[Editor’s note: As far as I can tell, this comment was accidentally published as a new question (creating a new thread) when Richard Hugo really wanted to post the comment on a different page, in response to an existing thread. I think the comment belongs here: Hot water distribution.]

CL,
First, what I will agree with is that all existing homes require experience in determining the proper method for that home and Owner. What I understand is everyone is so stuck with the same ole way that we are comfortable with. The one story house two story or basement home works wonderful for gravity systems, one principle hot water rises and cold water is pulled by gravity. Just install the hot and return lines just above the ceiling and insulate with Attic insulation usually R-36 or 42 and this prevents heat loss. If any line breaks its a bad day but if your talking about freezing may I say install lines proper no problems if they freeze fire that plumber. Its has not been a problem and my Father starting installing this system in 1964 with no freeze problems. A pump usually circulates 4 GPM this will cause a water heater to fire up especially when the return line and feed are buried in dirt. gravity will move 2 to 2.5 GPH and properly insulated the returning water is about 95 degrees. I have no argument with the vacation and non use time, I would say pump passive system means no pump to maintain and hot water near all my fixtures when I use them 7 am or 2 am and preventing freeze conditions for the pipes. I use my personal utility bill water, sewage and energy fees, so do my customers. You can figure your normal wait for hot water and add up the gallons for your use and get local rates for utilities. Believe me doing this system will get you a whole lot of marriages to customers, so far since 1964 no divorces, yes problems that I had to work out in the patent office with the invention of the gravity thermal valve in 1998. All new homes need hot lines run above the slab and well insulated with or without circulation.

Thank you Have a blessed day
Richard