# Tempering Tank - Adding water coil to furnace.



## JRHAWK9 (Mar 17, 2014)

Looks like I may be purchasing a Kuuma Vapor Fire 100 before next heating season.  I'm leaning towards adding the water coil option to it so I can also heat my water during the winter, as we have an LP water heater.  I was advised the best way to do this is by adding an additional tempering tank before the water heater.  Daryl Lamppa sent me a terrific diagram on how to do this.  Looks like I need a 30-50 gallon tank which has a number of outlet positions which I can pick from for hooking up the system.  Daryl mentioned that I visit a local HVAC business and ask them about it, but before I do I prefer to educate myself a bit so somewhat know what I'm talking about and what the cost will be.  So, for those of you who are using a tempering tank in their water system, what brand/model are you using??  If anybody can supply me with some links, that would be great!  I'm having a hard time finding anything online.

thanks!
Paul


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## Vizsla (Mar 17, 2014)

What's a tempering tank? Storage, buffer??


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## JRHAWK9 (Mar 17, 2014)

all of the above...lol  How I understand it it's just a secondary storage tank that is used to feed the water heater.  Some people use them solely to let the air warm up the water closer to ambient temps before being heated by the water heater.  In my case I will be using it for that during the summer but in the winter I will have the water coil from my wood furnace heating the water.


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## maple1 (Mar 17, 2014)

Show us your diagram.


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## JRHAWK9 (Mar 17, 2014)

Hopefully they don't mind I share this.

-HERE- is what a local master plumber recommends for one.


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## M1sterM (Mar 17, 2014)

There are indirect hot water tanks you can buy to handle the tempering.  However, the diagram that you provided can use a standard electric water heater at a tempering tank.  The two inlets from the furnace loop replace the electronic heating elements/ports (or you can use the drain valve instead of the lower element for the lower cold water outlet), and everything else matches up with the standard connections.


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## JRHAWK9 (Mar 27, 2014)

Thanks.  Yeah, that tempering tank I linked to above will not work with how I would want to use it.  It's made for a boiler system which has two separate water systems. 

How fancy of a electric water heat do I need?  Will just a cheap 50-80 gallon one work?  Like below?  It's not going to have the heating element on it, so I would think it would last much longer being used as a simple storage tank.  Comments?

http://www.menards.com/main/plumbin...-6-year-tall-water-heater/p-200179-c-8690.htm


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## brant2000 (Mar 27, 2014)

I'm not sure why a tempering tank would be needed.  The purpose of a conventional tanked water heater is to provide sufficient storage capacity to allow the heating source to catch up with intermittent demands.  Since you already plan to use a hot water tank, that should provide you with more than sufficient storage capacity.  I use a very small sidearm HX that has no problem keeping up with our DHW needs.  To prevent the incoming cold water from mixing and diluting the top of the tank, I simply used a flow switch to disable the HX's circulator while hot water is being drawn.


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## JRHAWK9 (Mar 27, 2014)

I believe you have two separate water systems though.  I only have one water system and that's my potable water supply.  I don't need a separate storage tank, but I feel it's better to have one.

If I weren't to have a separate tank, I could hook things up as shown below.


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## brant2000 (Mar 27, 2014)

So your boiler will have a DHW coil installed in it, correct?  I would recommend simply using a small circulator to draw water off the bottom of your HW tank ->through the DHW HX -> and return into the top of the HW tank.  You can wire it in with the thermostat on the lower electric element, to control the tank temperature.


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## JRHAWK9 (Mar 27, 2014)

No, I don't have a boiler.....I have a wood burning furnace.

With a separate storage tank before the water heater, I'll receive year around benefits as well, as it will then act more as a tempering tank to warm the water up to ambient before being heated by the water heater.


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## brant2000 (Mar 27, 2014)

Then do you plan for it to be insulated or not?  Each would be detrimental in the opposite season.


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## JRHAWK9 (Mar 27, 2014)

If I used a water heater with the elements removed I would just leave it as is with the OEM insulation.  You're right though, insulation during the summer months would go against what I would want to accomplish.


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## JustWood (Mar 27, 2014)

JRHAWK9 said:


> If I used a water heater with the elements removed I would just leave it as is with the OEM insulation.  You're right though, insulation during the summer months would go against what I would want to accomplish.


You could easily add some shutoffs and T's with a radiator close to the tank to bypass the coil and warm up your water in summer months . If you had a south window close by you could put the radiator in the window for some solar gain.


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## M1sterM (Mar 27, 2014)

When using a woodburning appliance to heat a DHW loop, I believe the standard recommendation is to use a tempering or "mixing" tank to ensure superheated water doesn't get directly added into the house water line.  That's why a tempering tank is recommended to buffer the water temperature.


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## M1sterM (Mar 27, 2014)

jrhawk...in your second diagram, where's the cold water supply?  (I still recommend the tempering tank, I think).

Also, have you looked at indirect water heater tanks?  Those use a closed system for the heater running to a heat exchanger in a tank.


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## JRHAWK9 (Mar 27, 2014)

cold water?  who needs cold water?  

Yeah I have.  That's what my first link points to.  You'd need a whole other storage tank for your closed system supplying water to the heat exchanger.  It's not like I have a boiler system where I can feed the boiler water through the heat exchanger.


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## STIHLY DAN (Mar 27, 2014)

JRHAWK9 said:


> Hopefully they don't mind I share this.
> 
> -HERE- is what a local master plumber recommends for one.



This is exactly how I have mine. I do drain and bypass the tempering tank when not in the burning season. In a few weeks I will be adding a 3rd tank post hpwh  for more summer storage to keep it in hp mode.


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