Flushing removes stagnant water and decreases concentration of bacteria just as it would in a hot water tank or a seldom used leg of a domestic water system. The same thing you should be doing with air conditioning systems or humidifiers .
Combine that with periodic raising of the water temp. of the system and you kill off a significant portion of the bacteria.

I am controlling not eliminating Legionnaire bacteria. The only way to kill it ( in the home situation) is to have the water at above 168 at all times. That is an impossibility. Every time you shower you add cooler water to the mix and recontaminate the water you just disinfected. Legionnaire is present in almost all water and the best we can hope is to control the level of contamination.

I should also note that we chlorinate our entire system including radiant once a year. We are on a well system and if we don't do this at least once a year the cold water becomes undrinkable and the fixtures stained.

You can kill it in the pluming with 160F purging flush, (hospital decontamination style) without 168F water all the time. 125F-130F storage is enough to keep it from getting started, and 140F is a reliable-kill (but not instant-kill.)

Recontamination at the mixing valve is (nearly) a non-issue, since contamination from the cold side is small, and the stagnation temp of the distribution plumbing or shower heads is lower than fast-colonization temps- it's room temp- the same temp as the cold-distribution. It's only the heating loops that stay in the wrong temp range for extended periods of time and have the elevated risk, and simple flushing will NOT dislodge active colonies on the pipe walls.

What temps do you hit (and for how long) on the "...periodic raising of the water temp. of the system..."??? If those pipes aren't hitting at least 140F, you're not doing much.

Seems like a lot of headache just to be able to run it open-loop. Running 100' of PEX in a heated slab for DHW pre-heat is one thing- it's 100% purged multiple times/day, every day, even if it occasionally spends more than half a day at temps "in the zone". But for potable water in 1000s of feet of heating water tubing it's another story.

My apologies for not replying sooner but I have other business and little spare time. You are all missing the point. The title of this thread is "Using tankless water heaters for radiant heating". It is interesting that those in the business of designing/installing radiant systems have disregarded the subject matter and sidetracked this forum into a rant about 'stagnant water in open loop systems'. I just wanted folks to know that it is quite do-able. I don't make any claims about longevity. I never claimed that open loop was the way to go - I just happen to use such a system. For Petes' sake, use a closed loop system if you are concerned about stagnant water! Whatever. But a regular $250 electric tankless will get the job done. I have proven it to myself. You don't necessarily need to spend the cash for a pricey boiler. If you have the money and are skeptical, then buy the boiler.  But if you don't have that kind of cash, are a hands-on person and are willing/able to experiment, you'll find what I said to be so.

Eric: You said "Let me get this straight. You have a cabin (vacation home) that you leave unattended for long periods of time in a freezing climate".  You have misread something. And it is irrelevant.

Rob: You said "You can get a heating rated electric unit for not much over $1k if you like."  I don't like!    At least you change things up by suggesting that you're still not convinced I don't work for Titan. Whatever you choose to believe you'll believe, I suppose. Maybe I should be working for them!  I see good and I see bad feedback on this brand, but I suspect the bad is from ignorance, faulty installation or skeptics, because mine work fine. They may quit tomorrow, but have done great so far.


Dan, you have proven my point - the cheapest comparable (11.5kw) boiler on the site you suggested was $1355 wholesale!  

Jmagill: Bravo, my hat is off to you. You, with the patience and fortitude to defend the qualities of the open loop system. I'm not sure that argument is worthy the effort; skeptics will always be skeptical. Best you should expect is a stalemate.

Exactly so Dana,

A subtle but important distinction.

The radiant floor "open system" is often confused with a close-coupled water heater with fan coil. Where one is typically operated with water temperatures above 120°F with tank temperatures higher still, the other may always operate in the Legionella "sweet spot".

Some skepticism is in order when common water heater temperatures are thrown about as the "perfect" environment for Legionella while the power company keeps telling us to "turn it down". But radiant floors and potable water don't mix well.

Still alive and kicking in Minnesota!

 “We plumbed the radiant heating loop of our vacation cabin to the domestic hot water, making an open loop system”.
  “They are used in a myriad of successful applications. And as far as cost, you don’t mention the added costs of a closed loop system (besides the boiler) such as a heat exchanger, antifreeze, expansion tank, etc. And please tell us where you can purchase a suitable (warranted) electric boiler for less that $500 – we all would like to know”.
 
