Using Tankless water heaters for radiant heating
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Dave EvelandUser is Offline
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22 Oct 2010 05:58 PM
I have discovered that using a tankless water heater for both domestic water and radiant heating is an efficient and inexpensive alternative to a boiler. Keep in mind there are no building codes in my rural part of the country, as there may be in your ‘neck of the woods’. And the cheaper tankless heaters are usually not recommended or warranted by most manufacturers to be used in a radiant heating system and it will probably void your warranty.

We plumbed the radiant heating loop of our vacation cabin to the domestic hot water, making an open loop system.  We don't usually drink water from the hot tap  - we heat it in the microwave or on the stove,  but I wouldn't see anything wrong with that either, as the water is not contaminated or otherwise unsuitable as in a closed loop system. It just goes through (a lot more) tubing and a stainless pump. Fresh water gets introduced into the loop every time we use the shower or DHW.

Originally I tried a 10 gallon tank type water heater, but it took a long time to heat the floor, even after I upgraded to a 220v/4.5kw element. So I decided to try a 7kw tankless 'point of use' heater, and was pleasantly surprised that it heated the cold concrete slab floor to 70 degrees in a reasonable time. The tank type water heater evidently was overwhelmed and thus could only provide tepid water, but the tankless heater put out a continuous supply of hot water which got the job done much sooner. The only drawback was if the floor heat was on, the domestic (tap) hot water would run just warm. This was OK, even for showers, but a dishwasher requires hot water (unless it has provisions for heating the water). And I prefer the hot tap to produce hot water.

So the following year I bought a larger but relatively inexpensive 'Titan' brand N120 tankless (11kw), and (after enlarging the outlet orifice to 1/4" - which will also  void your warranty) was happy to find it heated the floor in half the time while providing hot tap water!  At 95%+ efficiency, I don't see why this wouldn't be feasible in Northern climates as well, providing your floor or slab is properly insulated , and electric rates are reasonable (electricity here is only 7-8 cents a KWH so is in line with propane costs).  Once the initial heating cycle is completed, intermittent use keeps it warm. 

We were so happy with this arrangement that we have since converted our home as well. With the money saved from having to purchase higher priced ‘boilers’ we have purchased another backup heater for peace of mind. Time will tell how long they will last, but I suspect we’ll get a good return on our investment.   Dave



NRT.RobUser is Offline
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23 Oct 2010 11:26 AM
Electric tankless heaters are not the same as gas, first of all, so most of the conversations about tankless vs boilers do not apply if you are using electric.. However, Electric boilers are not typically *that* much more than electric tankless units. If you bought one in the first place instead of a tank, then 2 tankless heaters, you would have been ahead of the game. You're already "behind the game" on that, or at best on even ground.

If you're doing electric the best way is typically to use a separate on demand for hot water and a unit with a warranty for heating. There is a reason why some units are not rated for heating: it's a continuous demand instead of a very intermittent demand, and some units are built for it and some aren't. I suspect you'll fry a unit not rated for heating in a fairly short time and you'll be pretty far behind the curve in a few years when you have to use your replacement equipment. If you couldn't figure out where to get an electric boiler for less than 2x the cost of an electric on demand, then you just didn't do very good research.

Open systems are a horrible idea as well, especially in a vacation home. You just built a massive potential legionella farm. People can get sick from unused shower legs in vacation homes, never mind hundreds or thousands of feet of pex. bad idea. Drinking it isn't the problem: aerosolization from water in showers or the tap is, breathing it is the problem. Please retrofit a heat exchanger at the very least to protect your system, and your health.

Since you're not responding to anyone though, and you just felt the need to post for the first time about "your experience", I have to wonder why. Typically, I would suspect you of being a marketer. Perhaps for "Titan" brand tankless heaters.
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Blueridgecompany.comUser is Offline
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23 Oct 2010 12:51 PM
Rob is right !!
Wikipedia says (cut'n'paste) ; According to the journal "Infection Control and Hospital Epidemiology," Hospital-acquired Legionella pneumonia has a fatality rate of 28%, and the source is the water distribution system.
Open Loop should be called open legionella.
Regards,
Dan
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NRT.RobUser is Offline
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23 Oct 2010 12:52 PM
it's nice to agree once in awhile Dan
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23 Oct 2010 01:18 PM
You Bet Rob,
Onward
Dan <br>BlueRidgeCompany.com
Dave EvelandUser is Offline
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24 Oct 2010 12:13 PM
Since you're not responding to anyone though, and you just felt the need to post for the first time about "your experience", I have to wonder why. Typically, I would suspect you of being a marketer. Perhaps for "Titan" brand tankless heaters.
<!--[if gte mso 9]> Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 Rob, I don’t understand that statement, since I just posted this last night, and you are the first responder! I wasn’t sitting by the computer waiting for a rebuttal. This information was only meant to address a question that has come up frequently on the web – “Can a tankless water heater be used in a radiant heating system”?   Yes, it can, and successfully.

