Help selecting a bypass valve for new towel warmer with TRV

iconoclasthero · February 13

I installed a Hudson Reed towel rack with their H-block TRV in a new bathroom. I had been under the erroneous assumption that there was a built-in bypass in the TRV. As of right now, it's the only thing on this heating loop until more progress is made on this remodel, but eventually there will be downstream baseboard heat so I need to bypass this radiator when the TRV is closed.

Apparently that's what the slides in this thread depict, but In looking around for a valve sold for the US market, I've had little luck finding something designed for this (as opposed to zone control or low-water boilers). And most seem to be angled while a straight valve would be vastly preferable. Also, compared to what I found on Amazon UK, they're an order of magnitude more expensive here.

For the the ca. $25 to have the UK item shipped here, I'm inclined to roll the dice on it and see if the 22 mm fitting will seal on 3/4 in CTS copper (225 μm / 0.00886 in larger) and if the quality is acceptable.

Finally, I can't figure out if I want an auto valve or a differential valve.

It's a one pipe system. The supply and return pipes are next to each other.

This drawing is what I plan to do… The presently-removed green baseboard along the outside walls formerly connected to where the supply and return lines met the exterior wall prior to adding the bathroom. I want to add some baseboard to the outside of the bathroom (interior walls) and the bypass would basically go there from the towel warmer before it went to the old baseboard around the outside walls.

IMG_20250213_180508.jpg

mattmia2 · February 13

Is there a reason you don't want the towel warmer to heat whenever the baseboard is heating? Since it is a series loop it is going to be tough to have the towel warmer turn on and off on a TRV without affecting the flow in the rest of the loop.

iconoclasthero · February 13

Well, for one, it's going to be a nightmare to take it apart again. I plumed it with 3/4 in black iron going through the floor above the crawl space and I pro-pressed the last fittings together so… I really do not want to take it back apart.

For another, I would think it would absolutely be preferable to be able to control the heat in the bathroom.

That Danfoss presentation in the other Heating Help thread specifically suggests doing this for baseboards so I don't know that I'm really concerned about affecting the flow in the rest of the loop… either the TRV is open and it goes through the bathroom or it skips it and hits the interior baseboards first when the bypass is open, no?

Jamie Hall · February 13

Is there any hope — despite having gotten ahead of yourself — why you can't pipe it in parallel with the rest of the loop, rather than in series? Believe me, you will thank yourself if you can…

iconoclasthero · February 14

Correct me if i'm wrong, but isn't that what I'm aiming to do, just with a bypass valve in it? But the short answer is, I cannot see any reason I can't if I understand what I'd need to do… there's lots I have room for in that crawl space.

https://forum.heatinghelp.com/discussion/comment/1842451#Comment_1842451

Jamie Hall · February 14

In a sense it is — but the parallel arrangement won't need a valve.

Put a T on the supply line to the rest of that baseboard circuit. Run a pipe to the TRV on the towel warmer. Then from the return on the towel warmer run a line to a T on the return from the first baseboard in the rest of the series loop.

That will steal heat from that first baseboard when the towel warmer is active, but if that is a problem (it won't take all of the heat) put a balancing valve — a simple cheap globe will do — on the line to the towel warmer and fiddle with it until you are happy with the overall balance.

iconoclasthero · February 14

"… a simple cheap globe will do — on the line to the towel warmer and fiddle with it until you are happy with the overall balance."

Shouldn't I be more—or at least as—concerned about down-regulating the supply to that first radiator?

And why did I see a number of posts about needing a balancing valve at a radiator with a TRV? Is that just valve manufacturers trying to sell more valves worth hundreds of dollars (because this is obviously significantly less expensive)?

Kaos · February 14

Like Jamie said, if the baseboards are not in pipe like this:

The only reason for series piping is to save cost for a production builder. You don't need the TRVs for each baseboard, you can set the flow at the manifold to control.

This now gets you individual control of the amount of heat in each room and much better heat balance. The towel warmer also now just becomes another zone and the regular TRV works.

hot_rod · February 14

are you looking for a H valve for a 1 pipe system? Typically they use 1/2 Pex or copper, maybe 3 radiators in a circuit, depending on the size.

They could have TRV in each radiator also.

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https://s3.amazonaws.com/s3.supplyhouse.com/product_files/301241-Caleffi-Product-Overview.pdf

mattmia2 · February 14

isn't the baseboard going to be heating the bathroom regardless?

iconoclasthero · February 14

I like Jamie's parallel idea a lot more than getting involved with a manifold setup. This isn't going to be "rooms," it's going to be one studio apartment with a bathroom that's one loop off the boiler. The kitchen's going to be open to the rest of the area, but I do need to make up for a radiator from a different loop that's not going to be contributing anymore…the wall that's labeled "addition great room" has a baseboard along it, not depicted in the diagram. (There's probably going to be a minisplit to add some suppliemental heat/independent control too.)

There's another thing… the baseboard that was there had that line that all the way back to the source because the other side of the beam was not accessible until I cut the trap door in there. That's not as easy to work in (although neither's the other, but it's not as bad).

iconoclasthero · February 14

https://forum.heatinghelp.com/discussion/comment/1842462#Comment_1842462

there's no baseboard heat inside the bathroom so only from convection from outside if the door is open.

mattmia2 · February 14

if he return is in the baseboard enclosure you could tee the supply off the baseboard element and tee the return in to the return and put a balancing valve somewhere in the loop to the towel radiator. the balancing valve could be an inexpensive globe or ball valve as @Jamie Hall said, it doesn't need to be marketed as a balancing valve

hot_rod · February 14

it is nice to have a towel baron its own zone, you may like it enough to use all year around. However it could short cycle a conventional boiler.

The electric towel bars area nice option on a setback control. Generally 250w and up sizes available.

iconoclasthero · February 14

So if I have this correct in my head, my original idea had been to put a purpose-built differential or automatic bypass valve into this loop as on the left. Jamie's suggestion was to run in parallel, ||, with a globe valve as shown on the right. I'm unclear as to whether the second globe valve (pictured with "?") would be helpful to make sure the bath is getting as much heat as needed.

I'm fairly sure that I could revert back to my original idea by switching the "?" valve to a bypass and plumbing in the dashed red line (though I'd probably need to cut a shutoff in on the return branch from the towel) so that leaves me options.

IMG_20250214_080642.jpg

https://forum.heatinghelp.com/discussion/comment/1842483#Comment_1842483

A tenant renting the studio apartment is not going to get to make decisions like this; the towel warmer's going to have hot water available when the central heat is on and not available when it is off. The person paying for this renovation isn't going to install an electric towel heater adjacent to the hydronic one. The only thing that would be a consideration is adding electric to the existing hydronic radiator…but it's not like I have a significant budget to just do whatever. Since some amount of tenant-controlled HVAC will be necessary, the plan is to make any deficiencies up with a minisplit.

hot_rod · February 14

There are other way to balance a emitter like that. If you know the desired flow you select the valve with that cartridge, a PIV pressure independent balance valve.

Caleffi also has a 230 series TRV called the Dynamical. It has a balance function inside the valve, adjustable. Basically 3 devices in one, differential pressure regulation, preset function, and flow control based on ambient room temperature when a TRV head is added.

However we do not offer the Dynamical version in the US. Probably find it on a UK website.

With any TRV or balance valve a y strainer is a good addition to protect the small passageways.

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Help selecting a bypass valve for new towel warmer with TRV

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