legionaires and circulator pumps

[Thehardway]

Not sure where the best place to post this is as radiant heat and OWB's seem to spill over on this forum from the wood burning forum quite often.  I recently bought an "instant hot water recirculating system" at Lowes made by Watts.  It consists of a little Grundfos circ pump that mounts directly on top of your hot water tank and a sendor valve which goes at the farthest hot/cold water tap.  It basically uses the cold water line as a return path to the water heater and circulates according to a user adjustable timer in 15 min. increments.  It says not to exceed 150F for the pump.

The setup works great with one minor hitch, the cold water side tap is now luke warm rather than icy cold like I was used to, and you have to cool off the pipes before it gets cold.  Since the cold water side is what we typically drink from, and our water is well water and not chlorinated, I was wondering if this should be a concern.  I know there are big debates over using open loop radiant systems because of the possibility of stagnant warm water breeding legionaires disease and I don't see how this is any different, especially if you set the timer to turn off for long periods at night.  Ironically they bill these as a method of preventing legionaires because the water does not cool off in the long pipe runs between use.  Hard to discern where marketing ends and concern begins.

I didn't see anything in the manual on it and I did a brief search on line and everything says to set your tank tstat at 145F to kill it, then the Energy star folks say to turn it down to 120 to save power.  How do ya win on this one and what are the real dangers?  I have my tank at 125F.  At 140F people are getting scalded which I see as a problem too.

I would like to place my radiant loop in this also and be able to circulate it all using one pump.  I suppose I will be an idiot risking life and limb doing this according to the plumbing experts and could be a genius according to the Mother Earth and DIY folks.  Would like to hear some practical voices of experience on the topic.

BTW, my water heater is located in a mechanical building about 30' from the house, all lines are insulated individually and then slid inside a 4" corrugated PVC pipe which is buried between buildings.  The furthest spigot is about 60' from the mechanical building.  My plan would be to run to the faucets first and then use the cold water side Hot water return path as the supply to my  radiant manifold and allow the warm water to cycle through it on the way back to the hot water heater. A one way valve would prevent the cold water supply from pulling water out of the radiant loop.

I'l try and post a schematic when I can get to it.  Let me hear your thoughts and arguments...

[Holmes]

 My first thought is the type of pipe you have for the radiant. Is it allowed for potable water? Does it have an oxygen diffusion barrier that is acceptable to potable water.  If it regular pex it does not have an oxygen diff. barrier.

I  was told that keeping hot water at 122 degrees was good enough to not have to worry about legionnaires. By Viessmann

[Thehardway]

ThermaPEX oxygen barrier pipe was used in floors in case i ever decided to move to a boiler.  Standard PEX and copper used for plumbing.

[Holmes]

I would check with thermaPEx and see if that pipe can be used for potable water.  I run my water heaters a little low 118 degrees but I do  turn them up to 140 twice a year.

[SPIKER]

I do think the legionnaires requires more of  warm moist environment, stagnant type water.   I dont think Flowing water under pressure (IE in the pipes) would be a suitable environment.


Mark

[barbender]

Any of the oxygen barrier pex I have seen was for non-potable use only. My heating system will be set up with a water to water plate exchanger to separate the heating side from the potable side, my hot water potable supply is set up with a send and return. I don't understand how the cold water is incorporated as a return, does it have a one way check valve?

[Thehardway]

It has a "sensor valve" which forms a loop at the end on the hot and cold supply lines.  The hot water returns back to the hot water heater through the cold water inlet under the pressure and draw of the circulator pump. The advantage of a an open loop lies in the ability to omit the heat exchanger which is a point of efficiency loss. It also can reduce the need for multiple pumps

[Randy88]

I almost died of legionaires decades ago, that I got while on a train ride from someone who was sick, several of us ended up with and more died from it than lived, I was one of the lucky one's you could say.  I'll try to be politically correct in saying this, but doubtful it'll come out right, so have patience with me.   

I'm not sure I fully understand what your doing, but if I understand it right, you need to redo your plumbing and install more pumps, keep your water supply and returns separate and the heat side separate from the drinking side.    A lot of pathogens can live in warm temps, you need to listen to plumbers on how to install things, obey building codes and have your water tested yearly, at several locations throughout the system, from the well to the taps and in between is my advice. 

I'd even think hard on a chlorine treatment system if your water tests came back not up to snuff every year, but that's just me, I'd also run far hotter hot water temps than what you've been told to do, even my kids never had issues with scalding, as they say kids can and do learn, but do as you wish. 

[Thehardway]

Randy,

I hear what you are saying and this is the very reason why I ask the question.  Why do many plumbing codes prohibit "open loop" radiant systems that combine radiant system water with potable water but allow for potable hot water recirculating pumps that basically do the same exact thing using cold loop for return and on a timer?  This is confusing to me. Either recirculating water in the potable system is safe or it is not, right?  All I can figure is that they are making allowance because of influx of fresh water on cold side reduces chances of stagnation?

