Probe - air or in floor?

[curlewhouse]

Fitting a Wunda system and whilst downstairs is a 100mm thick screed, and air temp thermostats in each room, the upstairs bathroom is to be fitted out with those EPS foil faced panels. The supplied probe can be mounted in its own little box to measure air temperature, or in the floor itself.   I wondered what peoples views were on the best option? It occurs to me that it is the air temperature after all which matters the most, and as they show the probe has to be let into the EPS then I'm not sure how good a reflection the heat there will be in relation to the air temperature.  There will be ceramic tiles on top. Its available as a probe so you can use it safely in a wet room . 

Any thoughts to preference? 

In this plan position B wall mounted would get the wet room (no door)/shower area temp ,  position A would again wall mounted and I think give the whole room more accurately and position C is where Wunda suggest the probe goes if I fit it underfloor. 

 

Edited February 26, 2018 by curlewhouse

[le-cerveau]

Jeremy's experience in slab control shows that air temperature is just as effective and less complicated, as you say it is the temperature you are after.  The only reason I can see for putting it in the slab is as a limit probe, if you can run the floor that hot!

 

Personally 'A' gives you the most balanced result.

[SteamyTea]

I think that a bathroom is probably a special case.

There is high humidity to deal with as well as a greater temperature swing over short periods of time.

Then you have greater air changes an hour.

Then you are not using the room for several hours at all.

 

So I suspect that monitoring the air is more important than the slab temperature.

 

Normally you want to balance the energy input with the energy output, this is not really possible with a bathroom.

[jayroc2k]

Based on my experience? Definitely in the floor for bathrooms as you want to be able to “force” the heating on to warm the tiles regardless of the actual temp in the space. I am having to set mine at almost 25deg just to get the floors to warm up. 

[SteamyTea]

1 minute ago, jayroc2k said:

Based on my experience? Definitely in the floor for bathrooms as you want to be able to “force” the heating on to warm the tiles regardless of the actual temp in the space.

I am still pondering this.

If you don't mind the bathroom always hotter than the optimum for comfort and drying out, then yes, stick it in (or close to) the slab/floor/tiles/whatever and just set it to a high temperature.

To a certain extent the extractor fan, with or without MVHR, will draw in cooler air.  If this is not optimum, but it more likely to be too hot than cold, then probably not a problem, though not the most energy efficient method.

The most energy efficient is to control the air temperature and that involves balancing the thermal inertia of the floor with the total mass of air that need heating, and the temperature of that air.  Only local history will tell you the optimum setting to get that right.