Convert 3/4" NPT to DN15

imaddicted2u

My heating system consists of an oil fired boiler pumping to a supply and return header then to cast iron radiators. The pipes and valves are large since it started life as a gravity system fed by a coal boiler.
Things are getting modern around here, I put a mini-split heat pump in the main living area, There are two radiators in the area. I shut the 3/4" and 1" valves to them. Based on past outdoor temps, There may be a few times a year that I'll need auxiliary heat when the heat pump doesn't have enough output.
I'd like to automate the valves so they open when needed based on temperature. I found some DN spec valves for sale at a good price. Can anyone tell me where I might find bushings that go from NPT male to DN female. I was thinking I would replace the 3/4" and 1" NPT hand valves with DN15, I think that's a metric straight thread. Since the system is pumped now, do you think it's OK to make the valves smaller or should I keep them close to the same size?
Here are pics of the current valves.

pecmsg

Can you put 1) 24 volt motorized valve below?

imaddicted2u

pecmsg said:

Can you put 1) 24 volt motorized valve below?

Thanks for the quick reply, It would be difficult, both rads are fed from different points on the 2 and 1/2" headers and the pipes to the rads are 3/4" and 1" schedule 40 so cutting and threading would be a large task.
The valves I can get have a thermostatic operator fitted on top. They are very popular in Europe. The operator presses on the plunger to open and close the valve to control room temperature.
I'm hoping that if I can find NPT to DN adapters the these valves will fit rigt in with little to no modification.

Jamie Hall

Problem. The fitting which joins the valve to the radiator on those things isn't a threaded connection, it's a union. There is a stub which is threaded into the bushing in the radiator, the other end of which is half of the union. The other half of the union is on the valve.

Both your sample pictures show the same arrangement.

So -- you will have to get the stub out of the radiator, and probably the bushing as well, and find a suitable fitting to put the European style thread in instead. This is not going to be simple...

hot_rod

A bushing would reduce the female port to 1/2”

There is a double nipple, 3/4 BSP x 3/4 npt that would give you make npt.

It might be easer and less $$ to get npt valves?

imaddicted2u

Jamie Hall said:

Problem. The fitting which joins the valve to the radiator on those things isn't a threaded connection, it's a union. There is a stub which is threaded into the bushing in the radiator, the other end of which is half of the union. The other half of the union is on the valve.

Both your sample pictures show the same arrangement.

So -- you will have to get the stub out of the radiator, and probably the bushing as well, and find a suitable fitting to put the European style thread in instead. This is not going to be simple...

Clearly the current union threads into the bushing adapter in the radiator, the other side is a threaded nipple. Yes, I agree, the union stub and nipple need to come out. They went in, it might take some heat to get them out. I think what I'm looking for is a NPT male to DN (metric) bushing so I can thread in the European threaded valve. Just asking if they exist and where I might buy them?

imaddicted2u

hot_rod said:

A bushing would reduce the female port to 1/2”

There is a double nipple, 3/4 BSP x 3/4 npt that would give you make npt.

It might be easer and less $$ to get npt valves?

In the end, I may be looking at a couple of NPT vavles but I can get a bunch of the DN15 for $15 each, so I thought I might just put them on all the rads for cheap. DN20 and DN25 I can get for a couple $$$ more.

WMno57

https://tbwprecision.com/custom-solutions/steel-bushings/
"We, at TBW Precision, use a wide range of machines to create parts of any size and application. Our Brown and Sharpe machine, the TBW workhorses, can ensure higher volume production of steel bushings in a lesser time frame. If you plan to place an order for less than 10000 units of steel bushings, then this versatile Brown and Sharpe will get it done quickly in a cost-effective manner."

WMno57

https://en.wikipedia.org/wiki/British_Standard_Pipe#Pipe_thread_sizes

hot_rod

get one and try a nipple. Sometimes you can get a npt nipple into a BSP
There is no taper to seal, so Loctite us an option 

On the other end is a conical seal and you can find NPT nipples with that cone end

imaddicted2u

Hmm, think this would work?
https://www.britishmetrics.com/details/item?itemid=BH-16356#

hot_rod

Don’t you want to convert the 3/4 female BSP

That fitting looks to be 3/4 male Npt, 1/2 bsp femake

imaddicted2u

hot_rod said:

