# snow melt with a tankless water heater



## Dude from NJ (Jan 22, 2009)

I'm using a Rinnai for a snow melt. First time. Can't seem to trick it to stay on. I've got about 900 ft. of 1/2" tubing. I'm using a Grundfos 1/25 and I'm going to try the 1/6 (high head) next. Should it be on the supply or the return side? I get different answers from the reps. What about an expansion tank (also different answers).


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## Bill (Jun 17, 2008)

There you go Dude, now it wont get lost.
Just hang in there, we do have some people who deal with this. I am not one of them though!


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## WestCoastPlumber (Jun 17, 2008)

If you go through the rinnai book they show how to do return lines, I would tie it back into the cold past the check valve, This way second go around the water does not have to heat up as much. if you are using a Rinnai, use a Metland pump, they have a pump designed just for flow rates on Rinnai.

Expansion tank is required because you have a check valve and it is considered a close system

I am very sure Tankless will ahve a deeper answer for you. He is our tankless god


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## Tankless (Jun 12, 2008)

Mods....can this get moved. I'll be happy to offer my 02

edit: I meant get moved to whatever section you want....just not in the intro section!!


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## Dude from NJ (Jan 22, 2009)

I've talked to Rinnai. They are the ones who suggested the Grundfos. I'm pretty sure it's plumbed OK. It would seem to me to be some kind of a pressure problem. I can get it to run for about 15 min, then it flames out. It's not the unit, as a test, I by passed all lines and ran fluid right in and out of the unit and it fired continuously.


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## Bill (Jun 17, 2008)

Tankless said:


> Mods....can this get moved. I'll be happy to offer my 02
> 
> edit: I meant get moved to whatever section you want....just not in the intro section!!


Done


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## Dude from NJ (Jan 22, 2009)

Where should I be looking?


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## Tankless (Jun 12, 2008)

Reps are idiots...most of them anyways...
Recirc pump is typically on the return line, but because you have a closed system, mechanically, there is no difference. If I was doing it would be on the return with an Xpan tank...set the tank's PSI to line pressure. Hmmmm, well is it a closed system? Are you using the tankless for ONLY the snow melt? If so, are you using oil or water?

What mdl of tankless are you using...Nat gas or LP, does the unit have a remote or are you controlling it with the dip switches inside?

Got any pictures of how it looks?

Is the pump noisy? How hot is the pump getting?
Is the pump just not shutting off and the tankless is after 15 min?
Do you have an Aqua stat on the return line? If so what mdl of stat is it?
I'll ASSume you're in Jersey...and is this snow melt line doing any kind of radient heating or just the drive way / walk way?
What temp do you have the heater set to heat to? Do you know the temp of the supply water (assuming it's water and a closed system for snow melt only).

The answer to your issue is in the details but I already know why it's stopping...answer the questions so I can give you the best solution possible.

It's raining here and the crawl space I needed to get in and out of today got kinda flooded...and my barber is booked up so I am at home watching Obama making an idiot of himself again on TV!!!


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## Dude from NJ (Jan 22, 2009)

Now we're talkin. See my resp in red



Tankless said:


> Reps are idiots...most of them anyways...
> Recirc pump is typically on the return line they told me it should be on supply side. I'm thinking it should be on return in order to give the unit the most flow/pressure, but because you have a closed system, mechanically, there is no difference. If I was doing it would be on the return with an Xpan tank...set the tank's PSI to line pressure. Hmmmm, well is it a closed system? Are you using the tankless for ONLY the snow melt? Snow melt only If so, are you using oil or water? glycol
> 
> What mdl of tankless are you using Rinnai REU-V2532FFUC-C85...Nat gas or LP Nat, does the unit have a remote or are you controlling it with the dip switches inside? I'm using a Danfoss temp controller with slab sensor tied to a Argo controller which activates circ pump
> ...


