Tankless Coil Should Be Replaced With...?


  #1  
Old 03-15-17, 11:09 AM
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Tankless Coil Should Be Replaced With...?

My parents' Dunkirk EW3 boiler's tankless coil needs replacing, it's having problems keeping up with hot water demand most like due to scaling (it's 14 yrs old). I see my options as this:

1) Replace coil $400

2) Install electric tank ($1000 for SS)

3) Indirect tank ($1000 for SS + circulator, piping, etc.)

I can replace the coil very easily. However every time I read a forum or article people are trashing coils about how inefficient they are. But as far as I know they are the only thing that can deliver unlimited hot water, so there's no worry about dishwashers and washers and sinks and showers running together.

Electric where I am is 12-13 cents / kWH. This is higher than most other places in the country so I'm curious if I'd see a savings from less oil use with the higher electric cost.

Regarding the indirect, I don't see how this is much better than a coil since the boiler still has to heat up the water in the tank.

I am not partial to any one thing here, I just want to most efficient (dollar-wise) long-term solution.

Thoughts?
 
  #2  
Old 03-16-17, 07:25 AM
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The tankless coil is rated for a number of gallons per minute. If water flows through the coil faster than that, then the output water temperature is decreased. So you really wonít get unlimited hot water.

If you look at page 12 of this document for the EW3 boiler you will see that the highest rated tankless coil for that boiler is 4.25 gal/min raising water temp from 40 to 140 - and thatís at boiler water temp of 200.

http://www.dunkirk.com/sites/default/files/396_0.pdf
 
  #3  
Old 03-16-17, 07:43 AM
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Can you add another option by considering treating the existing coil with acid to decompose the scale that has built up ?

Up here, people with hard water have this activity performed frequently enough for it to be a standard offering from oil service companies.
 
  #4  
Old 03-16-17, 07:47 AM
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Zoesdad, regardless of what that manual says, up until a few months ago we did in fact get unlimited hot water. Our well only puts out about 3 gal/min.

Vermont, I really don't want to mess around with the cleaning. If coil is the route to go, I'll just replace it.
 
  #5  
Old 03-16-17, 09:00 AM
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s,
The difference between a tankless coil and an indirect is first, with the tankless, cold water runs through a coil which eventually will lime up, and is heated by the surrounding boiler water which means the boiler must maintain standby temp regardless if you are using hot water or not. This must be done 24/7 365 days a year.

With the indirect water heater the boiler water is inside the coil which heats the surrounding potable water in the tank, eliminating the scaling which means more constant hot water without worrying about liming and flow control going to the coil.

The next thing is the gpm rating on the coil. You do not have to slow the cold water down to the coil, lowering the pressure to the faucets to get hot water in some cases.

Finally, the indirect is an on demand hot water source and the boiler will not have to maintain the high temp all year around but can be used as a cold start application which means the boiler will only run on a call for heat or hot water and not to maintain standby temp saving on your fuel bill.

Depending how much hot water you use and how the coil is set up, although not as efficient may be all you need and will do the job. If you don't mind having your boiler constantly running to maintain standby temp and if money is a concern and you did get 14 yrs. out of the current one the coil may be your best option.

Out of the three options electric would be my last option. You will find it is a slower recovery than the other 2 options which is why you need a larger tank and you are still going to pay the electricity to keep that tank full of hot water even if you don't use it just as you would with the tankless coil only most likely at a higher price.

Just my opinion but if you have the money and the room the Indirect would be my choice. I was in the same situation as you a few years back and I went with the Indirect and never regretted it.

Hope this helps a little.
 
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Old 03-16-17, 09:15 AM
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That stuff makes sense.

The tankless coil is really only a waste in the non-heating months since the boiler is on every so often to deliver heat, right?
 
  #7  
Old 03-16-17, 09:43 AM
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Yes,
During the winter your boiler is going to run anyway and it's like getting free hot water. It's the months we don't need heat that cost you needlessly.

I should add that if this is in an elderly home they may need heat a lot longer than young people so the boiler may be running anyway so it won't make much difference.

Lastly, unlimited hot water to me is a relative term depending how much hot water you require. A family of 5 with the hot water running constantly will be much different than a family of 2 who require much less.

We were a family of 5 with 3 females who I swear made it their mission in life to use every bit of hot water before they got out of the shower and coupled with the laundry and everything else the coil really didn't make much sense but everyone's situation is different.
 
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Old 03-16-17, 02:03 PM
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So you're saying with that demand with the 3 girls a coil wasn't enough?

I've always found the opposite, having 10+ people stay over for holidays and people showering one after the other, running dishwasher, etc. was never an issue.
 
