Hi I was wondering if anyone has had any experience with Heat Recovery Units. These are units that attach to your HVAC and use the heat from that to provide hot water. Any help or comments would be greatly appreciated.

been using them in Florida for over 20 years

Use the search function to search all site forums on the word "desuper", or "desuper heater" and you'll find quite a bit of commentary & information on them.

In cooling-dominated climates it's an extremely cost-effective way to go, and still pretty-good in combination with with ground-source heat pumps in heating dominated climates.

Does anyone know of any reliable manufacturers of these units?

Check out AIRTAP HWHP