# Tankless Water Heater Running Baseboard and DHW Clogging



## Marlin (Aug 14, 2008)

Tankless units are a rarity around here and I don't have a lot of experience with them. I have a customer who has a tankless unit running the DHW and a cast iron baseboard zone. I forget what the unit is running at but it's as high as it will go, probably 150ish. They have a mixing valve to knock the domestic down to 120 and a heat exchanger for the baseboard zone. On a side note the arcitect who speced the system didn't see fit to put an expansion tank on the heat side and the plumber who installed it didn't catch it. Instead they piped the relief valve to a sink and the homeowners don't want to hear about putting one in. :wallbash:

Anyway, the system apparently worked fine the first five years. Last year water wasn't flowing through the unit and I went there and flushed it out with viniger and water for about half an hour and that solved the issue. Ten months later they're back in the same boat. 

Are you supposed to be able to run heat off these things or are they not really made for it? I can't see anything inheritantly wrong with what they're doing but it must be causing a lot of excessive wear and tear on the unit, am I wrong?

Secondly, is their some trick to flushing these that I missed and didn't do the job correctly? Is half an hour enough or is this somewhere where I should but the pump on, leave and come back at the end of the day?

Oh and they're on the ocean to, you should see what the salt is doing to the aluminum in the thing. This seven year old heater looks 20 with the salt and all the use it gets.


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## Ncplumber84 (Dec 30, 2014)

Marlin said:


> Tankless units are a rarity around here and I don't have a lot of experience with them. I have a customer who has a tankless unit running the DHW and a cast iron baseboard zone. I forget what the unit is running at but it's as high as it will go, probably 150ish. They have a mixing valve to knock the domestic down to 120 and a heat exchanger for the baseboard zone. On a side note the arcitect who speced the system didn't see fit to put an expansion tank on the heat side and the plumber who installed it didn't catch it. Instead they piped the relief valve to a sink and the homeowners don't want to hear about putting one in. :wallbash:
> 
> Anyway, the system apparently worked fine the first five years. Last year water wasn't flowing through the unit and I went there and flushed it out with viniger and water for about half an hour and that solved the issue. Ten months later they're back in the same boat.
> 
> ...


I have never seen anyone use a thankless for home heat so not sure bout that one we always install tank type for that kinda situation. Given the age of the heater if it has never been descaled I would do it at least an hour. Most people install service vales you can turn the water off and flush with. Also nortiz have a wire you have to connect when flushing or it will lock down the heater eventually and won't fire until its flushed.


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## paultheplumber1 (May 1, 2014)

Using a high efficiency water heater to heat a zone of cast iron baseboard? Doesn't sound like a good idea to me. I'm willing to bet that unit is working way to hard. On top of that the water in that baseboard system is gonna be pretty dirty. Sounds like a poorly designed set up too me.


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## jmc12185 (Aug 27, 2013)

paultheplumber1 said:


> Using a high efficiency water heater to heat a zone of cast iron baseboard? Doesn't sound like a good idea to me. I'm willing to bet that unit is working way to hard. On top of that the water in that baseboard system is gonna be pretty dirty. Sounds like a poorly designed set up too me.


 I'm guessing you missed the part that said there's a heat exchanger on the baseboard zone. The water that's in the baseboard never goes through the heater.


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## paultheplumber1 (May 1, 2014)

Yup did miss it. Was more concerned with the max temp of the water only being 150 to satisfy cast board.


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## Marlin (Aug 14, 2008)

They have enough radiation that 150 degree supply water is enough to heat the place so that's not an issue. 

Not having much experience with these tankless units I just wanted to confirm my suspicion that the unit really isn't designed for what they're doing and they can expect increased wear and maintenance as a result. I'm going back this week to flush it out again and I'll try letting it go for an hour to two to make sure it's clear. 

I'll talk to them about going to something like a Triangle Tube Challenger that will be better suited to the application. I think they're determined to ride this thing out to the end. Won't be too far away with no expansion tank on the heat side. No service valves for flushing either and no room to install them without re-piping everything. It's all pro pressed and their is not enough pipe anywhere to put a fitting. I have to pull the relief valve and pull the plug on the wye strainer to get points to flush from.


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## timrath (Sep 28, 2013)

What is the most model and make of the unit? I would imagine the unit would never work well on the heat side due to the temperature difference and lack of a dhw priority setting that combo boilers have. Usually on a really cold day you need 180 degree water to offset heat loss. Are you in a warmer or colder climate?


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## jmc12185 (Aug 27, 2013)

I have never seen it done but depending on the heater they have, I don't really see anything wrong with the set up you explained.


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## Catlin987987 (Nov 12, 2010)

I have seen it done a few times, They work too hard and die early. I bet the pump they are using is grossly oversized, and it will die from a pin holed heat exchanger.


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## joecypress (Jun 16, 2009)

De-scaling every five years is not enough. They need to be de scaled a minimum of once a year. I have three of them in series at a commercial laundry i have to de scale every six months. They are very sensitive to this. It makes them overheat and then shut down.


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## SewerRatz (Apr 25, 2009)

Descaling with vinegar is at least an hour per unit, changing the vinegar as it looses it strength. I use flow-aid one quart to four quarts of water, it shortens the descale time down to thirty minutes. But with a heater that has not been descaled in 5 years, I would let it run at least an hour with the flow-aid. 

The tankless unit needs to be delimed once a year, there are no ifs ands or buts about it.


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## HonestPlumb (Jan 25, 2015)

Anyone have any thoughts on a tankless unit for radiant for my driveway ? Getting sick of snow blowing and shoveling. Getting ready to have the driveway done over, so figured it would be a nice idea and a good selling feature. Diveway measures about 500 square feet. Don't have a boiler for my house , only hot air. Obvious alternative is to through in a little Weil-McLain CG. Just looking for a less expensive and easier way. Thanks to anyone ahead of time !


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## Catlin987987 (Nov 12, 2010)

HonestPlumb said:


> Anyone have any thoughts on a tankless unit for radiant for my driveway ? Getting sick of snow blowing and shoveling. Getting ready to have the driveway done over, so figured it would be a nice idea and a good selling feature. Diveway measures about 500 square feet. Don't have a boiler for my house , only hot air. Obvious alternative is to through in a little Weil-McLain CG. Just looking for a less expensive and easier way. Thanks to anyone ahead of time !


A combi unit might be a good fit


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## paultheplumber1 (May 1, 2014)

I have a customer of mine who did his driveway in radiant. He uses solar panels and an 50 gal gas fired tank, all set up in his garage. It does the slab of his 4 stall 40x40 garage and and his laneway which is at least 300 yds long. He also had a couple electric panels installed to power the circulators. He's says he uses less than a full tank of gas (200) per season.


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## Texan (Feb 21, 2015)

Probably too late for the op to use on his job. But for future reference Noritz and Rinnai recommend , and do not warranty the units heat exchanger unless, the unit is descaled once a year. Electric must be left on and the gas turned off. This is so the bypass servo will let the descaler into the units heat exchanger. Often times the gas manifold pressure will be off after a few years. That should be checked with a manometer at the test port. Call manufacturer for settings.


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