# Let me pick your brain



## OldSchool (Jan 30, 2010)

Got a customer that wants to use his instant hot water tank to do both his infloor and his domestic...

So how should I go about this.... normally I use a boiler with an indirect tank...

So what would be the best way to go about this?


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## Bill (Jun 17, 2008)

Not sure, but here the domestic hot water and any water used in heating MUST be separate.


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## Lifer (Nov 23, 2010)

Don't ..
lol that's the best way just don't, we in the past have had co. with 60 gal hwt's used for in-floor and the only benefits were low start up costs . But with the price they were paying to keep all that water hot , they lost all savings fairly quick.

As far as i can see the only way you should do in-floor and domestic off the same unit would be through the use of a plate style heat exchanger, a few pumps and a tempering valve. But i think you would be better off having a wall hung boiler for heat and an on demand tank-less for domestic.

Just my .002$

Lifer...


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## hydronicsbob (Oct 6, 2010)

*couple of things*

first thing - the whole domestic water and stagnant water sitting in your heating zone = disaster (keep the two separate)

2nd thing - pressure drop through tankless water heater is usually high (must get pressure drop and size circulator properly) I explain it like this. In a tankless you usually have 45# of municipal pressure pushing through a small amount of water, in a heating system you have to size a circulator to "produce" the pressure to move water through the heat exchanger.

They do make a unit that has two heat exchangers but I think the domestic load is small. anyway a couple of things to think about.


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## dclark (Dec 12, 2010)

As others mentioned, check your local codes regarding circulating domestic water through a heating system.
You cannot do that here, with few exceptions.

Quietside boilers are designed for your application. I've never installed one, but have looked at a few installations. 
There are also other mfgs that have comparable units.
These have built in heat exchangers so you are not sending domestic water through your heating system.
Check your loads (Heat loss, and domestic demand).
Ontario winters are cold, heating demand might take away a lot of your domestic capacity.

I've installed one Rinnai with a 12 Gal electric tank as a buffer, feeding a flat plate heat exchanger to radiant. The heating side involved one Grundfos 26-99ss pump (to pump the Rinnai), and two Grundfos 15-58s to pump the flat plate and radiant. I didn't wire the elements, but used the aquastat to control the 26-99 which pumped through the Rinnai. Big pump was needed because the Rinnai has a crazy high head loss.Rinnai The 15-58 pumping to the flat plate was on outdoor reset, injection control (tekmar).

Would I do another that way? No. I didn't want to do this one.
It seemed like a long way to go (read that 'expen$ive') to warm a basement slab with an 80 something percent unit, but the owner did his own research. Cough.

Another option would be to use the Navien heating box. Basically the same thing that I did with the Rinnai,hwt and flat plate, but in a neat package.
I've only repaired these, never installed one. The 2 I've worked on were paired with Rinnai units.
Very noisy Armstrong pumps in them though (or at least they were).
Would I suggest to a customer or try to sell one of these? No.

My brain tells me that anytime you pass water through a secondary heat exchanger, you've had to heat the primary water to a higher temp than is at optimum efficiency. ( To get your heating water to target temp, say <115F if you're on radiant, you night have to heat your primary water to 140, or more, depending on the size of the exchanger and flow rates). Higher operating temps normally = higher stack temps = lesser efficiency?

My suggestion would be to try to head them towards two separate units, dedicated. Especially if the heating side is radiant.
Mod con boiler on outdoor reset, and Navien or your choice of an on demand tankless. 

If they are stuck on having one unit, I'd try to head them towards doing it your way, Boiler heating domestic through an indirect coil.

Adding my $0.03 (higher cost of living on the west coast).

Don.


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## Scott K (Oct 12, 2008)

*Heating Help forum*

There are a few points worth considering in this thread on heating help from today: http://www.heatinghelp.com/forum-thread/134159/Boiler-Swap


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## plumber666 (Sep 19, 2010)

Was looking at a new line of heaters that do this job well. They're a combo domestic/heating tank, built in heat exchanger and circ pump, with the footprint of a 50 gallon tank. Price points not bad too, around three grand for a 200 MBTU unit. Great controls, too. HTP Advanced Heating Products. I'm sure they have a wbsite. I can get them in BC via Bartle and Gibson.


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## beavercreekhc (Mar 15, 2010)

Install a Weil-McLain with a dhw easiest way to do it


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## sikxsevn (Jun 23, 2009)

An earlier poster mentioned Navien, I just had a couple things to say, though it's slightly off-topic. The company I work for used to install Navien tankless water heaters, and we had all kinds of problems with them. Out of the 60 something units
We installed, we had problems with about 40 of them. At least they had great tech support, and they would overnight us whatever part is was that needed to be replaced. However, we were having to go back constantly to the same units to replace the same broken parts repeatedly, in some cases we had to just replace the units with something else. After replacing about 15% of the Naviens we installed were warrantied at our cost to the Eternal units we are using today. 

Navien claims to have made a revised model with better quality materials and backs their units with a great warranty, etc...

Take it as you will, just food for thought


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## Ishmael (Dec 9, 2009)

I installed one of these combination units once. The owner has been pleased with it:

http://www.embassyind.com/onex-condensing-boiler.asp


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## amh112181 (Sep 3, 2009)

*Water tank*

I did not insatll it. But I have seen a Bradford white 50 gal tank with 4 taps on the top 2 were for domstic 2 said space heating. If your load was small enough you could use one of those. I was there for the propane company to light it after a runout. It was hooked to a in slab radient. The lady that lived there said it took almost a day to heat up.


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## Plumbworker (Oct 23, 2008)

use a thermostatic mixing valve on outlet of tank cut in high temp tee feed below mixing valve on hot outlet install properly sized flate plate heat exchanger with variable speed mixing circulator and sensors. Run primary side of heat exchanger return line to bottom of tank..then pipe the secondary side of heat echanger with pumps air separator auto fill and expansion tank etc.. i did one of these for a guy a year or so ago like that with a taco x block mixing station you should look into this device..


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