Don’t you want to convert the 3/4 female BSP

That fitting looks to be 3/4 male Npt, 1/2 bsp femake

I'd like that but don't think there would be enough meat left to convert 3/4 to 3/4, at least not in a bushing. Don't think I've ever seen one that size. Figured I'd have to drop to a 1/2" valve and hope it still gives enough heat.
I think I'll get a DN20 and see if it will jam it into a 3/4 NPT fitting with some sealant, like you suggested earlier. Thanks for that.

hot_rod

A 1/2” valve like that is around a 2.7 Cv, so 3 gpm flow, easily

how many btu/ hr are you looking for?

imaddicted2u

hot_rod said:

A 1/2” valve like that is around a 2.7 Cv, so 3 gpm flow, easily

how many btu/ hr are you looking for?

First let me relay some oddities about this system. I'm kind of afraid to drop to 1/2". Ever since we moved in here, for some reason these two rads seem to throw less heat. Even after balancing and air bleeding all rads, with the 3/4" valves on these 2 rads wide open one got warm at the valve end. All rads at that end of the header, farthest from the boiler, took longer to heat up. The headers are two sets of headers consisting of 2 1/2" and feeds/returns are 3/4" or 1". I replaced the Bell and Gossett NRF-22 pump with a higher flow Grundfos UP26-96 BF and for the first time ever, the whole rad got hot and it made a huge difference in heating the space this past winter. Calculated head loss is 3.4 so the current pump should be flowing about 27.5 GPM. Where the NRF-22 would be around 17 GPM. I increased the pump, in part to satisfy the flow through the bypass line I added to keep the return temp up. With the NRF-22 I couldn't open it and supply heat at the far end of the house. With the grundfos I can run it at half open and the far end rads get warmer.
According to the btu/hr/SQ. FT.EDR of the rads, they should put out 6415 and 9180. By heat loss calculation for the space 2000 and 5000. It's one L shaped room.
There is something off about that one radiator, maybe it's the feed piping. I've wondered if maybe I'll find an orfice plate, something else restricting flow when I take the valve out.
The other thing is, the rads here seem large compared to what I've seen in other houses. I've experimented with cold starting the boiler and the thermostat gets satisfied at between 120 and 130 degrees F boiler temperature and the rads only ever get warm. I go to my brother's house and I can barely touch his rads. If I set the boiler temp up where it should be the thermostat gets satisfied before the far end of the house has time to warm up and the rads don't seem any warmer.
There was a coal boiler here when we bought the house, I burned coal for a year and if the boiler temp would be around 120 degrees F, the house would be smokin' hot, you'd have to open windows and let the fire die down. Maybe another indication that there is excess radiation.
Sorry, a lot to digest.

Jamie Hall

Oh boy. I think that maybe, just maybe, you are applying bandaids to something which needs more examination.

First, how hot a radiator gets is really quite irrelevant. What matters is does the radiation heat the sapce the way you want it to? Comparing two houses can be quite misleading, as one may have larger radiators than the other, for example, and thus rum well on lower water temperatures than the other.

Second, you may have a moderately simple balancing problem -- and fiddling with replacing radiator valves isn't going to help that. You need to step back and look at the radiation you have, the piping, and whether the temperature control in the various spaces is what you want. Then if necessary adjust the radiator valves (or balancing valves if you have them -- you probably don't) to get the heat the way you want it. Note, however, that if some of your radiation is arranged in series rather than in parallel, you may have trouble doing that -- but you need to know the layont of the piping first.

imaddicted2u

Jamie Hall said:

Oh boy. I think that maybe, just maybe, you are applying bandaids to something which needs more examination.

First, how hot a radiator gets is really quite irrelevant. What matters is does the radiation heat the sapce the way you want it to? Comparing two houses can be quite misleading, as one may have larger radiators than the other, for example, and thus rum well on lower water temperatures than the other.

Second, you may have a moderately simple balancing problem -- and fiddling with replacing radiator valves isn't going to help that. You need to step back and look at the radiation you have, the piping, and whether the temperature control in the various spaces is what you want. Then if necessary adjust the radiator valves (or balancing valves if you have them -- you probably don't) to get the heat the way you want it. Note, however, that if some of your radiation is arranged in series rather than in parallel, you may have trouble doing that -- but you need to know the layont of the piping first.

