Heizungsbau question - why is the thermometer outdoor in modern residential properties?

15 posts in this topic

Not idea if this is only in Germany, but I guess it is not.

Knowing nothing about heating of buildings, I would have imagined the thermometer has to be inside, not outside.

So whenever the measured temperature (indoor!) drops below the preset desired value, the gas valve (or whatever equivalent) opens, and viceversa.

 

Instead, all modern houses I looked at, all in Germany, have the thermometer outside, not inside.  

Sure there's got to be an engineering reason for this...

 

The best guess I could come up with, and it's still not a good guess, is that this way the heating starts just before the indoor temperature drops, so eventually the temperature is more stable throughout the day and it should be more comfortable.

This relaxes the demand for the power/size of the heating system, gas boiler or whatever, (takes the same energy though), and construction/installation cheaper (not the running or energy consumption, though).

But this of course ignores what else goes on inside the building (oven running like mad, crazy wild party with zillion of guests, camin fire...)

 

Can anyone explain?

I'm just a curious nerd, thanks

1

Share this post


Link to post
Share on other sites

Our house, built in the 60, also has the thermostat outside.  The only thing that I can think of is that it ensures that the pipes get heated when there is a frost.  I find it strange as my heating comes on sometimes when I don't want it to and vice versa.

0

Share this post


Link to post
Share on other sites
1 hour ago, Gambatte said:

Not idea if this is only in Germany, but I guess it is not.

Knowing nothing about heating of buildings, I would have imagined the thermometer has to be inside, not outside.

So whenever the measured temperature (indoor!) drops below the preset desired value, the gas valve (or whatever equivalent) opens, and viceversa.

 

Instead, all modern houses I looked at, all in Germany, have the thermometer outside, not inside.  

Sure there's got to be an engineering reason for this...

Nope, not an engineering reason, it's one of these rules that curtail your right to heat your house because of ecological reasons.

 

These "Außenfühler" (outside thermostat) are mandatory, even if you change something major in an existing heating situation, the plumber is obliged by law to put one in (well, get an electrician to put one in), this law is enforced by the district chimney sweep doing his inspection after the "major" repair.

You would then have to cut/disconnect the electrical wire to that Außenfühler, to then be able to return to the default that you had before this major repair, i.e. that if you turn on the heating through raising the temperature at your inside thermostat (usually located in the living room), that it then actually heats.

With a connected "Außenfühler", you no matter to what temperature you put the inside thermostat, if the "Außerfühler" thinks that the outside temperature is too high for you to be "allowed" to heat your own house, the heating won't turn on: https://www-viessmann--community-com.translate.goog/t5/Sonstige-Produkte/Aussenfuehler-abstellen/td-p/182717?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en-US&_x_tr_pto=wapp

 

Sadly, their definition of a "major" repair is very restrictive, so if your inside thermostat should ever stop working or should you want to change it to a different room, they would refuse to simply do that and would oblige you to additionally install the Außenfühler.

In such cases, it helps to be an electrical engineer and able to do your own electrical installations, so that you can replace/install the inside thermostat yourself, using the simplest available model, which simply contains a bimetallic strip (yup, I checked, that is what it has inside) which will never ever stop working: https://www.idealo.de/preisvergleich/OffersOfProduct/763704_-vrk-121-vaillant.html

vaillant-vrk-121.jpg.c7544a3c996d0da9650

 

Did not have a good experience with the more complicated ones, the more electronics a device has, the less time it lasts.

vaillant-calormatic-332.jpg.c19d6915f7c3

0

Share this post


Link to post
Share on other sites

ok - where do I begin...

 

Our house, built 1963, has one thermometer outside, next to the garage door - used to determine, whether we need heating available at all (Heating is set to come on when outside temperature falls below 18°C).

 

Inside the house we have thermostats at every single radiator, allowing us to keep different rooms at different temperatures while heating is on. So, even though heating is currently on in the house (because it's cold outside), we have the radiators in the basement and the garage set to "Frostwächter" (so the pipes won't freeze). Living room is warmer than bedroom, or whatever we feel like - each room can be heated individually.

 

Now, if the outside thermometer would fail, heat may not come on when it's cold outside, or heat may not turn off, when it is warm outside.

0

Share this post


Link to post
Share on other sites
17 minutes ago, PandaMunich said:

With a connected "Außenfühler", you no matter to what temperature you put the inside thermostat, if the "Außerfühler" thinks that the outside temperature is too high for you to be "allowed" to heat your own house, the heating won't turn on

 

Very Interesting.

What is the threshold of this Außenfühler? In all the German properties I lived in, the indoor temperature could well be extremely high. I would say this Außenfühler is not really doing what is supposed to do...