  #9  
Old 03-16-17, 02:37 PM
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Originally Posted by slade8200
". . . I really don't want to mess around with the cleaning. If coil is the route to go, I'll just replace it . . ."
That of course is your choice . . . .or that of your Parents; but just to clarify my suggestion, I checked with a Friend who performs this service here in Vermont, and he charges between $75 and $150 depending upon how easy it is to isolate the piping to and from the tankless coil.

He treats the inside of the coil with a solution of 20% to 30% Muriatic Acid, diluted with distilled water, and he'll circulate the acid with a small pump for 15 minutes to an hour . . . . vacant houses may be treated overnight; and thoroughly flushes the acid (which is a POISON) out of the system. He says that there's no clean-up left for the HomeOwner to perform. Maybe other people leave a mess ?

I mention this only because other visitors to this thread might be interested, especially since this is still a Do It Yourself Forum . . . . while other people go over to that FindSomeoneElsetoDoIt.com Forum.
 
  #10  
Old 03-16-17, 03:24 PM
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No, not exactly. We did end up having enough after I did some work to it with an acid treatment as Vermont mentioned and repiping it the proper way. I actually inherited the problem when I bought the house.

One thing to note is I had a much older boiler at the time which was very large in comparison to todays boilers so the coil back then worked a lot better because it sat in a large volume of hot water so the coil really picked up the heat transfer. My old boiler had about 50 gallons of water where a typical 3 section today has about 12 so when the heat comes on it takes no time to empty that boiler and replace with cooler system water affecting the coil output until it catches up again.

After I got it set up we never did run out of hot water no matter how hard they tried. The reason I changed mine was because I replaced the boiler and just chose to try the indirect which was a fairly new concept at the time.

As I said each case is different. The only thing I would caution you about with the acid is it does raise a little havoc with the copper. Each time it is cleaned the acid removes a little copper and if the coil has any weak spots it could puncture the coil and you end up with acid in your boiler water, and then the coil must be replaced anyway so I used to always make the customers aware before I did it.

I never had one let go but I know of others that did and for that reason a lot of companies don't want to do it anymore and don't offer it. The big thing is the acid must keep moving. If you get a coil that is plugged so bad even the acid can't get right through that's when it will eat the copper in the coil and you end up with a hole and must replace the coil anyway.
 
  #11  
Old 03-17-17, 07:11 AM
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I'm guessing that the coil has probably been underperforming for quite some time, but it didn't become a real inconvenience until just recently. Is it just your parents that live in the house?

Once upon a time I had a coil setup for DHW and it worked marginally - at best. When my sister gave me a used Amtrol Boilermate I figured "what the heck" and plumbed it into the existing boiler piping. The difference was night and day. I had almost forgotten how nice it was to have a shower in my own house that didn't run out of hot water after 5 minutes!

So based on my own experience, my first instinct is to recommend dumping the coil and going with a tank of some sort (other than electric).

However, if funds are tight, $100 or so for a professional cleaning of the coil doesn't sound like a bad deal. Anything more than $200, then IMO you'd be better off just replacing it.
 
  #12  
Old 03-17-17, 08:07 AM
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I used a pump to flush coils but a stand pipe is a ligit. way to clear them.
 
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Old 03-17-17, 08:10 AM
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Honestly I never considered the cleaning to be an option because I figured the price would be equal to that of a new coil anyways. But if you say some charge $150 that would be worth it. I'll see what's around.
 
  #14  
Old 03-17-17, 01:12 PM
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OK let me throw some crap in the punchbowl (LOL) Ė to be taken with a large grain of salt. Iím no expert for sure.

It may not be that easy to replace the coil, depending on your skill level. You will have to do some plumbing and probably will have to cut and sweat copper pipes. You have to drain some water out of the boiler and afterwards put water back in. So you have to hope that the shut off valves and fill valve works properly, if not then there will be another job(s). (Sometimes a fill valve sits in the totally closed position Ė like mine. There are debates about whether the fill valve should always be OPEN or CLOSED).

Sometimes the bolts holding in the coil break when you fool with them.

If you get a plumber to replace the coil Iíve heard prices anywhere from $700 to $1,000. I personally would first try the cleaning.

I think on your other thread you said the low limit was set at 140 (although you said the boiler water temperature was a constant 175). If you set the low limit up higher (assuming the 175 was a mistake) you will get hotter water. Maybe thatís all it needs.

(I had to set my low limit to about 150 before my shower was hot enough Ė and thatís with a low flow showerhead Ė I think maybe 1.75 gals/min)

Just my opinion.
 
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Old 03-23-17, 08:43 PM
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Called 3 places with highest yelp reviews around me for a price for coil cleaning. $350, $600, and $1200.

I think I'll be replacing it myself haha.
 
  #16  
Old 03-24-17, 03:45 AM
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Where in Mass are you ?

My Friend says he'd consider coming down to do it while he ran a few other errands in the Bay State !
 
