I am looking to add a 2 person hot tub on my deck. My deck is made of all 2x6 material 12" on center floor joist, with 4x4 post and a 2x12 support band. It sits about 2 feet off the ground. The weight of the tub full would be about 2300 pounds. Will my deck hold this or will I have to add support?
To answer correctly, you would need to show or say the dimensions of the tub and the distance from the existing 4x4 supports. Don't forget the additional weight of 2 people. If it is near a support post, you will be fine. I would play it safe and add a post, secured to a 2x6 directly under the tub.
A standard 4x4 doug fir post can support roughly 7500# directly on top of it. But I like to use a safety factor of 3, because I don't like riding on the edge, so lets call it 2500#. If you have 4 of these posts, that's 10,000#. But that must also include the weight of the deck itself and anything else on the deck along with you and your other "man" and the tub and the water. 2300# for the tub would mean roughly only 250 gallons plus the pump, fiberglass shell, supports, pipes and insulation. So assuming the deck is not massive and you and your 2nd man are not behemoths, I think you are probably OK. If you are not sure, take it to a structural engineer, or (likely cheaper) put another post right under the tub.