloor heating will have completely different heat loss characteristics to the average house due to the floor itself being the radiator. Heat will be conducted away, not gently radiated as per average house. If you don't insulate between an element and a concrete slab, apart from crippling heat conduction losses you'll be looking at several hours for warm-up. I've installed elements or supplies for such in this way as the client/clients builder was to arrogant to take advice and I believe all such systems aren't in use due to the fact you pretty much need to run them 24/7 for them to be warm when you need them.
The only exception will be if the area is a fairly recent build as insulation in incorporated within the floor (if it's done to regs).
Firstly I have yet see any UFH system radiate heat. Heat produced is conducted (minimal) convected (mostly).
Secondly Heat loss is defined by the laws of physics a function of area, thermal resistance and temperature differential - not how well or what system is used to heat a space. Insulating a floor will increase its U value (true) and reduce heat loss (true) but percentage benefit is much smaller than for insulation added to walls, roofs, doors, windows as the temperature differential is smaller by a magnitude of at least x10 but realistically in the UK more like x15. Simple laws of physics (Q = U A(Tout-Tin)). By adding insulation you will reduce the heat loss typically by arround 0.5% to 0.25% on the floor so retrofit payback is around 30-40years.
To the OP I stand by my comments and experience in my 130 year old house - insulating floors is great if you are chopping up the floor anyway - if not then lay electric mat on top and overtile. It works!
psychoR1 said:
Sorry Ben, pleased you looked at the link but I think you have misunderstood as well - lets agree to differ eh - I have had this debate for years and dont agree. The industry has been struggling with retrofitting insulation to floors for years - ever heard of a grant for insulating a floor - No? http://www.hastingstrust.com/pdfs%20for%20download...
Firstly I have yet see any UFH system radiate heat. Heat produced is conducted (minimal) convected (mostly).
Secondly Heat loss is defined by the laws of physics a function of area, thermal resistance and temperature differential - not how well or what system is used to heat a space. Insulating a floor will increase its U value (true) and reduce heat loss (true) but percentage benefit is much smaller than for insulation added to walls, roofs, doors, windows as the temperature differential is smaller by a magnitude of at least x10 but realistically in the UK more like x15. Simple laws of physics (Q = U A(Tout-Tin)). By adding insulation you will reduce the heat loss typically by arround 0.5% to 0.25% on the floor so retrofit payback is around 30-40years.
To the OP I stand by my comments and experience in my 130 year old house - insulating floors is great if you are chopping up the floor anyway - if not then lay electric mat on top and overtile. It works!
Insulating the floor is not about insulating the room though, so a rooms heat loss calcs are irrelevant. It's about stopping the heat being wasted at source via thermal conduction. Firstly I have yet see any UFH system radiate heat. Heat produced is conducted (minimal) convected (mostly).
Secondly Heat loss is defined by the laws of physics a function of area, thermal resistance and temperature differential - not how well or what system is used to heat a space. Insulating a floor will increase its U value (true) and reduce heat loss (true) but percentage benefit is much smaller than for insulation added to walls, roofs, doors, windows as the temperature differential is smaller by a magnitude of at least x10 but realistically in the UK more like x15. Simple laws of physics (Q = U A(Tout-Tin)). By adding insulation you will reduce the heat loss typically by arround 0.5% to 0.25% on the floor so retrofit payback is around 30-40years.
To the OP I stand by my comments and experience in my 130 year old house - insulating floors is great if you are chopping up the floor anyway - if not then lay electric mat on top and overtile. It works!
For example you don't put foil behind radiators to increase a rooms U-value, as 1 meter of foil would make little difference if you have 20 meters of exterior wall. You put it there to reflect the heat being radiated back into the room.
Ben - as I said lets agree to differ - There is a negligible radiant heat from a convective UFH system.
I think you are trying to say that the insulation actually isolates the downward coductive element which true it does but only partially because it still conducts to a reduced level. The reallity is that the UFH system actually heats the floor anyway and uses that to convect into the room.
I maintain that you dont need the insulation - it really isnt neccessary and doesnt add much to performance.
If you size the system based on your losses it works without.
I think you are trying to say that the insulation actually isolates the downward coductive element which true it does but only partially because it still conducts to a reduced level. The reallity is that the UFH system actually heats the floor anyway and uses that to convect into the room.
I maintain that you dont need the insulation - it really isnt neccessary and doesnt add much to performance.
