Radiant heat from hot water tank

alcraig

I'd like some opinions on ways to add another zone of heat to my home (preferably radiant floor heat). In reading Dan's article about hybrid hydronics (<a href="http://www.oldhousejournal.com/magazine/2003/february/hybrid_hydronics.shtml">http://www.oldhousejournal.com/magazine/2003/february/hybrid_hydronics.shtml</a>), he recommends not add a radiant zone directly off a steam boiler. However, I have a home that has its domestic hot water tank circulating off the steam boiler. If Dan says it's too "dirty" to use a steam boiler with radiant heat, does this mean that it's also a bad setup to have my domestic hot water tank tapped off the steam boiler (which is the original 1936 setup)? Do we have "dirty" hot water?

But if it's fine the way it is, can I also tap off the hot water tank for radiant heat (plus adding a mixing valve to lower the temp)?



Thanks,

Al

jpf321

i don't think...

that you are using your actual boiler water .. but that your domestic hot water (DHW) is entering the boiler into a pipe or "coil" which is submerged in the hot and dirty boiler water. but that is kept separate by way of the walls of the coil from the hot and dirty boiler water .. this can be proven if you like by completely draining the boiler water and see if water still comes out of the hot side of your faucets .. this method of heating DHW using the hot and dirty boiler water is called a "tankless HW coil". straight boiler water is usually much more unpleasant and i wouldn't recommend washing dishes or clothes with it :-)

alcraig

I see...

thanks for the clarification.

In that case, is it possible to tap into the DHW storage tank to circulate through a radiant floor heating zone? Since it's PEX-AL-PEX, it shouldn't contaminate the DHW.

jpf321

i'm sure...

that is possible .. but whether that's the best course of action is a question better left to someone other than myself. you may have other options. i can't say that running all your DHW through a PEX radiant heating system will maintain the potability of the water. there may also be Building Codes which prevent it. i just can't say if the solution is a wise one. is it possible, certainly .. you need a circulator pump with a takeoff for the PEX and then a return into your HW tank. the other question that will come up is whether you can make enough HW to handle both the radiant heat system, which is designed to extract as much heat as possible, and the showering, dishwashing, laundry needs of the household .. right now your HW tank may simply be storage, you may need to actually turn it on.



let's see if anyone has any opinions...since mine aren't based on first hand experience.

Charlie from wmass

Bad idea for a couple of reason.

Reason 1. Legionela. this can occur with stagnant water and the radiant loops will be stagnant when not warming the room. Reason 2. You will have a loss in hot water capacity when you are trying to warm the room.

What may be a better answer is a small indirect water heater pulling off the steam boiler acting as a heat exchanger for the radiant zone. this would act as a seperator between the steam boilers water and the radiant controls and tubing.

Answer number 2 is install cast iron base board in the room for spreading out the warmth over a wider area than a radiator does.

The fact radiators have a very close heat curve to radiant heat makes them my favorite choice if you already have a steam boiler. K.I.S.S. keep it super simple.

alcraig

What do you think

about a "Open Direct" system as described by Radiantec? I have plenty of capacity in my tank so the first issue you raised is address by their design. They run the DHW through the zone before it goes to the fixtures.

Here's a link to their design:

http://www.radiantec.com/systems-sources/open-system.php

Charlie from wmass

Put down the mouse and walk slowly away from the computer.

When it is safe turn and run. That is my opinion of that concept. It is totally against the protection of potable water ideas that form the plumbing codes.

Is it done through out the world everyday? Yes!  Is it safe? HECK NO!

WHy they can get away with trying to peddle this I do not know. Could be they are from an unregulated region where codes are loosly if ever enforced. Not all ideas found online are good ideas.

jpf321

but they say.....

Charlie, you are no doubt correct, however, they have a special section on their website stating that their "concepts" are code approved.. http://www.radiantec.com/codes-approval/ ... they only thing I can think of is that they are pumping the return from the radiant back into the HW "heater" where theoretically it will be heated above 140degF which should, again theoretically, kill off any bugs. But I would not subject my kids to the possibility of anything if it was my house. 

alcraig

Look at it closer.

There is no stagnant water in this design. Each time a hot water fixture is opened, the entire system is circulated. The whole circuit is built with potable safe components and the water is simply traveling through a longer (the radiant portion) set of piping.

Other than someone coming later and not realizing the zone is to be treated as potable DHW (and possibly screwing with it), where is the suspect part of the loop?

jpf321

i don't see that....

i don't see that each time the hot faucet is open the system is circulated .. i see that there is a circ pump right of the cold water .. which presumably runs when there is a call for heat in the radiant system. when there is no call for heat .. the system is not "evacuated" .. the pump stops running and the water in the radiant system stops running... and becomes stagnant (and cold)



what i do also see is that when there is HW use, such as a shower....the cold water will run under the floor first and then enter the HW system...which seems like a silly way to heat a floor (with new cold water) although it is being directly mixed with HW Tank water.



i'm going to leave this one to the folks with licenses .. being that the cold water is running through the floor prior to tank, i don't see how this is much different than all the miles of pipe that it takes to get it from the reservoir to my house in the first place. or really much different than water sitting in the pipes in an often unused guest bathroom ... but be aware that your toasty warm floor might drop to ~53dF if a shower is being used at the same time.

Charlie from wmass

I live in Massachusetts so I go by our codes.

The drawing has the water being used for heating and potable use with no seperation. WHat people want to do in Vermont is their choice. I guess the cold water flushing out the slab when hot water is used is ok by some people. It is not ok by me nor would I want to face an inspecter with this kind of nonsense. I can heat my house with a cut open 55 gallon drum and burn used tar roofing but I would not advise you to expect it to meet code.

Unknown

Radiant Heat from a Hot Water Tank

When a Pro with Charlie's experience speaks so emphatically, it pays to heed his advice. I sure do.

You mentioned you wanted radiant floor heating. You can't do this with 140 degree water so how are you going to modulate it? Add cold water? Where does the extra water go?

As for the Legionella- In Europe there is thought that water heater temperature should be raised to 160 degrees as it has been pointed out that not all of the water in the tank necessarily reaches 140 degrees. What you are proposing to do is make an ideal environment (warm and stagnant) for legionella and then hope that all bacteria are killed in your 140 degree tank.  If you have had the experience of sharing the hot water with showering teenagers, you will immediately see the fallacy of this proposal.



As for "codes" - I read the webpage you linked and only 2 phrases on the whole page mean anything. "Since it is impossible for a manufacturer to know the particulars of all state and local codes, it is your responsibility to make certain that your proposed heating system complies with them." "Only your local code official can approve your plans."  (Their emphasis, not mine)  This should be a "red flag" that you aren't likely to get it passed by your local inspector. Always keep in mind codes (especially for potable water) have been put in place for safety and are usually the result of someone suffering an unfortunate accident. To circumvent them you do so at your (or your family's) peril!

- Rod