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Old 03-24-17, 05:57 PM
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Very kind, thank you... but we have decided to go with the replacement route!

On a side note, one of the guys said to choke down the cold water going into the coil and this should help because it will heat up more. Sounds like BS because this would just give you less hot water at the shower.
 
  #18  
Old 03-24-17, 06:34 PM
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If city water is high no big deal to open a hot upstairs choke it down at boiler and grab the outgoing hot pipe at coil and see how long it will last. Might have to do some different setting slowing it down. Here the psi is 160. I do my whole house at 60. But I have warm air.
 
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Old 03-25-17, 08:03 AM
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"Sounds like BS because this would just give you less hot water at the shower".

It is far from BS. All tankless coils have a GPM rating and any water coming into the coil over that rating is just wasted water and the coil is not going to be as efficient in producing hot water.

There are flow restrictor valves especially made for tankless coil installations to match the coil output although very few people use them and honestly don't know if they know about them. By running more fresh water through the coil than it can handle is just a waste of water and shortens the life of the coil because every time fresh water is introduced into the coil it leaves mineral deposits which eventually kills the coil. as it did to yours.

In your situation where you only get 3GPM anyway none of this applies but the normal residence that has city water delivers about 7GPM and if a tankless coil is used, the right way to set it up is by installing the proper restrictor for the coil output. As was mentioned and repeated by you it does lower the pressure in the faucets but that is the trade off and drawback of the tankless coil.

Again this has nothing to do with you at 3GPM as your water would be only dripping out if you cut back the flow at all, but the suggestion to be clear was NOT BS.

Hope this education was a little helpful and good luck with your new coil.
 
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Old 03-25-17, 07:10 PM
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Yes I get that. I meant the BS for my situation.
 
  #21  
Old 03-25-17, 08:04 PM
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With an existing tankless coil based DHW system there are several ways to increase capacity.

One is to add a storage tank ( 30 to 50 gal) and temperature activated circulator pump to maintain set temp. Since most boilers are very oversized it is a very effective solution.

Unfortunately using the main boiler in the summer for DHW is very inefficient.

Instead of a storage tank, install a separate oil or gas fired hot water heater. In the winter use a circulator to heat it with water from tankless coil. In the summer shut down the boiler and directly fire water heater.

This makes for a very efficient setup with plenty of hot water and avoids the issues of firing two systems simultaneously on a common chimney.

Have a 60 year old Weil McLain boiler with tankless coil feeding water heater for 20 years. Only issue was plastic impeller on Taco 007 circulator was eaten up by rust particles in water. Installed a "whole house" filter on cold water feed to end that.
 

Last edited by doughess; 03-25-17 at 08:50 PM.
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Old 05-17-17, 11:09 PM
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Ok, so I haven't done the coil yet, but I did find something interesting. Someone at a plumbing store told me that if you shut off the cold going to the mixer, the mixer will sometimes limit the mixed output. Since I have that valve to kill the cold to the mixer, I figured it was worth a shot. I opened the cold to the mixer and cranked the temp setting all the way to 175 on the mixer. Since I did this the hot water has been consistently hot. I'm still going to do the coil but wanted to share this story, because I've never heard of a mixer acting that way before.
 
  #23  
Old 05-18-17, 07:29 AM
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I donít think you mentioned the mixing valve before (could be there, I just donít see it). That sounds like it was probably cranking the temperature up to 175 that made the difference. You changed two variables at the same time: opening the cold supply and changing the mixer setting.

I didnít think you could set a mixer up to 175 Ė but Iíve never used one. Or are you talking about setting the low limit on the Aquastat up to 175?
 
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Old 05-18-17, 07:34 AM
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No no the mixer was always at 175, I was just reiterating it.

I'm talking about the mixing valve with the green cap... Haven't touched anything on the aquastat.
 
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Old 05-18-17, 07:52 AM
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I opened the cold to the mixer and cranked the temp setting all the way to 175 on the mixer
OK - so what you really mean is that you opened up the cold supply to the mixer, which prior to this point in time was closed. But you DIDN'T crank up the temp setting.

How do you know then that the problem is (or was) the coil? Why can't it have been the mixer all along?
 
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Old 05-18-17, 07:58 AM
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Maybe it was chocked full of mineral deposits, and you dislodged some of them when altering the setting, and increasing the flow of hot water ?
 
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Old 05-18-17, 08:10 AM
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I mean it could have been the mixer all along, but I thought it was the coil because the pipe temp would drop a good amount after using the water for a short time.
 
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Old 05-18-17, 08:57 AM
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Well I guess when you think about, if the cold was turned off to the mixer, then I guess it would be pretty hard to see how the mixer could cause the hot water to become colder. That would seem to eliminate the mixer.

But then why when you now supply cold water to the mixer, the hot water output seems better? Something strange at work here Ė lol!
 
 

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