Hello, I'm about to post a question to sStack eExchange.

I deleted the equations and most of the formatting to make it more readable.

I'm trying to design a growing box that will keepmaintain a stable temperature for germination of seeds.

“Germination of seeds” is not technically wrong but I would say “seed germination”

Another way to say this: “I’m trying to design a growing box that will keep the temperature stable (enough) for seed germination.”

I'm not sure what the isonsulation of the box will be, but I'm considering either a plastic box, or an old refrigerator.

The target temperature is 30°C (86°F).

I need to choose the right heating element, and determine what power supply to use for that heating element.

I've already done some calculations for reaching this goal.

I can’t put my finger on what it is, but this sentence reads a little strange to me. You get your point across though so I think it is fine.

I might instead say “I’ve already done some calculations to work towards this goal.”

First of all, I need to determine how much power is required to heat up the box to the target temperature.

Let's assume that the house temperature is 20°C and I want to heat it up to 30°C in 30 minutes.

You can also say “ambient temperature” to refer to the surroundings/environment

I used an equation from https://www.engineeringtoolbox.com/heat-up-energy-d_1055.html forto determininge the energy required to heat up a substance.

So the required power to heat up the box to the target temperature in 30 minutes is 6.7 watts.

For a more formal piece of writing, I would use a transition word like “Therefore” rather than “So”:

“Therefore, the required power...”

It is the first time I have calculated something like this.

You could also say “This is my first time doing a calculation like this.”

TPlease tell me if I made a mistake.

Your version is technically fine, but since you are posting on a forum I added the “please” for etiquette and to make the sentence a request rather than a command.

Does this mean that I need a heating element that consuminges 6.7 watts?

Am I on the right track, or is it complete nonsense what I wrote abovwhat I wrote above complete nonsense?

From what I know, the lessower the resistance, the greater the power.

But is it okay to use that smalla resistance that low in a circuit?

Hello, I'm about to post a question to sStack eExchange.

I'm trying to design a growing box that will keep a stable temperature for the germination of seeds.

I'm not sure what the isonsulation of the box will be, but I'm considering either a plastic box, or an old refrigerator.

The target temperature is 30°C (86°F).

I've already done some calculations forto reaching this goal.

First of all, I need to determine how much power is required to heat up the box to the target temperature.

Let's assume that the house temperature is 20°C and I want to heat it up to 30°C in 30 minutes.

So the required power to heat up the box to the target temperature in 30 minutes is 6.7 watts.

It isThis si the first time Ithat I have calculated something like this.

Am I on the right track, or is it complete nonsense what I wrote abovwhat I wrote above complete nonsense?

What would you recommend me as a power supply for this task?

If you have any other recommendation, feel free to share ithem.