 Thanks


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## Tankless (Jun 12, 2008)

Ok,....I think I got it figured out. The slab sensor...is it an F7H?
No matter, it's just a capillary. I prefer the old Honeywell setups but your is good aswell. The Danfoss temp controller.....happen to know the mdl# on that? Is there any kind of storage/handler tank for your oil? I doubt there would be, just asking.

The Argo controller....how many stages is it? Assuming it's just one, that would mean just one pump, correct?

I know the cause of your issue, but the reason is another story. You need to make sure that slab sensor is still alive. Something is not telling the Argo to turn off your Grundfos pump. Need to get the nyumbers from tech support for the resistance in that capillary. usually the hotter the more resistance. Does the Danfoss temp control;ler have a digital readout? If so, what temp?

Reason your heater is shutting down:

Pay attention everyone this is important;

When we ask a heater for 120 degrees of output that's what it wants to do. If we ask 140....or whatever temp, that's all that heater wants to do in life...to serve you. The heater and its computer assume you have installed it correctly, I'll assume the same in this situation till I see/hear otherwise.

If we ask for 140 from the tankless, and your slab capillary tells the temp controller when to turn on, and the Argo takes that mili-volt signal and relays it to line voltage and that kicks the pump on, the pump will do what it is made to do...pump. The pump you have is strong, it's cast iron body is just fine for a closed oil system. Anywho, you've asked for 140 and the pump gets it signal at whatever "temp to activate" is....could be 30f could be 10f...I don't know. Assuming it's...say 25 degrees F, you will be delivering to the heater....so input is 25 output is 140.....that is bad...









Bad in a sense of heater operation...that's less than 2 gpm on that heater...and I seriously doubt it could even do that. The graph for your unit doesn't go that low. However that (at the moment) is neither here or there. So your heater is chugging along at 140 output and it's running at 100% burner, fine. Eventually that oil will make its way back to the input of the tankless, that will slowly start to increase in temp...25---35--55-85-105--125 than STOOOOOP....the heater shuts down, all you hear is the pump running....but why you ask yourself? Well it's very simple. remember your tankless only wants to serve its master (that's you:laughing BUT --BUT-- when you're delivering 125 on the input and and only asking for 140 the heater says to itself "hay...wait a minute I'm getting 125 and you're wanting 140 well shoot, that's only 15 degrees of rise...my boss don't need that extra 15 degrees". And the heater decides for him (or her) self to shut it down. 

It's basically telling you, I'm a tankless heater not some silly warming plate. It wants to work hard for you, 15 degrees is not working hard.



FWIW I typically see this shutdown at 105 to 110 on a target temp of 120-125.

So what happends than?
Well here's the expensive part Dude....
Your heater is now a monitoring system....Its flow control valve is spinning, the servo motors are making micro-adjustments the gas solonoids are adjusting for the right amount of fuel in the burner chamber but there is just one thing holding it back, the thermisters on the input and output of the tankless. They are too close together and the tankless engineers told the computer to wait till there is about a 20 degree difference before firing up. So your cycling all that oil and it's not doing anything for you, other than killing your tankless and the added wear and tear on your plumbing as well as paying for the electricity to run your pump.

Tankless heaters make crappy temp monitors and I see this all too often. Last one, I wound up replacing the flow sensor...both input and output thermisters...2 gas control valves and finally the main motherboard...Why? because the heater wore itself out...it was 5 years old. That lady just finished paying my bill last night...she wasn't happy, but she understood what had happened.

Lady and Gentlemen that read this, if you decide to do tankless with recirculation you CANNOT treat it like a tanked installation....it just doesn't work.