Dave, these are 2 quotes directly from YOU. In the first you call it a vacation cabin, in the second you talk about using antifreeze, which would only be relevant in a heating climate. I assumed that a vacation home is not right next to your regular home and you are not going there every day or so to check on it.
 
Here is what I wrote:  “Let me get this straight. You have a cabin (vacation home) that you leave unattended for long periods of time in a freezing climate. You do your own plumbing, so the only costs involved are parts. You already have the radiant installed, so you are looking at the costs of the electric boiler, 1 expansion tank, a pressure reducer, and air separator . buy a slant fin electric boiler for 1200$, it comes with the controls built in and an air separator, you are looking at 1500$ to make this work and do it right. Not the end of the world”

Based on your quotes and seeing first hand the damage running water from burst pipes do in unattended vacation homes in cold climates, I thought your plan of a half-assed heating system did not make much sense. There is a good reason boilers are more expensive then DHW systems. First the duty cycle is a lot greater in a boiler, second, if your DHW system breaks, you take a cold shower, if your heating system fails and you are not around to notice(vacation home), your house freezes and lots of things break. An extra 5-800$ to do it correctly vs 30,000 for mold remediation, new insulation, sheetrock, floors, etc when you have water flowing in your house for 4-5 days because the heating system crashed. That is my point.

This forum is all about exchange of ideas, but when someone proposes an idea that you think is not smart or safe you kind of have to say so.
You may have different ideas and that is fine also. I sincerely hope your system works well and you have no problems with it.
Good Luck
 Eric

Hi Eric, I am not the sharpest tack in the box after a long day. I realized why you would assume it was a freezing climate early this morning, but you beat me to the edit. I mentioned that while considering the added costs one might encounter with a closed loop system, so that was quite a fair assumption. And yes, a boiler should give longer service. But if you use the radiant system relatively sparingly, you can get by with a cheaper alternative just fine.

Dave,
Beg to differ, I have agreed that using a tankless water heater is ok, and provided a link to a electric tankless unit under $500.00 that is approved for heating. What I do not agree with as do the others here is the combined use system, domestic H20 and Heating together with the same appliance and no heat exchanger. This is what is referred to open loop system.
Heat on,
Dan

Dave, in my experience when people just pop out of the blue with long posts that are not asking questions, they are usually paid to do so. Maybe you are, maybe you aren't, doesn't really matter. I'm quite happy chewing on the merits or lack thereof of your system, even if it were a pretend system, as we have seen show up on these boards many times. If I am wrong, so be it, but please understand I've played that game many times and you are definitely "fitting the profile" here.

back to merits:

If system failure is no concern to you, i.e. you can just run the unit until it dies and not care, then go nuts. I don't regard that as an acceptable design parameter for 99.99% of systems, but some people just don't care and aren't in a freeze risk situation and so be it. the "wild outdoorsmen" out there can tinker and replace units all day if that's a hobby of theirs. Have fun with that.

But you already bought two units, and you'll be into it for more before long running non-heating units as heaters. Instead, you could have gotten a unit rated to actually do what you are trying to do, with a warranty, and be relatively sure you'd have a reliable system, and you could have done it for not that much more in the end. If YOU think you took a wise path forward, more power to you. I don't. You've made a mistake.

if the best you have is that "using it sparingly" might extend the life of the units you chose, well that's great, congrats on installing a system you can't really *use*. If you're going to use the system that sparingly, why did you do radiant at all? you wasted a bunch of money in that case. a few panel radiators would have saved much more than $500 I bet, though you don't say how big the cabin is, with the heat load you are apparently servicing it must be regular house sized.



Doing it open loop is, plainly, stupid. all the discussion about it in this thread is often part of the discussion with using DHW sources for heating, and is well placed in this thread, whether you think it's "missing the point" or not. Focused people like Jmcgill may be able to minimize risks for themselves, but you have said *nothing* that indicates that you have even reduced any risks involved with open systems on this. I know you *think* you have, but you haven't. You've taken feel good steps that actually don't address the issue at all, and nothing you do will address water quality issues.

You may be taken aback at being told you did the wrong thing, and you made bad choices here. but they are plain facts. I only hope, in all seriousness, that the worst that happens is you have a few no heat situations. That would be the best case scenario. *please at least install a heat exchanger or separate the units to dedicate one for heating only*.

