Max Water Temp in Concrete Slab

Mike T., Swampeast MO

Only one I've specified (for a relative and for DHW use) is a Rinnai based on my research and understanding that it's <I>awfully</I> similar to a mod-con. Checked out the unit and installation and it sure looks and acts like one...

Of course using <I>any</I> "water heater" as a space heating appliance is rather contentious.

Befuddled

Max Water Temp in Slab

What is the max water temp you can run thru a concrete slab? And why?

jp_2

less than 170F

experience told me 170F was too much by the explosive sound the slab made when it cracked! who's shooting guns in the house? so much for on-demand recirculating water heaters.
luckily it was an experiemental project.

seems to me that mid 80's floor temp on cement like surfaces feels plenty warm.

hr

140F

seems to be the number I see in RPA and other guidelines. same for gyp pours. Unless you get an approval from the manufacture otherwise.

hot rod

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Mike T., Swampeast MO

How can you turn that experiment into a general denouncement against on-demand water heaters? The difference between such and mod-cons isn't much...

You could do the same thing with a mod-con if you paid no attention to proper sizing of the boiler to the load; proper piping techniques or proper flow calculations.

jp_2

in simple principle yes,

they both take varing water flows and heat to a set point, but the similarity stops there.

1.) on-demands that I know of do not condense

2.) units like the bosch have no electronic controls, only mechanical

3.) the bosch's efficiency is around 80%

4.) have not heard many people here talk highy of such a set up....

hr

How the heck do you get 170

from an instantanous water heater? MostI see have limits around 140.

Also you must have had a lot of horsepower to shock a slab into that type of rapid cracking.

hot rod

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Mike C_3

here comes my 2c

Ok My Noritz at the shop goes to 167* I believe.
Also the Rinnai has mid 80's effeciency
We did a Noritz at a house: Hung-Pex (customer did not have any kind of reflective insulation or anything installed, nor transfer plates), DHW(via tempering valve)
customer was only unimpressed with one night where it got to about -5* In a bedroom 15x20 big french door and 2 other big windows on either side. They had to put on an extra blanket. Other than that he loves his heat. His gas bill is exactly where he wants it.


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hr

Sure a simplistic radiant system

can heat a space, as you mentioned, most of the time. Even a campfire in the basement would heat the home.

For the additional cost I think a nice mod con with transfer plates and proper insulation is hard to beat. And the ROI is there.

Many of us have installed mod cons in replacement of 80% boilers or heaters and see fuel savings of 30% or more. Running the lowest possible supply temperature with outdoor reset, keeping them seeing cool return temperatures AND the modulation feature alll add to this efficiency. Plus they are listed as a heating appliance, not a water heater.

Your 80% instantanous water heater customer may not know what they are missing Especially on design days when the heat is needed most.

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jp_2

hotrod

the whole story;

the slab was 1.5 inches gypcrete, slab was cold, it was late, i was tired but wanted to see some heat. the crack occured on an outside wall, tube parallel with the wall. so it was as weak as you could get.

what I thought was a new unit turned out to be re-conditioned, apparently NOT re-conditioned enough, it has problems, someday I'll get around to taking it apart and fixing it. seems those units don't deal well with recirculation water.

I can see where the simpler units don't expect to see incoming water at 70F or higher.

jp_2

condensing?

so you are saying the rinnai condenses?

they're "all" water heaters.......

Mike T., Swampeast MO

Not sure. Temperatures are certainly in the "condensing range" as its max supply temp (with special control) is 140°F.