So, Dude from the garbage state...errr sorry, the Garden state please post up your exact specs on your controler / slab thermister / and your Argo unit. Pics are always nice....I loke looking at others work. But your issue is electronic and if you understood all that I just said, you also know it has nothing to do with your tankless heater.
I really should start charging for all this...Nathan....ya hear that?:laughing:




Links I found attempting to see what you have, but I could be off:

Argo: http://www.argoindustries.com/products_hydroair_controls.asp
Rinnai: http://www.foreverhotwater.com/model-c85i.php

Danfoss: http://www.radiantcontrol.co.uk/downloads/Danfoss thermostat info leaflet.pdf (see bottom)


Grundfor pump: http://www.plumbersurplus.com/Prod/...HP-Recirculator-Pump-(59896341)/10985/Cat/539


remember, the answer is in the details:laughing:

edit to add:

One other thing I forgot.....after your unit fires up...heats all the oil than shuts itself down while the pump is still running, I bet after ...I dunno maybe 30 minutes...1 hr....the heater fires back up and does this cycle all over again.....is that about right? I would expect it to be I just don't know the viscosity of your oil and its heat retention characteristics....but I bet after about 20 degrees of temp fall AT THE HEATER INPUT the heater will fire again.


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## Tankless (Jun 12, 2008)

Dude from NJ said:


> I've talked to Rinnai. They are the ones who suggested the Grundfos. I'm pretty sure it's plumbed OK. It would seem to me to be some kind of a pressure problem. I can get it to run for about 15 min, then it flames out. It's not the unit, as a test, I by passed all lines and ran fluid right in and out of the unit and it fired continuously.


I missed this post by you.....so, ya wanna take a guess how long it takes your Grundfos to pump oil through 900 feet of pipe and back to the heater? I'm guessing about 15 minutes!!

Maybe someone on here who is smarter than me can calculate that pumps ability to pump oil through all that head and back...I'd like to hear those numbers


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## rex (Jun 13, 2008)

lets say it takes 15 min to pump the water through the tubes if its for snow melt its going to return way less than 20 degree differential.......thats why tankless are perfect for snowmelt as long as you have the flow rates..... i designed my last job by my self it took lots of tweaking but i fianally got it....

if you were to use the tankless for space heating youd need a storage tank so that you arent returing such high temps or do a close spaced t system with ball valve and throttle the valve just enough so it returns cold of enough water to satify the unit..

im not a fan of the bull **** electronic systems would rather go standing pilot cast iron but i tried some thing different and it worked


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## Tankless (Jun 12, 2008)

> What temp do you have the heater set to heat to? 140 Do you know the temp of the supply water (assuming it's water and a closed system for snow melt only). Don't have a stat on *supply* but it is *very hot* to the touch


Every system will be different, however there is not that much thermal loss. Once the crete warms up around the pipe, it now acts like an insulator of types therefore allowing less and less thermal losses...to the point where (see quotes above)


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## rex (Jun 13, 2008)

you are basiclly heating the out doors that theory works in a insulated building but for snow melt thats not true you are battling below freezing temps and trying to get a huge slab over 32 degrees.....with absolutley no over head insulation......yes the system i installed gives 160 degrees and returns 80 degrees with high head/flow pumps....so the thermal insulation therory is some what true.....but heating a indoor slad vrs outdoor is different


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## Dude from NJ (Jan 22, 2009)

*snow melt probs*

So, lets rock and roll...



Tankless said:


> Ok,....I think I got it figured out. The slab sensor...is it an F7H?
> No matter, it's just a capillary. I prefer the old Honeywell setups but your is good aswell. The Danfoss temp controller.....happen to know the mdl# on that? Is there any kind of storage/handler tank for your oil? I doubt there would be, just asking.
> 
> The Argo controller....how many stages is it? Assuming it's just one, that would mean just one pump, correct? Right
> ...


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## Dude from NJ (Jan 22, 2009)

rex said:


> you are basiclly heating the out doors that theory works in a insulated building but for snow melt thats not true you are battling below freezing temps and trying to get a huge slab over 32 degrees.....with absolutley no over head insulation......yes the system i installed gives 160 degrees and returns 80 degrees with high head/flow pumps....so the thermal insulation therory is some what true.....but heating a indoor slad vrs outdoor is different


 
I've done some research. 100-125 btu/sq over comes thaw freeze cycle in my area. I'm sized OK


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## Tankless (Jun 12, 2008)

All right, let me give this a go and let's have some fun....