Dan, my sincere apologies for the big misunderstanding. I thought you meant the Thermolec boilers, as the American Heat tankless ad didn't say anything about using them in a radiant heat system. The ADK unit is made similarly to the units I have here, but I like their stainless heat exchanger (while these are brass?) and the 1/2" full flow (I had to enlarge the outlet orifices in these out to get adequate flow). If these are warranted for use in radiant applications they are clearly a better choice for not much more money as you said, and I will certainly keep them in mind in the event these cheaper units fail (I bet you're thinking 'when' they fail). Thank you for clarifying this and taking the time to steer me to the right. I wasn't aware of this brand. This is perhaps why you are in the business and I am not. 

Feeling quite small, Dave

Wow Dave! Bet you weren't expecting this kind of response! I sure wasn't when I saw the tread title.

Last year we started a project to see how economically we could construct a very energy efficient shop type building. Our target goal was less than $50/sq ft and we are at the $35 mark. Part of keeping the costs down was to use radiant heat and as cheap of a heat source as we could. We chose a very low cost instantaneous water heater for our first season. Because this is a test building, we data logged the outside air, inside air temperatures, humidity, system run time, pump on/off cycles and run time, and current to the heater.

What we found was the flow rate on the system was low due to restrictiveness of the heater design, the heat would run close to 100 percent of the time that the system called for heat. The current varied between 35 and 50 amps so we assume there was some form of modulation. (We got zero cooperation or information from the manufacturer.) The heater did survive the winter and kept the space within 2 deg plus or minus of the 60 deg f set point. But we did notice on our post season inspection that the terminal block on the heater showed signs of charring. The assumption is the continuous load was a little too much for the hardware. This year, we will find a heater that is less restrictive and rated for hydronic heating.
If yours is not rated for heating, better keep a close eye on it.

Well if you've read this thread you know that Dan indicated that American Heats' units are full flow and rated for radiant heating, and at a good price. I will be keeping and eye on things of course. I'm interested in your statement "the heat would run close to 100 percent of the time that the system called for heat". Isn't that what it's supposed to do?

Yes, but the problem was that at night the system would call for heat for hours on end. Somebody correct me if I'm wrong, but a heater designed/rated for heating is capable of running for hours with out damage. One designed for hot water is not typicaly going to run for hours on end and might not be expected to do so. A higher quality IWH should be OK, but I'm not sure I want to risk another winter with the cheap one.

arcamm is RIGHT!

Well done old man.

Dan, I thought I would give the 'American Tankless' water heater that you suggested serious consideration, but see they are no longer listed on the site: http://www.blueridgecompany.com/rad...er-heaters . Wonder what happened? Can you suggest another (12kw) that would be suitable for radiant heating? Dave

for low flow situations, we like the Seisco SH units.

Thanks for the info Rob. Your suggestion (Seisco) turned up a lot of bad reviews (sorry) but it led me to Steibel Eltron, which led me to their radiant heating model, the Hydro Shark. They are being sold by a greenhouse supply company I have done business with in the past, and at a reasonable price. I guess the 'American Tankless' brand that Dan suggested earlier didn't work out for whatever reason, as Blue Ridge stopped offering them.  Again, thanks for your help.

I was waiting for the info on the American Heat, but it never showed up on the website. I contacted the manufacturer and found out it was about the same restriction as the Hydro Shark. It started getting cold so we went with a Thermolec. So far it's been great. Flow rates are up on the system and with it's built in pump control and OAT reset, the panel build was much easier.

We have yet to have any problems with the Seisco units. I've heard some murmurs in the past but in the last couple of years we've been working with the units they have all performed flawlessly.

Thermolec is a good choice too. Spendier, but I really like them on higher flow systems to avoid the need to go primary/secondary, that extra savings makes the unit even more attractive. I'm not very impressed with their "outdoor reset" though...

Here we have a critical difference between the layman and the professional.

As I have spent a good bit of time "with" Rob and I don't doubt his veracity, which leads me to believe that the "boiler reviews" you mention are from the DIY crowd. Hardly a valid resource.

The professional on the other hand usually has a long and stable relationship with his distributor and the distributor with his manufacture.

My boiler suppliers for instance sell hundreds of boilers to my dozens and can give me good advice based on professional standards. By contrast, the typical DIY boiler installer will buy one boiler in his lifetime.

I do not take online boiler reviews seriously unless found on a professional (usually exclusive) sites.

Yes, checking back I can see both situations. They were older posts, and appeared to be mostly DIY'ers with the complaints. Looking further into it, Steibel has been in the business a long time and are still going strong.   Again, thanks for the info guys - I'm learning a lot here.