# Tankless Used For Boiler



## Catlin987987 (Nov 12, 2010)

My supplier sells the rinnai 200MBH 94% tankless for $650. It has a flow rate of around 6-9GPM at 140F. What is wrong with using this for a fancoil oversized inorder to work at say 120F and and some infloor in bathrooms for comfort, Install a indirect storage tank for DHW. The water around my area is so hard even with a softner it plugs the heat Extangers of the tankless, so I would be a closed system.


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## OldSchool (Jan 30, 2010)

Catlin987987 said:


> My supplier sells the rinnai 200MBH 94% tankless for $650. It has a flow rate of around 6-9GPM at 140F. What is wrong with using this for a fancoil oversized inorder to work at say 120F and and some infloor in bathrooms for comfort, Install a indirect storage tank for DHW. The water around my area is so hard even with a softner it plugs the heat Extangers of the tankless, so I would be a closed system.


For several reasons this would not be a good choice to use for a boiler.

one being than you intend to use a copper fan coil unit.... if you check the ratings on fan coil you will need 160 to get proper heat out of it....

The other problem is you may be greater than the rated gpm once you install everything you intend to install....

I think you would burn this thing out in no time just from being over worked.

And you could use a much smaller Btu boiler around 80,000 btu and it would do all that....big savings in fuel


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## Catlin987987 (Nov 12, 2010)

I had thought of both of those, 
-You could just oversize the fan coil inorder to deal with the lower water temp
-the tankless heaters are rated XGPM>X temp rise. The temp rise needed would only be 20-30F so I would think the GPM would be a large problem. Most of these units are modulating from 13MBH-200MBH. I have seen controllers which do allow you to raise the temp of the tankless above 140F, but then you loose the condensing factor therefore losing your eff.


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## LEAD INGOT (Jul 15, 2009)

I had a customer that, against my advice, ran his comercial Rinnai at 140 all the time. He blew the heat exchanger out in less than 8 months. Running any equiptment at the edge of it's parameter is never good for the equiptment.


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## Catlin987987 (Nov 12, 2010)

You can get a comercial controller for the rinnai that allow you to run as hot as 185F. I think that most of the tankless heaters can run higher then 140F, they are just limited to 140F for saftey.


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## mselkee (Aug 13, 2009)

Check the head loss across the HX........ur gonna need a big pump just to get 60K btus out of it.


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## Tankless (Jun 12, 2008)

The hard water will destroy the system in no time. You MUST have a sub 12 grains or you will be replacing the entire thing. You stated your temp rist was very minimal...20-30 degrees......? You got solar or something? If you close the radient.....fine but may I suggest going oil and using a small tankless and keep them seperate. Adds more money but your coil over for the heater does need that higher temp. I have messed with many of these and they just suck unless they get their 140f. If it was my design, I would do two units. Heating up then tempering down is about the most retarded thing you can do with a tankless system. It is the opposite of efficient but.....price is king so....


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## Catlin987987 (Nov 12, 2010)

Tankless said:


> The hard water will destroy the system in no time. You MUST have a sub 12 grains or you will be replacing the entire thing. You stated your temp rist was very minimal...20-30 degrees......? You got solar or something? If you close the radient.....fine but may I suggest going oil and using a small tankless and keep them seperate. Adds more money but your coil over for the heater does need that higher temp. I have messed with many of these and they just suck unless they get their 140f. If it was my design, I would do two units. Heating up then tempering down is about the most retarded thing you can do with a tankless system. It is the opposite of efficient but.....price is king so....


 Lets try rewirting that, having alittle trouble getting your message.
Since it would be a closed system, water treatment could fix the hard water problem


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## Catlin987987 (Nov 12, 2010)

mselkee said:


> Check the head loss across the HX........ur gonna need a big pump just to get 60K btus out of it.


 I was looking at a few different brands, and I see that. The rinnai has 50'@8GPM


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