What size breaker should be used for a dayton 3UG73 electric heater , wired for 240 volts

That unit can be wired for many different BTU levels and the BTU level that you choose will determine the breaker size. All of this should be included in your owners manual. See below

Heater, Utility - Electric Utility Heaters - Heating Equipment - HVACR : Grainger Industrial Supply

Yes my mistake , I forgot to include that it will be setup for 17,100 BTU (sorry)

It indisate in the owner manual maximum fuse (breaker) size 30 amp
I was wondering if this could use a 2 pole 20 amp or should I use the 30 amp 2 pole?

If the manual indicated a 30 amp for that heat selection then you use a 30 amp breaker. Real simple.

Thank you , I was just confused since it stated Maximum fuse size, I thoguht that possibly a 2 pole 20 would work as well ,
Forgive my lack of knowledge.

I did not say a 20 might not work but the use of a smaller breaker might cause it to trip. Make sure you use a minimum of # 10 wire for a short distance or #8 for longer distance. This should also be mentiuoned in your instructions. I have a smilar unit in the big garage and it is great to have heat for working on projects or cars. Good luck with your install.

I understand and thanks very much , in the owner manual it shows 17,100btu and the heater amps 20.9 so I think I will use the 30 amp 2 pole since 20.9 is greater than 20.
As I understand it , the unit will draw 20.9 so The 30 amp is the best option, after all it will only draw what it needs.

Yep and that 30 will trip on a short so you are covered. Now a 25 will also work but not necessary if wired as per the directions.

Yes , I saw that but I thought that was for 208 volts and would deliver only 12.799 btu's
I would prefer to not change any jumpers in the unit.
And again I love this site , I always get great help from you guys.
Thanks again

No problem. Enjoy the heat.

I have a dayton heater did not get a manual, not for sure what it is wired for