Heating my floor with my DHW recirculation line.

Just make sure that the Heat is still working even when it is 100 something outside and your AC is working..😕

As you can maybe appreciate and understand the formation of legionnaires is a risk with these kinds of setups.

Again….Not a big fan but Tekmar made a control that will purge the lines in order to prevent the formation legionnaires with this piping arrangement.

Seems like a clever idea to me.

Have you configured to runs when water temp drops below a set level?

I like it. My kind of engineering!

I'd feel better if you used a hx, probably could figure out a cleaver way to get the lower temp as a bonus.

My day job is designing/maintaining/installing AV systems and there is just a mass of unlabeled undressed wire behind my receiver, TV, and components and a few components sitting on the floor next to the cabinetry.

My recirculating system just uses a Taco 006 and an aquastat.

I had mentioned running it through a towel rack awhile back and quite a few people here seemed to think that was a terrible idea for some reason.

do you even actually catch it from DHW? It always seems to be from AC cooling towers or fountains spewing particles into the air

every day for 50 years my shower supply pipe gets up to 120 or so, then you know what? It cools off to about 70 degrees over the next x hours. Am I supposed to be scared?

Looking over @JohnNY 's design again, I don't see a reason for concern about Legionella from the floor return line. That recirculated water is going back to the hot water heater, which is kept at above 120. That will do any bacteria in there in in short order.

@WMno57 has some good comments about the elderly and immune history, though. The ability of our bodies to fight off various problems — or not — does decline with age, but is also influenced by our histories of exposure. I've read — and I'm sorry, I can't find the references — that farm kids tend to be healthier simply because they have been exposed to more "stuff" early in life. Then of course there is our individual genetic variation. I thank God, for instance, that I've been very healthy all my life — but I am a farm raised World War II brat. The only health problem I have was caused directly by the Covid 19 vaccine I more or less had to take (myocarditis leading to congestive heart failure)(it will make you healthy they said. It will prevent Covid they said. Wrong on both counts).

Hi, Looking into the future a bit, a concern about being self limiting comes up. Constant recirc may be needed in hospitals, but demand recirc is a better fit for residential application, and it is substantially more energy efficient. A wireless remote or motion sensor can activate the pump, getting you hot water by the time you need it. Floor heating isn't going to play nice with demand pumping, so the option of upgrading to the more efficient approach is no longer really an option. Aside from that, it looks like a nice two for one.

By the way, I recently did some testing for legionella in a 5+ year old solar tank fed with well water. The bottom of the tank, where I drew the test water from, rarely exceeds 110F. Test came back negative. I'm thinking a good immune system is the best defense, so nursing homes and hospitals absolutely need preventive measures, but homes with right-sized plumbing, maybe not so much. 🤔

Yours, Larry

We have been inadvertently doing this for years by not insulating DHW and recirc piping. You are just focusing it a bit more 😉. I think if this were mine, I would put some smart controls or a lighting timer on the pump so I could run it for a longer period when it is cold outside and reduce that amount of time you are heating and cooling at the same time in the summer.. I like the idea although I can't help thinking of Jeff Foxworthy 😂.

Good point! A friend of mine has a neighbor who just had Uponor pay for their DHW PEX (red and blue) replaced after it failed. I don't know the details, but they put a flow restrictor on the return line.

We have a good portion of methanol in it to keep it from freezing.

I personally feel it can be an issue and should be treated as such.

But I think it's pretty low on the list of concerns.