So I am having difficulty sprouting my chili seeds using the ENO method (wet cloth) because I believe the temperature at my place fluctuates too much between 16°C during the day when I'm working and 21°C when I'm home.

Now I was wondering what temperature the radiator gets when it is on and if it would - for example - be better idea to plant the seeds in soil, cover the container with foil and put those directly on the radiator to get the ground to warm up? Since I believe the ground will stay warm longer during the day and night when the radiator is off. And it won't get the direct heat from the radiator itself so it won't "cook" the seeds being on there directly.

What are your thoughts?

  • The temperature of a radiator depends on your hearth or boiler settings or type. For instance I have a HR type, quite new that is smart (which means it uses gradients instead of just on/off). It pumps water thru my radiators of 40-80 C (depending on delta, which is the difference between current and target temp).
    – benn
    Feb 16, 2018 at 12:02
  • Would the radiator get over 31°C? I have a non-stop flowing of water when it is turned on until the room gets to the desired temperature.
    – Tikkes
    Feb 16, 2018 at 12:23
  • With my system the temp would certainly get above 31C, 40 is minimum. I think your system will too, because heating your room with water of only 31C would take a long time.
    – benn
    Feb 16, 2018 at 12:32
  • 1
    No, it is ok the fluctuation of radiator. In nature day and night differences are higher, so your chili know not to worry. Feb 16, 2018 at 13:39
  • 2
    Guys, have you thought about either simply answering with a suggestion or taking this to Gardening & Landscaping Chat?
    – Stephie
    Feb 16, 2018 at 16:21

2 Answers 2


I don't know how techie you are, or whether you have techie friends that can help, but one solution which will serve you over a large number of years would be to use an inexpensive data logger. This would give you all the data you need and would eliminate any concerns. Here in Canada I am concerned about my back room waterworks freezing in winter and the woodstove overheating, so I have a small microcomputer board with temperature sensors attached using twisted pair telephone wire. The advantage of this approach is that I can monitor 3 separate locations simultaneously with one little USB board, can move the sensors around as required to monitor different things depending on the season, and all the data is saved to a database so I have a good history of readings.

Once you have your sensor recording you can fix it to the radiator, or put it somewhere that you believe would register the right readings and sit back and wait for results to be recorded while you are out. You can also record light levels, humidity and so on.

To do some more reading on this possibility, use search terms like "arduino, raspberry pi, temperature sensor, data logging, LM 35" which will get you started. There are lots of little articles about how to set things up.


Nobody online knows how hot your radiator will get, let alone the amount of contact with the pots, or airflow in the room, and every other detail needed to determine the peak temperature. Stick a thermometer in a similar pot of soil put it over the radiator and check the temperature about every 30 minutes while you are home for a few days. A cover to keep in moisture will also raise the soil temperature a few degrees. If the peak stays below 35c then it will not harm the seed and is suitable, the ideal temperature mean for chile germination is 25-30c. Low temperatures for a few hours will not harm the seeds but will slow them down. They essentially accumulate degree-hours from 15c, when they have enough accumulated degree-hours they germinate. 16c for one hour accumulates one degree hour, 21c for one hour is 6 degree hours.(degree-hour accumulation applies to reasonable temperatures; anything over 30c is counted as 30c and time over 40c is damaging.) You may also see the term degree-days it is the same idea but uses the 24 hour average temp and days rather than hours, much like measuring in Km instead of meters.

Some seeds actually germinate better with daily fluctuation of about 5c, as it emulates sun hitting the dirt in the day and the seed wouldn't want to grow in shade.

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