If you size the system based on your losses it works without.
psychoR1 said:
Ben - as I said lets agree to differ - There is a negligible radiant heat from a convective UFH system.
I think you are trying to say that the insulation actually isolates the downward coductive element which true it does but only partially because it still conducts to a reduced level. The reallity is that the UFH system actually heats the floor anyway and uses that to convect into the room.
I maintain that you dont need the insulation - it really isnt neccessary and doesnt add much to performance.
If you size the system based on your losses it works without.
I'm happy to agree to differ on topics such as whether the spice girls are better than the pet shop boys, or what whether curry is better than pizza, because they're both subjective. What we're argueing about is a scientific fact. Although I'm not going to make it one of those long stupidly drawn out forum bickerfests that ends up in the nth degree of pointlessness, but I want to understand and I'm happy to be proven wrong too, if it means I've learnt something.I think you are trying to say that the insulation actually isolates the downward coductive element which true it does but only partially because it still conducts to a reduced level. The reallity is that the UFH system actually heats the floor anyway and uses that to convect into the room.
I maintain that you dont need the insulation - it really isnt neccessary and doesnt add much to performance.
If you size the system based on your losses it works without.
So lets do a high school experiment, we put identical two cups of tea at 100c on a stone slab in a room at 20c. One has a cork coaster beneath it, one doesn't. This mirrors our UFH debate in that they're both emmitting heat to the surrounding area but one is protected from downward losses. You're saying both cups will cool down at exactly the same rate, no?
Ben - the points I have made all relate to my opinion of how effective the insulation is in reducing heat loss through the floor. I have said insulation makes minimal difference to the U value and supported my comment by referencing a report that highlights this and goes on to reference payback periods for floor insulation.
I think my comments are clear and for the OP to add to his deliberations and look at the links.
I am happy though to see the results of your scientific experiment and will be impressed if you can tell me what the difference in rate of heat loss will be from the base of the coffee cup with and without cork and what that means in the real world?
By the way in my years of designing and specifying HVAC systems I have never called for floor insulation beyond bldg regs, foil behind rads or cork under my coffee in site meetings!
I also think you could make a decent spice if you mixed and matched the best features from each.
I think my comments are clear and for the OP to add to his deliberations and look at the links.
I am happy though to see the results of your scientific experiment and will be impressed if you can tell me what the difference in rate of heat loss will be from the base of the coffee cup with and without cork and what that means in the real world?
By the way in my years of designing and specifying HVAC systems I have never called for floor insulation beyond bldg regs, foil behind rads or cork under my coffee in site meetings!
I also think you could make a decent spice if you mixed and matched the best features from each.
You still referring to generalised heat loss, not the heat the that will be conducted away from a heated floor. Do you really not understand the difference?
Heat loss will be greatest where it's hottest, ie where the heat is generated. If you thermal image a house with a working fireplace there'll be a huge hotspot on the outside wall where the fireplace backs onto. Your generalised heat loss calcs are irrelevant to this. If you can't understand that, you're the perfect example of the man-in-charge who can quote all the regs and equations and theory but has no working knowledge of how any of it relates to the building itself.
In the "real world" it's a simplified experiment to show whether heat loss will occur through the base, are you saying you don't understand the parallels with a thermally heated floor with/without insulation underneath?
Heat loss will be greatest where it's hottest, ie where the heat is generated. If you thermal image a house with a working fireplace there'll be a huge hotspot on the outside wall where the fireplace backs onto. Your generalised heat loss calcs are irrelevant to this. If you can't understand that, you're the perfect example of the man-in-charge who can quote all the regs and equations and theory but has no working knowledge of how any of it relates to the building itself.
psychoR1 said:
and will be impressed if you can tell me what the difference in rate of heat loss will be from the base of the coffee cup with and without cork and what that means in the real world?
I said nothing about "establishing the rate of heat loss" through the base, only that it's significant, which is the point we disagree on.In the "real world" it's a simplified experiment to show whether heat loss will occur through the base, are you saying you don't understand the parallels with a thermally heated floor with/without insulation underneath?
hairyben said:
So lets do a high school experiment, we put identical two cups of tea at 100c on a stone slab in a room at 20c. One has a cork coaster beneath it, one doesn't. This mirrors our UFH debate in that they're both emmitting heat to the surrounding area but one is protected from downward losses. You're saying both cups will cool down at exactly the same rate, no?
Which one increases the heat of the room and for how long would be my question.I fitted electric underfloor heating in our bathroom early this year.
