TRVs on gravity conversion -- practical issues

Mark Biro

Thanks, Paul, for your help.

I figured the joint had better match real well, and the best fit would be the entire factory-supplied item. Can't just wrap it up in Teflon tape and dope. ;-)

Mark Biro

TRVs on gravity conversion -- practical issues

I want to express gratitude for the discussions I have followed on the Wall over the past year. They have generated fervor in the Fall air here in Minnesota.

Our old gravity boiler wants conversion.

And the radiators (cast iron) have also put on the cloak of righteous fresh paint, and are eager for full immersion baptism into the realm of the TRV -- Wall homilies have won them over.

However (newbie questions!):

1. MUST the new TRV tailpiece be used? That is, must I persuade the old tailpieces from the existing radiators? (Ugh!) They DO seem to match up well to the Danfoss TRVs just as they are. Is there more than meets the eye?

2. Would it be OK to re-assign the gravity piping? Not that the tail should wag the dog, but could the old supply become new return, and old return become new supply? Why? Because all the supply risers lead to the outside corners of the rooms, and I see that the whole addition of TRVs would be cleaner with valve-mounted sensors in the open air, on the current return side. (Hope this makes sense.)

Thanks very much!

Paul Pollets

TRV valve bodies

I'd recommend using the new tailpiece and union nut from the TRV, rather than reuse the existing spud. Ground joint unions must match exactly or there will be leaks. A special radiator spud wrench is used to remove the tailpiece (spud).

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Mike T., Swampeast MO

You might get really lucky and find that the existing tailpieces mate perfectly with the TRVs. Much more likely however that they just fit reasonably and will never seal properly.

TRVs are directional with regards to flow. You'll see an arrow on the body indicating which direction they must be installed. Install them backwards (suprisingly easy) and you'll be treated to a quite loud "bang! bang! bang!" once they near setpoint and begin to throttle down. That said, the TRV can be on either supply or return side as long as the water flows in the proper direction.

Since nearly every standing iron rad will use some sort of angle TRV valve body however you're forced to place them on the supply. Every TRV body I've seen has a flow direction from the threaded (or sweat) connection to the union connection--this means the only possible way to mount on a rad is the supply side.

You can of course reverse the supply/return connections at the mains, but particularly with a gravity conversion, that's a lot easier written than accomplished.

If you don't have room for the operator (or it will be in an inconvenient or unsuitable location) you can also use remote sensing and/or remote adjusting operators. Don't forget that self-contained Danfoss operators should ALWAYS be installed horizontally. If you install them vertically they will not properly sense room temperature. The Danfoss "side mount angle" TRV bodies are typically used on iron rads with self-contained operators.

Mark Biro

TRV mounting, options

Thanks, Mike, for your help, and for expanding on TRVs. I see them on the radiator's supply side in the literature, but have been in the dark still for the bases for it. Such a newbie, so much to learn... and sometimes so little to go on.

I'll just watch the arrow on the TRV's side. ;-)

I feel silly asking about swapping supply and return. I mean, these are not directional tires. Nor Monoflo or something else directional, heating related. Maybe I guess that crud may be caught at joints, and be blown loose if all flows another way? What black crud I do see, though, when freeing joints, is tight, bonded.

The truth is that the boiler is gone. (Was coal-fired, converted to natural gas in the '50s, I think.) Now, only four 1-1/2" pipes terminate above my head, below the joists -- of course, two pairs of parallel piping.

I understand your last paragraph about TRV remote dials and temperature sensors. Very cool. I was, and AM, prepared to mix and match valves and operators -- for example, where corners are insanely tight. I want to simplify, rather than get ignorant clever, if you know what I mean. When all radiators had been removed late last week, and could be turned topsy-turvy, and I saw all the supply risers run into *(&*( corners, and there is no boiler nor near-boiler piping... thought we might have been handed a simplification.

Thanks again for your help!

Mike T., Swampeast MO

If the majority of your supplies are on the "problem" side of the rads, just reverse supply/return in the near boiler piping.

Mark Biro

Spud wrench, the TRV's friend

Mike, thanks again for your thoughtful help.
I appreciate it.

I have now been making friends with the spud wrench, with gratifying results. I guess I got off on the wrong foot with fasteners in metals, 40 years ago, with Honda bikes and a Corvair engine rebuild. Am now loving this cast iron. :-)

Thanks again!

tim smith

Regarding TRVs & old gravity system

Just a footnote, you may very likely find that once the trvs are installed, you will still get some heat out of the radiators when valves are closed. You get heat migration up through the return from natural convection. Not a big deal but I make sure to tell clients that the radiator will not stop heating completely so their expectations are correct from the start. Tim