Hi @LéoC
Help links for using Snowflake in Zapier: https://zapier.com/apps/snowflake/integrations#help
Hi and welcome to the community, @LéoC! 
There isn’t a specific limit for the number of fields or bytes as far as I can tell. It’s likely the 30-second limit for queries to run that’s causing the “504 Gateway Time-out” error here, if it’s taking too long for the query to complete.
That said, I saw that you also reached out to our Support team and seem to have found the answer through your own testing. Sharing your findings here in case they help others with the same question:
“I did some tests and found out that for the exact same query with 17 columns,
- LIMIT 400 rows works instantly
- but LIMIT 500 I'm receiving an error message
It looks like the limit must be between 6800 & 8500 cells”
Also worth noting that if you reduce the number of columns and increase the number of rows, it might still be possible to keep the query within the 30-second time limit and avoid the error. However, the query may still occasionally time out if Snowflake’s servers are experiencing high loads when the Zap runs. In those cases, you can try replaying any errored Zap runs a bit later and they should go through successfully once the server load has decreased.
Hope this helps—please mark it as the best answer if it did, and let us know if we can help with anything else. Until then, happy Zapping! 

Thank you very much,
Indeed I did some additional tests later on and found out in my case, with the exact same SQL query in Zapier, which has 17 columns,
- LIMIT 400 rows works instantly
- but LIMIT 500 I'm receiving a “504 Gateway Time-out” error message
- It looks like the limit must be between 6800 & 8500 cells
You’re very welcome, @LéoC! Thank you so much for confirming that. 
Seems like you’re all set for now but do reach back out if we can help with anything else. Hope you have a great week! 