100mm celotex in between joists, 2 layers of 12.5mm ply laid at 90 degrees to each other, with the heating on top. Tiled with 12mm travertine using flexible Ardex adhesive and grout.
It works beautifully, about 30-40 minute warm up time and the thermostat is great.
It's the only heating we have to pay for in our whole house so I'm slightly naive about the running costs but I don't think it's too bad, really. I will be able to tell you accurately after the winter!
I used: http://www.heatmat.co.uk/ and fitted it myself. Got my electrician friend to wire it up.
Just constantly checked with a multi-meter during fitting and tiling!
100mm celotex in between joists, 2 layers of 12.5mm ply laid at 90 degrees to each other, with the heating on top. Tiled with 12mm travertine using flexible Ardex adhesive and grout.
It works beautifully, about 30-40 minute warm up time and the thermostat is great.
It's the only heating we have to pay for in our whole house so I'm slightly naive about the running costs but I don't think it's too bad, really. I will be able to tell you accurately after the winter!
I used: http://www.heatmat.co.uk/ and fitted it myself. Got my electrician friend to wire it up.
Just constantly checked with a multi-meter during fitting and tiling!
Sorry Ben you've got it wrong - heat loss is greatest where the temperature difference is greatest and that is when insulation works. So the lower the temperature difference the lower the loss and the less need for insulation.
Note I haven't insulted you yet or thrown any speculation about your competence - I' m out - hope the OP looks at the info and makes his own mind up 😉
Have fun with your experiments and answer the question in the thread above about how much heat from your experimental coffee is lost through the floor pls?
Note I haven't insulted you yet or thrown any speculation about your competence - I' m out - hope the OP looks at the info and makes his own mind up 😉
Have fun with your experiments and answer the question in the thread above about how much heat from your experimental coffee is lost through the floor pls?
Well, the B&Q designer decided a good place for ours was placed in a 100mm gap between a kitchen unit and an end wall 
No room otherwise (more or less a galley shape). I will ask around about the polypipe, seems a good option. The room could stand being lifted very slightly.
The kitchen already contains the gas boiler, so it is warmed slightly by it.
I am a bit confused by the stuff in this thread about concrete etc. The UFH (polypipe wet or electric) sits on top of the concrete slab and with tiles on top of it.
So half the UFH is heating the top of the concrete floor presumably wastefully (but it will still retain/radiate a bit of heat) and the other half is heating the tiled floor to slightly better effect ?
I never quite paid attention during radiation/convection/conduction lessons, so laymans terms please
No room otherwise (more or less a galley shape). I will ask around about the polypipe, seems a good option. The room could stand being lifted very slightly.
The kitchen already contains the gas boiler, so it is warmed slightly by it.
I am a bit confused by the stuff in this thread about concrete etc. The UFH (polypipe wet or electric) sits on top of the concrete slab and with tiles on top of it.
So half the UFH is heating the top of the concrete floor presumably wastefully (but it will still retain/radiate a bit of heat) and the other half is heating the tiled floor to slightly better effect ?
I never quite paid attention during radiation/convection/conduction lessons, so laymans terms please
psychoR1 said:
Sorry Ben you've got it wrong - heat loss is greatest where the temperature difference is greatest and that is when insulation works
Which would be the floor, right?psychoR1 said:
Note I haven't insulted you yet or thrown any speculation about your competence ?
the snide remarks about coffee cups were what then?Anyway, I've asked you repeatedly to no avail so it's reasonable to presume you simply don't/can't grasp the difference between room heat loss calcs and insulating the element itself and I can't explain it any clearer than I've tried, so I'm out. I too hope the OP does his research.
Underfloor heating is what I do - as it suits NZ conditions when using a heat pump (by far the lowest cost method here).
Downward heat losses in an uninsulated floor slab can't really occur - unless you have a river running under the house.
Certainly a lot of heat will be conducted downwards if there is no insulation - but it doesn't disappear - eventually it will come back out again. The result is that without insulation reaction times will be a lot longer - and some installs will cost more to run as effectively the floor can end up being heated when not required.
Bear in mind wet underfloor must NOT have water over 45c - and most radiator systems require say 60c water - just a small complication to take into account.
Given the choice underfloor is always the way to go for heating, by comparison radiators or hot air systems are way behind for comfort levels. It's all about the radiant effect........
Hands up how many drivers have the face vents in a car blasting out hot air in winter with the feet ones turned off - and how many have cold air blasting on their feet in summer? So why heat a house this way?
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