First, if I understand you, your assuming my return temp is close to my set temp. Even with no guages on the lines, I can tell you it's not even close. Really? Because I asked you and you stated it was "very hot".

The unit should sense cold water and want to keep firing.

The heat controller is out of the equation, because I jumped out the contacts to activate. No problem.

So far, I have been following the reps advice. I am familiar with radiant systems. I've done at least 100. BUT never with a tankless. And never for a snow melt. I liked the 0 footprint being that it's in my garage.

Any way, Mr. Tankless, after pondering for a bit, this is what I think my problem is. Tell me what you think.

The tankless is just a dumb machine that is supposed to turn on when someone opens a faucet. It recognizes a drop in pressure, and assuming the homeowner has at least 30 psi thru the unit, it will kick on. ummm, not really... Tankless are rather smart...but I see your point. Tankless units are detecting flow, not pressure drop. Your unit claims .5 gpm to remain active...but it's more like .8 to .9 to keep running.

http://www.foreverhotwater.com/faq.php#q20


A closed loop is a bit different. Unless the Rinnai senses that pressure drop it will not fire. The 1/25 Grundfos I have on there has enough kick to get things going. But after while the head overcomes the pump, and while the pump keeps pumping, it's not at full cap. Not to mention It's on the supply side as they recomm. 

Since then, I've done some head calcs. I'm lookin at abot 30'. I'm going to put in a 1/6 high head in place of the 1/25 (as I previously thought) on the supply side. If that doesn't work, I'll probably say alot of nasty stuff then put the 1/25 on the return side, where I really feel it needs to be to tell that dumb thing to stay on along with the high head pump on the discharge side.

What do ya think? 

Even with 30 feet......hmmm.....Here's what you do:
Install that pump on the return side...it really should be on that side anyways. Try that first.....but I also have a feeling that pump is undersized. I guess I missread into your answers....when you said the incomming was really hot than that means what I already wrote up for you. now you say that it is cold. That means your pump is undersized and or installed on the wrong piping. However that shouldn't make a huge difference. I looked up the specs on that pump...you must have alot more head to drop below a 1/2 gpm......


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## Dude from NJ (Jan 22, 2009)

I had a gut feeling the original pump they suggested was undersized. I'm used to indoor radiant systems using domestic h.w. boilers. You can get away with much smaller pumps on that set up based on how those boilers run. This is my first experience with a tankless.

The new pump I'm going to put in is a 1/6 Grundfos high head. Specs say it should handle my 30' at about 5 gpm. This should do it. It's my project for Sat. I'll let you know.

By the way, I have the tubing tied to a 5 loop manifold so it doesn't take any more than about 3-5 min to circ the water. I can tell by the bubbles when I purge the system. Thanks.


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## Dude from NJ (Jan 22, 2009)

I'm also going to ignore your comments about my lovely (overtaxed) state.


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## ASUPERTECH (Jun 22, 2008)

Dude from NJ said:


> I had a gut feeling the original pump they suggested was undersized. I'm used to indoor radiant systems using domestic h.w. boilers. You can get away with much smaller pumps on that set up based on how those boilers run. This is my first experience with a tankless.
> 
> The new pump I'm going to put in is a 1/6 Grundfos high head. Specs say it should handle my 30' at about 5 gpm. This should do it. It's my project for Sat. I'll let you know.
> 
> By the way, I have the tubing tied to a 5 loop manifold so it doesn't take any more than about 3-5 min to circ the water. I can tell by the bubbles when I purge the system. Thanks.


Have you tried turning the temp down on the heater?
Say to 100-120, this should also allow greater flow rate, as well as keeping the drive clear I would think. It's also cheaper than a new pump...


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## Dude from NJ (Jan 22, 2009)

The only problem with that, is my output will then be below the necessary level to melt all the way through the snow fall and will create the 'igloo' effect. This approach may work on a 1-2" snow fall, but I really want to hit the 5-6" range. Thanks for the comment.


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