Tankless water heaters – pros and cons? December 30, 2024 at 2:40 pm #42309 LindyParticipant Joined: Jan 2024 Posts: 80 Likes: 31LikeUp0::Pros – I get way more hot water than when I had a 7 gallon (I believe) tank. Cons – you will fill up your grey tank a lot faster as you have to let the water heat up for a bit first. But that may or may not be a concern to you.