About stagnant water. If the cabin hasn’t been used for a while we just flush the toilet, do a little cleaning, and briefly run the shower and the entire open loop system is replaced with fresh water. Even a thousand feet of ½” pex only hold a relatively small amount of water (I haven’t done the math – it just makes sense).  If you are living in the dwelling there is no need for this – it is constantly being replenished. I think I mentioned this previously.

I am not in any way affiliated with Titan water heaters – in fact, they may not cotton to me mentioning this ‘unauthorized’ use of their product. I just mentioned this brand because it works for us. They use what appears to be regular tank-type elements, and that is necessary with our hard water. I don’t have to periodically ‘acid clean’ off deposits like we do with our ‘closed loop’ solar water heat exchanger. The other 7kw tankless unit we tried used a proprietary nichrome wire-wound element that looked like it wouldn’t last long (but it did).

Now back to your response. Please tell us the reason(s) an open loop system is a “horrible idea”. 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.  

This article was only meant to show the feasibility of the concept for those on a budget who are in a similar situation as we. Not to sell any particular brand. There may very well be a better, less expensive alternative that would do just fine.

I suspect  that you have never tried, much less completely thought out this concept. To belittle new ideas in an effort to look smarter may come back to bite you. Be careful, my friend.

And Dan, thank you for spending the time to read my article. But don’t be so quick to jump on the bandwagon.  Keep an open mind. Dave

Dave EvelandUser is Offline
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24 Oct 2010 12:22 PM
Since you're not responding to anyone though, and you just felt the need to post for the first time about "your experience", I have to wonder why. Typically, I would suspect you of being a marketer. Perhaps for "Titan" brand tankless heaters.

Rob, I don’t understand that statement, since I just posted this last night, and you are the first responder! I wasn’t sitting by the computer waiting for a rebuttal. This information was only meant to address a question that has come up frequently on the web – “Can a tankless water heater be used in a radiant heating system”?   Yes, it can, and successfully.

About stagnant water. If the cabin hasn’t been used for a while we just flush the toilet, do a little cleaning, and briefly run the shower and the entire open loop system is replaced with fresh water. Even a thousand feet of ½” pex only hold a relatively small amount of water (I haven’t done the math – it just makes sense).  If you are living in the dwelling there is no need for this – it is constantly being replenished. I think I mentioned this previously.

I am not in any way affiliated with Titan water heaters – in fact, they may not cotton to me mentioning this ‘unauthorized’ use of their product. I just mentioned this brand because it works for us. They use what appears to be regular tank-type elements, and that is necessary with our hard water. I don’t have to periodically ‘acid clean’ off deposits like we do with our ‘closed loop’ solar water heat exchanger. The other 7kw tankless unit we tried used a proprietary nichrome wire-wound element that looked like it wouldn’t last long (but it did).

Now back to your response. Please tell us the reason(s) an open loop system is a “horrible idea”. 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. 

This article was only meant to show the feasibility of the concept for those on a budget who are in a similar situation as we. Not to sell any particular brand. There may very well be a better, less expensive alternative that would do just fine.
I suspect  that you have never tried, much less completely thought out this concept. To belittle new ideas in an effort to look smarter may come back to bite you. Be careful, my friend.

And Dan, thank you for spending the time to read my article. But don’t be so quick to jump on the bandwagon.  Keep an open mind. Dave
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24 Oct 2010 07:13 PM
Hi Dave,
I installed about 8 open loop systems in the early roaring 90's pre band wagon. I came to the conclusion that they were each a bad idea about that long ago.
Most people do not purge systems, design stagnant loops, have shoulder seasons where water sits for months and month, and do not realize Legonial is contracted by aspirating the bad water. Think shower.
Looking for an approved for heating low cost tank less electric water heater link here http://www.blueridgecompany.com/radiant/hydronic/715/american-heat-electric-tankless-water-heaters . Minimal head full flow, approved as heating appliance by factory.
Chilly rains in the Northwest,
Dan
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Dave EvelandUser is Offline
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24 Oct 2010 10:51 PM
Hi Dan, let me get this straight -  the only problem you (and perhaps Rob) have with an open loop system is the possibility of stagnated water? And you suggest it may be prevented by proper design ("design stagnant loops")?  And yet you still discount this system/concept? I now think maybe the real problem might be that that there is almost no 'profit margin' in a system as I describe (considering if you are 'in the business'). 

