gc100 Posted November 21, 2022 Share Posted November 21, 2022 Any recommendations? I have Heatmiser controls in each room and they are saying 22 degrees however the MVHR is saying the exhaust air is 19 and it feels a bit on the cooler side. I have no faith in these heatmiser giving an accurate temp reading. I've had a look on amazon, but its all Chinese stuff and I have no faith it will be accurate either. Any suggestions? If I search calibrated thermometers, most seem to have probes and start at £50 upwards which is a but much for what Im after! Thanks! Link to comment Share on other sites More sharing options...
PeterW Posted November 21, 2022 Share Posted November 21, 2022 Which Heatmiser ..?? Some use 230v and can create a lot of localised heat in the stat which affects the readings. MVHR won’t be accurate either as it will be measuring flowing air not static plus they will probably just have a cheap ish bulb thermistor in them. Link to comment Share on other sites More sharing options...
gc100 Posted November 21, 2022 Author Share Posted November 21, 2022 1 hour ago, PeterW said: Which Heatmiser ..?? Some use 230v and can create a lot of localised heat in the stat which affects the readings. MVHR won’t be accurate either as it will be measuring flowing air not static plus they will probably just have a cheap ish bulb thermistor in them. This one https://www.theunderfloorheatingstore.com/heatmiser-slimline I'm sure its no where near accurate Link to comment Share on other sites More sharing options...
PeterW Posted November 21, 2022 Share Posted November 21, 2022 Yeh there is an issue with those that there is a transformer in the back and no way for heat to dissipate .. Think someone did some sort of hack to cut fins in the top and bottom edge once ..? Link to comment Share on other sites More sharing options...
Radian Posted November 21, 2022 Share Posted November 21, 2022 6 minutes ago, PeterW said: Yeh there is an issue with those that there is a transformer in the back and no way for heat to dissipate .. Brilliant. My last commercially produced device like this was battery operated. No chance of that self-heating. Link to comment Share on other sites More sharing options...
SteamyTea Posted November 21, 2022 Share Posted November 21, 2022 Why not something like this https://www.ebay.co.uk/itm/113641431380 Link to comment Share on other sites More sharing options...
gc100 Posted November 21, 2022 Author Share Posted November 21, 2022 3 minutes ago, SteamyTea said: Why not something like this https://www.ebay.co.uk/itm/113641431380 Lots of those on amazon. I just presume given the price they are not going to be very accurate (or a least within 1 degree) Link to comment Share on other sites More sharing options...
gc100 Posted November 21, 2022 Author Share Posted November 21, 2022 49 minutes ago, PeterW said: Yeh there is an issue with those that there is a transformer in the back and no way for heat to dissipate .. Think someone did some sort of hack to cut fins in the top and bottom edge once ..? Yes I remember that. I really cannot be bothered to go around the house and do that to all of them. I'd just like to know what they are over/under reading by. Link to comment Share on other sites More sharing options...
Alan Ambrose Posted November 21, 2022 Share Posted November 21, 2022 Hi, Reasonably accurate thermometers are not inexpensive. I bought a second hand Tek DTM900 for not much years ago and it is quite useful. I've used it to set the temperature adjustment on about a dozen Heatmiser stats. The deal is that simple temperature sensors (thermistors etc) are cheap but only accurate to say +-2 degrees C. Thermocouples are better but they generally read with respect to room temperature and so they need 'cold junction compensation' and it's pricey to do that well. RTDs (e.g. PT100) are much better and simpler and the sensor itself is £10-100. So, there's no free lunch. The thermistor in your Heatmiser stat probably cost a couple of cents. Now, you probably only need your Heatmiser stats to read approximately the same number to indicate approximately the same temperature (i.e. they don't need to be absolutely right) - so you may not care much about the accuracy of your measuring device - just that it is reasonably repeatable. Alternatively, as you only need to do this once - could you rent or borrow a more accurate thermometer? Alan 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted November 21, 2022 Share Posted November 21, 2022 4 minutes ago, gc100 said: Lots of those on amazon. I just presume given the price they are not going to be very accurate (or a least within 1 degree) There may be some with fake DS18b20s shipped with them, but you can swap that out for a genuine one. The display will only be reading of the probe, so should be as accurate as the probe. @TerryE and myself have both calibrated them independently, and via different method, and found the DS18b20 to be very good. 2 Link to comment Share on other sites More sharing options...
gc100 Posted November 22, 2022 Author Share Posted November 22, 2022 thanks guys Link to comment Share on other sites More sharing options...
TerryE Posted November 22, 2022 Share Posted November 22, 2022 I did a post on my calibration process. I just bought 20 generics and put 2 batches of 10 DS18B20s in a bowl of hot water wrapped in a towel and ran a small logger to take the temps every couple of mins overnight and until it cooled down. I then did a curve fit. A couple of them had a gradient that was off the average by about ½°C over the ~30°C range so I chucked those. I noted the offset from average for each and my logger offset the reading accordingly. This meant that they were all consistent to within the 0.125°C tolerance. 2 Link to comment Share on other sites More sharing options...
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