I have no issues with the system and how it's working per se. I have taken great pains balance the manual valve located on every rad in the system, that's not an issue, you can walk from room to room and all rooms are comfortable and heat throughout the house is even. The reason I'm fiddling with replacing valves is only because, as I stated previously, I installed a heat pump and want to automate the two rads in the space with thermostatic valves to kick in as auxiliary heat on the any days where the heat pump may not have capacity to keep up.
All rads are parallel and I'm familiar piping layout. My brother's house needs 180 degree water mine needs 120-130 degrees. So, certainly I have more radiation. What got me looking at bypass and pumps was the less than 100 degree return water into the boiler. The bypass and larger pump helped with that by allowing enough flow to the house and through the manual bypass at the same time so boiler discharge water can mix with the return into the boiler.
I only detailed the system oddities because @hot_rod was trying to help determine if dropping the valve size from 3/4" to 1/2" would still allow enough heat to the rads and I thought more details would be helpful. Other than that, the system works satisfactorily ever since I added larger pump and bypass piping, plus the boiler is protected from low return temps.

Jamie Hall

Fair enough. It would be a lot less hassle to install a simple zone valve on the line or lines to those two radiators, with an equally simple backup thermostat to open it when needed... not very whizzy, but parts are off the shelf and the work involved is minimal.

imaddicted2u

Jamie Hall said:

Fair enough. It would be a lot less hassle to install a simple zone valve on the line or lines to those two radiators, with an equally simple backup thermostat to open it when needed... not very whizzy, but parts are off the shelf and the work involved is minimal.

Both rads are fed from different points in the supply and return headers, it's all schedule 40 pipe, Hard to get at, not impossible but a difficult DIY to deal with. if it was copper, it would be pretty easy. I think I'm going to try to fit in the thermostatic valves that I posted above, in place of the manual valves. The valve dimensions are the same, threads are different. I'll see if it will thread in to a 3/4" NPT fitting. If it will, I jam it in with some sealant. IF not then maybe reducing bushings and 1/2" valves, if there will be enough flow. Most of the time the thermostatic valves will be closed. I have until fall to figure it out.

hot_rod

For what you are trying to accomplish a TRV is the perfect valve to use. It is a proportional, non electric valve with temperature responds, perfect.
There is always a way to build up fitting assemblies. With that union on one end it should be plenty doable.

When you have odd, mis matched or straight threads a Loctite thread locker is what to use,not a pipe dope type product.
The lockers actually glue the pieces together.

When they assemble ball valves, that is how the two halves get assembled, typically a green Loctite type product..There are many choices of thread lockers, some versions can be disassembled, other versions are permanent and you typically damage the threads trying to un-do them, or distort the fittings and nipples.
Good luck with the project.

imaddicted2u

hot_rod said:

For what you are trying to accomplish a TRV is the perfect valve to use. It is a proportional, non electric valve with temperature responds, perfect.
There is always a way to build up fitting assemblies. With that union on one end it should be plenty doable.

When you have odd, mis matched or straight threads a Loctite thread locker is what to use,not a pipe dope type product.
The lockers actually glue the pieces together.

When they assemble ball valves, that is how the two halves get assembled, typically a green Loctite type product..There are many choices of thread lockers, some versions can be disassembled, other versions are permanent and you typically damage the threads trying to un-do them, or distort the fittings and nipples.
Good luck with the project.

Thanks for the input. I found some adapters that go from 3/4 npt to 3/4 bsp. Takes up more space than a bushing so I'll need to be sure I can make room for it. I think it's best to go with what we know and try to stick with a 3/4" valve. I like the idea of fitting it together with the loctite.
Hopefully it doesn't resist coming apart too much.




Here is the valve on Amazon...simple and cheap...and I like cheap...lol.
https://www.amazon.com/Qezodsx-Thermostatic-Radiator-Automatic-Temperature/dp/B0BW31J115/ref=sr_1_4?crid=32I1TXMD7MB05&keywords=dn20+thermostatic+valve&qid=1687572657&sprefix=dn20+thermostatic+valve,aps,164&sr=8-4

hot_rod

I don’t recognize the brand, a knock-off I suspect

That fitting is called a nipple extension or extender. That version also combines the two threads.

A 3/4 valve like that is typically around a 3 - 3.5 Cv, adding a bushing to keep the length down would not reduce the flow all that much. Especially for a single radiator use