Radiant Heat

amhplumb_2

Fellow Wallies,
I have a question regarding some radiant heat that I installed in my bathroom floor. I do a lot of Hydronic heating, however, the majority of my jobs are with cast iron rads or copper fin, however am using PEX now! Anyway, in my own home, I removed and replaced a mud tile floor in my bathroom and installed some PEX for radiant heat in the floor. The area served by the radiant heat is is about 3 ft x 8 ft. The room is actually 9' x 9', but that was all the floor area I could use for it (vanities & cabinets!). I supplented with a 2' section of CI baseboard and tied it into the existing hydronic system. My question is, should I get a tempering valve and circulator and tie it into my existing hydronic system, (I used the PEX with the oxygen barrier.) Or for that small section, could I just tie it into my domestic hot water heater (I have a 50-gal gas with a recirc system.) Any thoughts, practical? energy usage? etc.

Al Letellier_9

bath radiant floor

I guess it would depend on how you plna to control that room. Will it be attached and run off an existing zone, or will it be a separate zone? In any case you should use some sort of mixing device to limit the temp sent to the floor. You can cause damage to the floor (and the underlayment) if you run too high a temp. I believe all bathroom should have their own zone, especially with radiant. You want that room and floor warm when you step out of the shower or bath, so I would suggest a separate zone with a mixing valve and its own circ and t-stat. A stat with a floor sensor will add comfort and control year round.

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Ken_40

mistaken double post - see below

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Ken_40

Here's a trick I use successfully...

We would slow the flow through a "mixed zone" to a point that would have the HWBB or CIBB "see" the supply water at a boiler max of 160F on a design day (potential) and have flow so slow as to have most of the room's BB have a 40-degree dT - resulting in an entry into the radiant (typically the first few feet - under a window or on an outside [coldest] wall) first, then the second pass, etc. causing a dT of ~ 60-degrees. Since most homes never see 180 output - and cannot ever see that in the most common layout with a mod-con, a hot spot on the radiant is possible, but un-impacting - because it would be on the wall edge - where no one ever "rests," and with a 4-dollar balancing or circuit valve, setup is simple and the results outstanding.

Let us know what you finally do.

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scott markle_2

ovetrop

Oventrop makes a valve that does essentially what ken is suggesting, It works like a trv but senses water temp instead of air. As water temperature rises flow is restricted, creating very low flow rates with very high delta T's if necessary . It is only recommended for small areas, this seems like a good solution especially if floor is not sensitive to higher temps and as ken suggests water is tempered by CIBB.