The cheapest comparable boiler (11kw) on the site you noted is 4 times the price of (this) tankless. That doesn't include other necessary plumbing items i.e. expansion tank, propylene glycol, etc. (if a closed loop) or 'professional installation' costs. Consider that I could go through 8+ of these tankless units and still save money over a 'professionally designed and installed closed loop system'. Like I said this is not suitable for all cases, but has worked for us quite well. And I suspect it may be of interest to others in our situation as well.

I have surely posted on the wrong site. This info is perhaps more suited to a site such as Youtube or Mother Earth or Countryside magazine. Thank you for your concern and response.  Moderators: feel free to remove this subject thread.     Rob: No need for further bashing. My apologies if I stepped on toes, that was not my intent. Dave
jmagillUser is Offline
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25 Oct 2010 06:45 AM
Dave if you read back through some of the threads you will see that there are others that also use the open system( I being one). Works very well for us.

Most will not responded because of the bashing.
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25 Oct 2010 08:10 AM
One important thing to note.

Stagnant water alone will not result in legionnaire's bacteria.

You need the proper temp water.
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25 Oct 2010 09:32 AM
Dave, Most people who buy and live in houses have very little specialized knowledge of how they work. Closed loop systems are generally safer for the reasons both these guys indicated. Yes someone who takes proper precautions can use an open loop system with minimal risk. Yes someone who does all their own plumbing and has no inspections to deal with can replace things when they fail after 3 or 4 years. There are not too many heating professionals that are going to take the risk of recommending a system that may expose you to a dangerous disease if subjected to operator error or neglect. Nor are they going to suggest doing something that violates manufacturers warrantees. That is called being a professional and minimizing liability.
 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

No disrespect intended, it just does not seem to be worth the cost savings for an open loop system and a nonstandard instalation.

cheers
Eric
Think Energy CT, LLC Comprehensive Home Performance Energy Auditing
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25 Oct 2010 09:52 AM
Dave, I worked for a company that made open loop systems a regular practice for about 20 years (I didn't work there that long, but that's how long their company experience was). I have more experience with them than most people. I have seen some of them succumb to poor water quality. some in Seattle have had grounding/electrolysis issues that result in total system failure, and in other regions I've seen heat source death result in situations I would strongly suspect the same in. That and the health risks are enough for me to say the $500 to $750 for heat exchange equipment is more than worthwhile in all cases. If you can't afford that, then you should be looking at a cheaper form of heat. that's damn cheap insurance right there. Personally, I have paid more than that per month for my family's health insurance, and we're all healthy people... yet people seem to think that's a good idea anyway. Go figure.

Your ideas of what is and is not a risk notwithstanding, when you flush the toilet and run your faucets to "flush" you send air droplets into the air that you can breath and make you sick. the stuff doesn't just "disappear down the drain". again, the whole problem is breathing in the droplets. when you run water in the house, you make droplets in the air. are you going to run your faucets with a gas mask on and open your windows for awhile until you finish purging? For the record, I have no idea if you WILL get sick, but you have greatly increased your risk factors here. that's all.

You can get a heating rated electric unit for not much over $1k if you like. Most domestic rated units are in the $600 to $700 range. There is no MORE need for professional installation in a closed system than an open system, not sure why you brought that up.

You're not stepping on any toes but I'm always deeply suspicious of people who post out of nowhere simply to relay their own "experience". Most of the time, such people have a paid agenda. I'm not still not convinced you are different than that, but it doesn't matter, the merits of your post were lacking anyway. I hope you at least reconsider the heat exchange idea, or separate the system into its own dedicated heater, for the sake of your system and your family. If Mother Earth News doesn't care about your health, so be it. I do. Please fix your system.

as for jmacgill: 70 to 120+ are ideal breeding ranges for the bugs. it's not hard to get there, or close to it, for extended periods of time in a radiant loop field. Fresh water brings in biofilm, radiant tubing gives the ideal home for high-concentration blooms with little dilution. it's just bad practice. it's a bad corner to cut. plain fact. A compulsive maintainer like yourself has worked the angles to make that workable, but when you leave your home, expectedly or not, whoever moves in may be unaware of the risks and maintenance required for your system. I don't think that's very cool either.
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25 Oct 2010 10:05 AM
Dave,
Its not about profit, I can make the same ether way, it is how design and what I like to place my name on. My understanding of a right and wrong choice. Further I provided you an option to but a inexpensive small heat approved electric water heater to use as a designated system. This open VS Closed loop is an old conversation. You will find thousands of open systems working fine. Right, wrong? how about proper. The additional expense is minimal compared to the overall in the cost of your home.
Like I said earlier I have installed several years back, to do over would not do the same. Profit is not the issue.
Dan
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25 Oct 2010 10:24 AM
I pointed out the temperature aspect because it is an important part of the problem.