 

0

Share this post


Link to post
Share on other sites
8 minutes ago, Gambatte said:

 

Very Interesting.

What is the threshold of this Außenfühler? In all the German properties I lived in, the indoor temperature could well be extremely high. I would say this Außenfühler is not really doing what is supposed to do...

 

the "Außenfühler" does exactly what you (or the owner of the house) tells it to do:

 

my parents (for example) have their heating system set to "always on" - Außenfühler turns heating system on if it is below 35°C outside.

You can program these things to do whatever you like (if you own the place).

 

The law for rental properties is more specific - heat has to be available whenever outside temperature falls below 18° C (or something like that)

0

Share this post


Link to post
Share on other sites

On the controller of our gas boiler, present modern house as well as former modern one, there's a magic settings that "pretends" to be the desired indoor temperature.

 

Problem 1:

to have a not-too-high indoor temperature, say 19C, I have to put this setting to a ridiculos low value, like 12C. I find hard to believe this is an offset on the thermometer scale.

 

Problem 2:

no matter what I set, the measured indoor temperature is far from constant, the warmer outdoor the warmer indoor, and viceversa. WTF??

0

Share this post


Link to post
Share on other sites
5 minutes ago, karin_brenig said:

the "Außenfühler" does exactly what you (or the owner of the house) tells it to do:

 

my parents (for example) have their heating system set to "always on" - Außenfühler turns heating system on if it is below 35°C outside.

You can program these things to do whatever you like (if you own the place).

 

Maybe you "can" but, if we believe Anda, and I do, the Außenfühler is there exactly to prevent you from doing this.

0

Share this post


Link to post
Share on other sites
12 minutes ago, Gambatte said:

 

Maybe you "can" but, if we believe Anda, and I do, the Außenfühler is there exactly to prevent you from doing this.

 

no, the Außenfühler simply measures a temperature and transmits the measurement to the control unit in the heating system. The control unit is the part of the system that "prevents" anything, or makes it happen. The owner of the house (or the person in charge of the heating system) has to program the controls accordingly, to make the desired behaviour happen. Has nothing to do with belief - just a matter of ownership.

Even the previous old furnace (built in 1996) in our house had a control unit mounted on the fron of it where you had to set the temperature range for "heat on" and "heat off". The controls were just not as easy to program as with our new system. (and it was less flexible/granular).

0

Share this post


Link to post
Share on other sites

 

1 hour ago, PandaMunich said:

With a connected "Außenfühler", you no matter to what temperature you put the inside thermostat, if the "Außerfühler" thinks that the outside temperature is too high for you to be "allowed" to heat your own house, the heating won't turn on:

 

31 minutes ago, karin_brenig said:

my parents (for example) have their heating system set to "always on" - Außenfühler turns heating system on if it is below 35°C outside.

You can program these things to do whatever you like (if you own the place)

 

0

Share this post


Link to post
Share on other sites

The Außenfühler is necessary to determine the temperature gradient, which in turn needs to be known in order to properly set the inlet temperature. The bigger the difference, the higher the inlet temperature needs to be.

1

Share this post


Link to post
Share on other sites
9 minutes ago, jeba said:

The Außenfühler is necessary to determine the temperature gradient, which in turn needs to be known in order to properly set the inlet temperature. The bigger the difference, the higher the inlet temperature needs to be.

This was exactly my opinion when I started the thread.

Some it doesn't work properly. Indoor temp never constant.

0

Share this post


Link to post
Share on other sites
11 hours ago, Gambatte said:

This was exactly my opinion when I started the thread.

Some it doesn't work properly. Indoor temp never constant.

A few degrees of variation won´t make much of a difference. However, it matters whether the outside temperature is +5°C or -20°C.

0

Share this post


Link to post
Share on other sites

For a system like ours (very well insulated house + low flow temp heat pump + concrete screed under floor heating) the system needs to know the outside temperature because if you waited until room x was "too cold" and then commanded the heating system to turn on and open valve x, the room would continue to cool down while the system pumped energy first into the concrete screed (which takes 24 hours to heat up) and only after a day or so would the ambient temperature in the room come up to the desired temperature. This is obviously not a very comfortable way to heat your home using these systems. If our heat pump knows about the fall in outside temperature immediately, it can respond by turning on and sending heat energy to the floors before they start to cool down. It leads to a very constant temperature in the house but the heating is switched on once in late autumn and off in early spring. You don't turn it on for a quick blast of heat like you do with a gas boiler + radiators. Heat pumps use a heat curve almost always based primarily on the external temperature.

2

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now