# Tankless Water Heater for baseboard



## Arc_Dad (Dec 23, 2011)

I have a Takagi TK- JR tankless hot water heater in my basement.  It does a fine job heating my domestic hot water.  Can I hook this up to my hot water baseboard?  I would like to have it hooked in to all of my baseboard, but would only use it for about 16 feet of baseboard in my basement.  I have a wood fireplace that heats my 2 main floors.


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## woodsmaster (Dec 24, 2011)

May want to post this in the boiler room. I know this subject has come up in there.


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## eclecticcottage (Dec 27, 2011)

We looked into this as well, but the general thought is that the tankless isn't really built to handle the cycling on/off that a heating system will require and it will wear it out pretty quick.  Funny thing, we can buy a gas water heater, stove or fireplace but not a boiler (by law in NY)-so we thought maybe that would work to keep central heat in the cottage.  We've since removed it and heat only with wood for now, and a small LP fireplace as backup as soon as it's installed.


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## jamierah (Dec 28, 2011)

I'm running a tk-3 using it to heat 1100sq ft in floor radiant and domestic hot water for about 3 years now and haven't had any problem with it. I know the tk-3 is rated by the manufacturer for heating I'm not sure if the jr is.


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## Hunderliggur (Dec 28, 2011)

I use a Rinnai 94 as my backup now, but I did use it for an entire season as the primary heat source for 3500 SF of radiant.  When used as a heating appliance then the warranty was reduced.  Rinnai does not reduce the warranty any longer I believe.  I have had no problems with the Rinnai EXCEPT for 1) a bug in the blower causing an off balance condition, and 2) corrosion on the heat sensor for proof of fire (fixed with a wire brush).  You might want to check the rating on the Jr (BTU rating, GPM at delta T, etc.).  With heating, you are probably only looking at a 20F delta so it should work well for what you are doing.  You may only get about 135 max out of the unit (that is my Rinnai upper limit - I run it at 125).


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## PassionForFire&Water (Dec 28, 2011)

I'm using a tk2 since 2002. The TK3 must be the new model
It's used with an 80 gallon storage tank. This is key to avoid on/off cycling
From the storage tank it goes to 5 heating zones.
All zones are radiant heat.
I use the TK2 at max temp setting of 159F
Not sure if the TKjr is approved for space heating
There is also an indoor wood boiler (hydro-to-heat-convertor model F45) that is hooked up to the storage tank.
So far this winter season we did not use the wood boiler at all.
The house is ICF-construction and my gas bill with these mild temps is around $50 a month for heating


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## Arc_Dad (Dec 28, 2011)

Thanks for the replies.  $50 for heating is excellent.  It sounds like I can give it a try.


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## willworkforwood (Dec 28, 2011)

The previous replies mention radient, which operates at much lower temps than typical baseboard.  You might want to do a heat loss calc on the basement, and then get the manufacturer's specs for the BB you have.  If it's the standard hi-temp stuff, it might not be able to produce enough BTUs from 130* water to heat the space.  If so, you could add more baseboard or replace what's there with a panel rad, but it would probably be better to have that figured out before making any piping changes.


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## Chris Hoskin (Dec 28, 2011)

be sure to use the buffer tank as PassionForWoodandWater describes.  Will limit short cycling and condensation in the heat exchanger (condensation is corrosive and will rot out the thin copper heat exchanger of your TK Jr.).  Also keep in mind that you are now mixing your domestic and heating water so all fittings for the heating system will need to be up to potable standard.


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## DaveBP (Dec 28, 2011)

The rated BTU output of instant water heaters is determined using cold water input temperatures for a very large delta T. So you may not get nearly the rated output when your return water from the baseboards is over 100F. The TK3 is rated heating from 58F to 135F. It will make water up to 167F within its normal setting range. But how many BTUs it can crank out at typical baseboard return temps is not spelled out in the manual.

I know the radiant floor pros usually say that they are less efficient when recirculating heating water.

If you have one heating for higher temps you'll need to put a tempering valve into your domestic line to preventing burns.

And there is always the bogeyman of shared heating/domestic hot water systems... legionaire-type cooties growing in the pipes when the temps are not high enough to sterilize.

Don't know the specifics on the TK Jr.


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## benjamin (Dec 28, 2011)

DaveBP said:
			
		

> And there is always the bogeyman of shared heating/domestic hot water systems... legionaire-type cooties growing in the pipes when the temps are not high enough to sterilize.
> 
> .



It sounds like you have existing baseboard, so in addition to the possibility of lead solder etc. any water heater manual will say to never hook it to anything that was once used for space heat, due to the possibility of boiler treatment chemicals getting into the DHW.  

Be forewarned and give the water to the cat before you drink it.


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