Many domestic hot water tanks are perfect breeding grounds without the addition of an open radiant system. As an informed homeowner I know that I could move in to any
home and have legionaries present and multiplying in a hot water tank that is set at 110 degrees to 135 degrees. Thats millions of households that have no clue of the danger.


My home has instructions posted by the hot water system on flushing and raising the water temp on a regular basis to kill off the bacteria. It is also in the folder that goes with all the system manuals in case someone else buys the home. Is that cool enough for you?
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25 Oct 2010 10:46 AM
true, but surface area ratio to volume is smaller, and EVERY hot water demand goes through the water heater, and they stratify as well.

I wouldn't consider the risks between that and intermittently circulated, thousands of feet of PEX with lots of surface area relative to a small amount of water as equivalent.

I do recommend a 140 setting for any domestic tank though, as you note. Additional insulation is cheap.
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25 Oct 2010 10:49 AM
It is an interesting situation we have created for ourselves, yes as I understand 110 is the perfect temp, also to note Legionnaires presents its self similar to pneumonia but does not respond to the same drug treatment. Further it will affect the young, elderly and immune system compromised, smokers...
Another aspect of the civilized world post 1920. Flash water heaters will probably minimize these problems going forward but hooking 5,000 feet of warm pipe with out heat exchangers to them will not help.
Off to work,
Dan
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Dana1User is Offline
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25 Oct 2010 10:54 AM
Posted By jmagill on 25 Oct 2010 10:24 AM
I pointed out the temperature aspect because it is an important part of the problem.

Many domestic hot water tanks are perfect breeding grounds without the addition of an open radiant system. As an informed homeowner I know that I could move in to any
home and have legionaries present and multiplying in a hot water tank that is set at 110 degrees to 135 degrees. Thats millions of households that have no clue of the danger.


My home has instructions posted by the hot water system on flushing and raising the water temp on a regular basis to kill off the bacteria. It is also in the folder that goes with all the system manuals in case someone else buys the home. Is that cool enough for you?
135F is hot enough to kill any legionella in the tank, but it'll take awhile.  Flushing the distribution piping with 135F water isn't enough to kill it in the distribution plumbing. (Flush it with 160F water for a few hours and you have a chance.)  Optimal temps for colony growth are between ~85-115F, and fall off rapidly with either higher or lower water temps, but it needs to be at least ~130F for a very long time to kill off an already established colony.  At 140F and up time to colony-death drops dramatically.  You can't kill legionella with lower temps, even if you can halt the colony growth.

When used simply as a hot water heater the setpoint temp of a tankless is irrelevant, since 100% of the water is purged in nearly every draw, and the stagnation temps are room-temp, below an optimal growth temp.  Used in an open-system radiant app the temps are optimally BAD for allowing things to get started and keep on blooming.  Stagnation during the off season isn't the problem- the operating of the radiant system during the heating season is, and no amount of flushing with anything but dangerously-hot water would purge a legionalla colony from the open-loop system.



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25 Oct 2010 11:21 AM
"* 70 to 80 °C (158 to 176 °F): Disinfection range
* At 66 °C (151 °F): Legionellae die within 2 minutes
* At 60 °C (140 °F): Legionellae die within 32 minutes
* At 55 °C (131 °F): Legionellae die within 5 to 6 hours
* Above 50 °C (122 °F): They can survive but do not multiply
* 35 to 46 °C (95 to 115 °F): Ideal growth range
* 20 to 50 °C (68 to 122 °F): Legionellae growth range
* Below 20 °C (68 °F): Legionellae can survive but are dorman
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25 Oct 2010 01:39 PM
So, how is flushing your system occasionally going to fix any problem? Unless you're getting ALL the radiant tubing in an open system up to temp, you're not doing much, which is why protocols for remediation of potable HW distribution call for 160F+ water, much higher than typical for radiant heating, particularly in slabs.

I s'pose you could periodically crank it up until the return water was coming back at 150+ for a coupla minutes or something- would that be on your list of operating instructions? (It could take awhile to get it there in a slab, I would think.)
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