I chlorinate my pipes about once every 2 months to kill iron bacteria in the system which cause a slight odor.  I then thoroughly flush it. I don't like to drink water with chlorine or use it on my skin. I know millions of people do but I prefer not to.  I also prefer not to have flouride in my water.

I have upped my tank temp to 135/140 while I am testing this all out.

Strange but I have a cold water pressure reduction at the farthest tap, (The one the valve is installed on), not sure what is causing this, perhaps some air trapped in the line.

[Randy88]

Lets back up a step and look at it from a distance if possible, if I understand you right, your combining hot water from an outside source or heating your in floor heat and drinking that water and your asking how that is different than heating plain hot water and circulating that back to your water heater if I'm not lost in this discussion.   

First lets say in most drinkable water situations, your not drinking the hot water portion of heating water from the water heater, next most don't recirculate the hot water from a cold pipe back to the water heater, now some do to speed up the water in the tap to get it hotter quicker, but most of those systems also have continuous circulation in hopes of eliminating the problem of bacteria even starting to grow in the first place.   I'm not sure how your planning on doing it or the reasons why, but in most houses cold water stays cold and hot water is run hot enough to kill most anything that would get into the system, you have to remember before anything can grow, something has to be in the system first, just because it has a nice enviroment to grow doesn't mean it will if the bacteria isn't present to grow, it won't.   

By introducing non potable water into the equation, or lines or systems that are not potable into that equation, your the one introducing the ability for bacteria to grow in the first place.    This is why I recommend a water test to know where you stand today, if you have bacteria in your water, you should take precautions and change things to prevent problems from happening, if your water is good and has no issues, its up to you to keep them out of the system and one way is to keep hot water temps up, potable water separate from non potable and those two systems completely isolated from each other.     

As for saving the earth people and saving energy by turning down your hot water thermostats, that's a personal choice, my water is hot, we use a sidearm on the water heater to isolate the two systems and I run hot water in the faucets till its hot before using hot water, I also mix the hot water at the end used faucet to help eliminate problems at all and I don't drink hot water, we heat cold water if we need to drink hot water in coffee or tea or whatever we need it for.    If my owb has a water temp of 150-180 so does my hot water in the house.     If you have bacteria in your system already, you need to know what type your dealing with in order to treat your system effectively and eliminate health problems, most systems have something in them, just not high enough levels to cause problems at any time during the year, its another reason why I recommend water testing and do it at several intervals throughout the year due to changing factors of weather and temps cause different problems.   

[Thehardway]

I guess a diagram would be very helpful.  Here is the hot water recirculating system diagram as it is supposed to be installed according to manufacturer. I see no difference whatsoever between this and a typical open loop radiant setup which is supposedly ill advised.   




The "Sensing Valve" is basically a thermostatic valve, factory set to open whenever temp drops below 98F.  It allows water to pass from the hot water supply side to the cold water supply which under the pressure of the circulator pump becomes a return path to the hot water heater.  Energy savings is potentially derived by recirculating 98F water through the pipes for re-heating rather than allowing cold makeup water into the tank by running hot water tap until it gets warm.  The second diagram shows the recirc. path when the valve opens.  It seems to me that 98F is a little low but there is no way to adjust setpoint.

We do not drink from the hot water side directly.  The cold water however becomes "hot" when you have not been running cold water.


If the timer shuts off the recirculating pump, the 98F water stays in the cold water pipe until flushed out by opening the cold tap or until the recirc. comes back on.  All water in the system is considered potable, there is no intermingling with chemically treated water or DWV water.  All water is supplied from freshwater well.

The third diagram shows how the system could potentially be used to circulate the 98F water through the radiant slab before it returns to the hot water heater. In radiant heating mode, V1 is placed in the closed position and V1,V2 are opened forcing the water through the loop on its return back to the hot water heater.  Any time cold water is run, the radiant tubing is flushed with fresh cold water, eliminating possibility of stagnation in the radiant pipes.  To remove the radiant loop, V1 is opened and V2,V3, are closed, isolating the loop.  when loop is initially placed in service, it is flushed/chlorinated to remove any possible bacteria from stagnation. loop
  


Hopefully this clarifies the muddy water situation I have made. :D

[Randy88]

I'm no plumbing expert by any means, just enough to be dangerous and do my own, but in your first two diagrams, if it were me, I'd make a third loop back to the tank off the hot side, forget the valve your thinking about and pump,  keep the hot water circulating and keep your cold water completely separate and cold at all times, put it back into the bottom of the water heater and it will create its own circulation, no different than a side arm heat exchanger.   

