Just wanted to showcase my small scale HERMS I built recently. I live in NYC and brew 1 gallon recipes due to limited storage space. I started home brewing in early '00 but stopped because the 5 gallon batches were just too much beer to consume for a guy who lived alone and worked 60hrs a week.
I recently started brewing 1 gallon all-grain batches but they never really came out as good as my my partial-mashes I made about 18yrs ago. I decided to build something that would be more efficient and also not heat up the entire house using the gas stove. I know a lot of people think that 1 gallon brewing is a waste of time but I like the variety I can make and it's still so much cheaper than buying a $17 six pack of Sierra Nevada at the local deli. And we now have an 18mo old toddler running around so our beer consumption has dropped significantly.
I already owned an induction stove and sous vide circulator and wanted to upgrade my equipment to a HERMS without having too much extra equipment. Everything was purchased via Amazon and a couple Home Depot trips for about $300. I also built this with the intention of being able to upgrade the system down the road to do 2-3 gallon batches with only having to upgrade my brew kettle and some minor part purchases.
It took a couple brews to figure out a complete step by step process to brew but now that I have a system, the brewing process is so efficient. I also now use the HERMS coil as a wort chiller so that process now takes about 15min instead of a 40min ice bath.
Attached is my original blueprint for the system and a video of the complete brewery mashing an oatmeal porter.