Could underfloor heating be more trouble than its worth?

[Spoilt Victorian Child]

I've been looking at underfloor heating, specifically this 'overfloor' type, which actually fits over the top of existing floors, so no need to take floorboards up:
http://www.easyfitfloorheating.co.uk/easyfit-floor-heating/

The company claims less than 10% of the system's heat output is lost downwards into the existing floor, but that still means the air beneath the suspended part of my kitchen floor is going to get heated.

The thing I'm wondering is if the warmer air that's created under the floor would likely affect the venting to the sub-floor in adjacent rooms. Ie, would it push or trap the colder air in some way that may cause damp problems later on?

Here's a rough plan of the downstairs:

The green arrows indicate airbricks, 3 at the front and 3 at the back.
The grey fill is a concrete floor, all the rest is suspended floor.
The red snake is the proposed underfloor heating, which may affect the integrity of two of the rear vents?

Any thoughts? I may be making a mountain out of a molehill here, but I'd like to be sure before committing time and money to it!

 

[Zebra]

My own opinion, not that I know that much about sub-floor ventilation, is that the specific concern you raise is not significant. The usual issue with warming ventilated cold spaces is not to do with the temperature per se, but that warm air escapes from within the house, containing moisture which then condenses on a cold surface. You will not be bringing warm air from inside the house to underneath the floor. The temperature under the floor would fluctuate in any case, according to the seasons, so I can't see a problem with that.
Whether this particular flooring is a good idea for other reasons though, I really couldn't say. I've not heard of these panels. I'd imagine that without a great deal of insulation under them, you will be losing heat to under the floor. I would be wanting to know more about their genuine efficiency, from people who've used them before, not just the statistics stated by the manufacturer.

 

[Penners]

The thing I'm wondering is if the warmer air that's created under the floor would likely affect the venting to the sub-floor in adjacent rooms. Ie, would it push or trap the colder air in some way that may cause damp problems later on?

While I claim no specialist knowledge, I find it difficult to imagine that this would be the case. When two bodies of air at different temperatures come together in an area where ventilation causes air movement, I suspect that the tendency is for them to mix and roughly average out the temperature.

I think my concern about this plan would be the amount of heat that you will lose downwards into the concrete and the sub-floor void. Why don't you contact the suppliers, give them the details of your floor/sub-floor structure and ask them to give you an estimate of the proportion of the heat that will be thus lost? If they won't do this, then you may have cause for concern.

 

[Spoilt Victorian Child]

Why don't you contact the suppliers, give them the details of your floor/sub-floor structure and ask them to give you an estimate of the proportion of the heat that will be thus lost? If they won't do this, then you may have cause for concern.

I did do this, that's where I got the 'less than 10% lost' figure from. I too am slightly sceptical, but all the online reviews I can find for this product via Google are favourable. I explained that one half of the floor is concrete and the other suspended, as I wondered if I'd be able to feel the difference, but they claimed I shouldn't.

Guess I need to find all this in writing.