Clarification on Ethereum gas limit

Question

I know this one has been asked many times before and I think I get it, but I just need a little more clarification.

At the moment, https://ethgasstation.info shows the following gas prices

Safe Low 1 gwei
Standard 5 gwei
Fast     8 gwei

So, I get that those are the recommended gas prices depending on how fast I want my transaction to be processed.

My question is regarding the gas limit. On this post, Questions about some details on Ethereum transfers and Gwei it mentions that a simple transfer will always be 21,000 gas but then later says gas limit is 21,000 + additional gas needed by the contract.

All I want to do is move some ETH from my wallet to an exchange, so does a simple transfer need any additional gas or is the original statement that 21,000 is enough true?

Am I right in thinking that if I use a limit of 21,000 at a price of 1 gwei to move ETH from my wallet to an exchange, it should go through in around 30 minutes?

The thing that concerns me about the limit is, if I don't specify enough, the transaction won't complete and I'll just lose the gas I've paid.

Thanks for any advice you can give.

Answer 1

You should probably use more than 21,000 gas, as the exchange wallets are usually smart contracts. They execute code, like logging an event, so the exchange gets notified whenever you deposit ether. If there's not enough gas, you'll lose all of it, without any result. If there's too much gas, however, you'll get the excess back.

As for the gas price: 1 gwei should be fine, but it won't be a fast transaction