Author Topic: Any experience with indirect water heating for potable and radiant heat?  (Read 207 times)

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Offline NM_Shooter

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I need to replace a boiler for my radiant heat, and a water heater.  I'm thinking of using one boiler with a storage tank.  The isolated kind, where the boiler is attached to a heat exchange coil in the tank, so my radiant heat water and my potable water don't co-mingle. 

I'm trying to understand the basics of how something like that works, and I have not found much in the way of schematics on the web. 

The closest thing I can find is this :https://www.google.com/search?q=indirect+water+heater+schematic&rlz=1C1CHBD_enUS711US712&source=lnms&tbm=isch&sa=X&ved=0ahUKEwja_tWRxufWAhXpzVQKHehmDXIQ_AUICygC&biw=1366&bih=662#imgrc=plBtOPyKffFLEM:

I have some concerns....

1)  My existing system circulates water out of the boiler which is ~120 to 140 deg F upon exit from the boiler.  Sort of depends on how many zones are on.  I have read that indirect systems circulate much hotter water.

2)  I know that I can use a Taco mixing valve to down-regulate the heat that goes into the floor.  But.... I don't like the idea of having a 50 gallon tank full of water which is greater than 120degrees F. 

3)  Seems like I would want to have a system that uses a hydrostat and valves to keep the tank water at no hotter than 120degrees, and allows me to bypass the hot water storage tank when I want to heat my floor and the water tank is already at temperature. 

Some questions...

Q1)  For an indirect water heater, do most of these systems store large quantities of water which is much hotter than standard hot water tanks (120degF?).

Q2)  For indirect water heaters, I think I read that the source temperature out of the boiler is on the order of 190deg or so.  Is this correct?  (Dang!)

Q3)  I'm looking at a down-converting 10:1 boiler.  How does the boiler "know" when to down-regulate?  Does it sense the boiler loop temperature automagically and operate off of that?  Can I set the temperature of the boiler, or is this simply set at some ridiculously high temperature?

Q4)  Anybody have any reference material that I can review? Trying to put together a system without finding a decent schematic is puzzling. 

Again, the goal is to be able to heat water to a reasonable temperature, without overheating that tank full of water.  If the boiler is putting out 190deg or 200 or whatever, I have to have a way to put the boiler water to the water tank into bypass when my house needs heat.

Are there controls which manage the bypass valves? 

Ugh.  I need to be smarter. 

Thanks!






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Offline JRR

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Re: Any experience with indirect water heating for potable and radiant heat?
« Reply #1 on: October 11, 2017, 06:48:29 AM »
I personally would not consider a single boiler for the two functions, as it is almost impossible to guarantee that the two streams cannot cross-over in some leak event, or other failure.

I believe two separate systems could have far less total overall complexity, (fewer control valves and sensors, different temperature operating ranges) and would be inherently safer for the potable water supply.  You will want the house heating system to be filled with anti-freeze, and possibly with an open vent stack to atmosphere.  The potable water will likely be a closed system.  During the non-heating season, the house heating system will not cost any heat loss as it can be totally shut down and is isolated from  heated potable water system.  It is quite likely that a stand-alone heated potable water boiler will/can be much smaller than a stand-alone house heating boiler ... making the separation of the two a less costly operating option.

But then, I'm no expert.....

Offline NM_Shooter

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Re: Any experience with indirect water heating for potable and radiant heat?
« Reply #2 on: October 11, 2017, 06:52:13 AM »
OK... I think I am slowly figuring this out. 

It appears that I am going to set up a primary loop around my boiler.  Sort of a loop with a manifold.  This water will be very hot.  Likely 190 degrees or so.  This loop will have a take-off to treat the hot water storage tank heating as a separate zone, but one which is served with a circulator pump and not a zone valve. 

Additionally, off of the main boiler loop, I will have (at least one) temperature mixing valve to downregulate the temperature of the water which runs to my individual radiant heat zones.  I can temper that down to 120 degrees. 

The aquastat from the water heater tank appears to be treated like any of the thermostats in my house.  The only difference is that the heating zones turn on the boiler, primary loop pump, and the zone valve.  The hot water tank aquastat turns on the boiler, primary loop pump, and the hot water tank loop pump. 

Now I just have to figure out if the cheapy caleffi mixing valves regulate temperature, or if they only mix water and the output varies widely with the input temperatures.

Meanwhile, it is getting colder outside.   :o 



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Offline Patrick

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Re: Any experience with indirect water heating for potable and radiant heat?
« Reply #3 on: October 13, 2017, 06:41:49 PM »
I have a boiler system I designed and built I use a primary loop and have 6 zones all separate pumps and 2 different temps.I use a taco control which is what controls the pumps so when the t-stat calls for heat it turns the pump on and tells the boiler to fire the max and min  temp is set on the boiler . To lower the temp at the manifold I use taco mixing valve which is just like a shower valve and they take some return water and some loop water and then send that to the zone mine are manually adjusted. For your water heater just think of it as its own zone you can also set this as priority which then shuts other zones off if heat demand is too high and will send all energy to the water heater. Boilers are usually not set higher than 180 f your questions where a little non-specific but I can get into more detail if you like .Supply house is a great place for boiler parts,valves controls etc i think they have some videos explaining some of the components as well.It can get involved good luck!

Offline JRR

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Re: Any experience with indirect water heating for potable and radiant heat?
« Reply #4 on: October 14, 2017, 08:54:38 AM »
Patrick, you sound like you have blazed the trail.   Are those pumps "rotor" or "centrifugal"?   And did you install on the supply side or return side of each loop?   Thanks for info.

Offline Dave Sparks

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Re: Any experience with indirect water heating for potable and radiant heat?
« Reply #5 on: October 15, 2017, 11:17:03 AM »
I use the DC version for Offgrid. It is the El Cid pump and it uses a sealess shaftless bearing. The rotor floats in the chamber and is magnetically spun.
I know Taco makes a similar version but I do not know abouts Patricks model. This system is controlled by a small 20 watt solar panel that turns on the pump to the solar hot water collector panel. A thermostat then turns on the other El Cid pumps that run different loops. The back-up is a 50 gallon propane water heater with a parallel collector and a hydronic loop in the tank. We rarely use the propane as the woodstove is cheaper than going to the gym :)
« Last Edit: October 15, 2017, 01:36:35 PM by Dave Sparks »
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Offline Dave Sparks

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Re: Any experience with indirect water heating for potable and radiant heat?
« Reply #6 on: October 15, 2017, 01:37:08 PM »
I use the DC version for Offgrid. It is the El Cid pump and it uses a sealess shaftless bearing. The rotor floats in the chamber and is magnetically spun.
I know Taco makes a similar version but I do not know about Patricks model. This system is controlled by a small 20 watt solar panel that turns on the pump to the solar hot water collector panel. A thermostat then turns on the other El Cid pumps that run different loops. The back-up is a 50 gallon propane water heater with a parallel collector and a hydronic loop in the tank. We rarely use the propane as the woodstove is cheaper than going to the gym :)
"we go where the power lines don't"