Your third diagram is the disturbing one to me, anytime your talking in floor or heating another source, besides your hot water, I'd have a separate heating source, either a separate hot water heater feed off a side arm or use a plate heat exchanger and keep the water and heat sources separate.   I've never seen anyone do something like that or even recommend it via your diagram to run the infloor heat off the cold water return being heated to only that 100 degree's, if I understand the diagram right, your throttling valve you'd have on your infloor heat your putting at your faucets to mix the cold water to back your temps down to run under the cement.   

Again this is just me, but my infloor heat and domestic water are separate at all times.    The hot water is kept hot via a return line to the bottom of the water heater and my cold water side is always cold and there's a backflow valve in the cold line at the water heater to prevent hot water from backing up into the cold line at all.    I'd have to check and each state is different but your third diagram might not even pass building/plumbing codes in my state.    Not sure I helped at all, but as they say, if your concerned even in the slightest, consult local professionals and check on criteria in your area, not from the sales people trying to make a sale.   Best of luck

[Thehardway]

So, this weekend I experimented with my circulator pump and radiant floor heat.  I thought through some of the recommendations here and I took a few suggestions and turned things around a bit.  The results seem to work well, almost too well.  My wife claims it is too hot in the house and she can't sleep although she does like the feel of the warm floors.  She says it makes the tile flooring seem softer on her feet.

So here is what I ended up with in this experiment phase.

 

The Water heater is set at approx 135F

Water temps as read with infrared thermometer on outside of PEX at manifold is 125F entering the loops.

I set the circ. pump on continuous for initial testing. I started at about 10:00 Sat morning.  I opened loops one at a time to purge air and limit the influx of cold water into the Water Heater. By evening, I had all loops on with floor temps ranging from 78F in the living room to 91F in the bathroom.  The manifold is located under the tub in the bathroom and all loops leave the bathroom so it gets warmer in there than elsewhere.  This was somewhat by design as the bathroom should be kept warmer than say the bedroom but as it works out, I get enough residual bleed off that I can leave the Bathroom loop in the off position.  By Sun morning all floors were in excess of 85F.  We were very warm in the house.  Indoor air temp was 74F.  This feels very warm when there is no draft or air movement.

Flow is as follows.  Radiant loops are branched off of the hot and cold inlet/outlet of the water heater,  The circulating pump is placed in continuous mode.  It supplies hot water circulation to domestic hot water taps if temp at the thermostatic valve on farthest tap drops under 95F.  If the valve is satisfied, circulation pump pressure is diverted to the radiant loop.  The Bath loop is closed because of bleed over from other zones.  Balancing can be done using the individual valves to limit flow.  I turned the system off last night and floor temps this AM were uniformly 76-77F. 

When I left for work this AM, I set the circ. pump in Timer mode with timer set for 15 min on, followed by 45min off every hour.  I figure this should maintain roughly 78-80F in floors which feels comfortable on feet without making rooms to hot.

All water in the radiant loops circulates through the hot water heater.  No water is allowed to stagnate for more than 45min before it goes through re-heat to 135F. 

Based on the results of this experiment I think the next phase will be to build a side arm exchanger for the hot water heater.  I will then purchase a second circulation pump and separate the domestic and radiant loops.  I would like to put a thermostat on the circulation pump that cuts it off if air temps inside reach 72F.  Other than this, timer can work to modulate heat on and off. 

Conclusion of experiment is that a single circulating pump can be used to do both radiant and domestic hot water re-circ. duty as long as water is not allowed to stagnate at any one place in the system.  It is not optimal but would work in emergency situation or if budget was extremely limited.  I am impressed with the simplicity and low cost of this system.  With a house that breathed a little more than mine it would probably work well.

[WmFritz]

That's an interesting diagram.
I'm curious about the BTU output on your heater and length's of your 5 loops. I'd assume no more then 1500 ft total.

I've been using a tankless heater in our house for around 10 years now and the only downside I've found is a little more water is wasted waiting for that hot water to get there.  I'm also using tankless at our cabin for radiant and dhw. But, the cabin systems are separate, so I can run glycol in the radiant floors.

[Thehardway]

My water heater is a dual 5500W element with 80gal. storage tank.  All loops were limited to 300 ft. so yes, 1500' total. The Aux loop was intended to be a fan coil loop for up stairs but it is not needed so it is turned off. Yesterday and last night I ran the 15 min. on 45Min off cycle.  Air temps in the house are slowly rising. It was a little too warm for sleeping last night and we ended up opening the windows for awhile in the middle of the night.   Floor temps are not quite as even as I would like to see.  Beginning of loops is hotter and end much cooler.  I think I'm going to change it up a bit tonight and go to 30min. on 1.5 hr off.  This should provide more even temps but give a longer cool down so not so much overall gain.