Modern hot water radiators - what do I need?

How big are the zones? If they aren't huge, a Monoflo system might work well and be easier to install.

How much control do you want? Do you prefer a wall thermostat or a control on the radiator?

Different names for these valves, some call them lock shields, some call the convertible valves. This 220 convertible out of the box it is a valve that can be used to shut off flow by turning the white cap.

Various types of actuator heads are available to add on.

Zone 1 two bedrooms? do you want individual control?

Zone 2 all three on one zone

Zone 3 do you want 3 controls?

There are a few different piping options homerun, series, parallel, monoflo.

https://www.caleffi.com/sites/default/files/media/external-file/01034_NA.pdf

You can overdo the zoning . If you do a heat loss and size the piping and the rads right all you should need is a balancing valve on each rad. The only reason for trvs is if you suspect some rooms will overheat. Trvs will not give you more heat but can reduce overheating

It better to size everything than to fight with TRVs and balancing should only be minor adjustments.

It's been a few years since we did an Idronic issue on zoning. Some ideas and piping options here.

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_5_NA_Zoning%20hydrionic%20systems.pdf

Idronics issue 36 in the works looks at more options, here are some teasers.

Not all heating systems are supposed to be purged to get the air out. The parallel return two pipe and the reverse return twu pipe systems are designed to let the air out of each radiator using a manual vent at the top of each radiator. Installing one valve on each radiator will allow you to control how much heat is released by that radiator by partially closing the valve on a radiator, that radiator will produce less heat. It has worked for many years and there have also been many failures in balancing system using this design. The key is proper maintenance, like exercising the valves at least once a year. Leaving a valve in the full open position for 40+ years and expecting it to work perfectly one day in the far future is not always the best plan of action.

Another thing that the one valve design offers is the fact that you can close off the flow to one radiator but you can not remove that radiator from the system with only one side of the radiator shut off. You must close off both the inlet and the outlet of a radiator in order to remove, it and still maintain water pressure sufficient to operate the heat in all the other rooms.

You actually need to think about how you want the system to operate. With only one radiator calling for heat, the boiler will operate. That is called micro-zoning and that can lead to several problems including short cycling of the burner and circulator. Individual room thermostats can get expensive and may add to the difficulty factor when trouble shooting a no heat situation. For example I had an electrician destroy a zone control by trying many different combinations of wiring and pulling out and swapping plug in relays, when there was no heat in one of the zones of his home. When I arrived that evening, I found a frozen pipe on the problem zone. Now he needs a new zone control and to pay me for thawing out a frozen pipe. Luckily the pipe did not burst. So he has heat that night with that zone circulator operating on one of the other thermostats and working relays left in that control.

Keeping things simple is often the best design, then use old school methods to regulate the room temperature as needed. I find that placing the wired thermostat in the coldest room will allow that room to get comfortable, the other rooms that overheat can then be regulated by restricting the water flow to the radiators in the hotter rooms.

If you are designing the system from scratch, you should just do a room by room load calculation and install the proper size radiators in each room. That is the best way to balance the system. One size radiator for each room is not always the best design. Select the radiator to match the room's needs.

220, 221, whatever it takes! 🤣

I would avoid this idea. Some day a new boiler will be needed and someone will decide that reversing the the direction of the water thru the system is easier that running a pipe about 3 feet longer in order to save a few dollars. At that point the oversized lower temperature radiators will become the hotter radiators and the correct size radiator when it was first on the loop, will not get warm enough to heat that room. Baseboard radiators are the only radiators I would recommend using the series loop, and as long as you don't go over 65 to 70 feet of aluminum fins in a loop, then you don't really need to oversize anything based on a lower water temperature. here is one example of wanting to reverse the flow years after system was installed

Another reason not to series loop radiators is TRVs can be added easily.

If you are doing a modcon or heat pump, I would vote for KISS.

Home run all rads to a manifold with no controls on bulk of rads and TRVs only on bedrooms. You can adjust the flow at the manifold, so local valving on rads without TRVs is not really needed.

Single deltaP circ controlled by a thermostat in the main living space.

The idea is to oversize the rads in the the rooms with TRVs a bit so they will be satisfied before the house thermostat turns off.

Set a decent outdoor reset curve on the modcon and you'll get nice long runs at low fire. Best of efficiency and reducing wear and tear as it minimizes cycling.

@Steamhead I've done both and find the home run is faster. Yes it is a lot of pipe but since you don't have to deal with fittings it is a quicker install. It also means no buried fittings, so much less chance of leaks.

If you have a larger place or multiple stories remote manifolds will save a bit of pipe. Still the same setup though. Single delta P circ to feed all manifolds, all rads are home run to these manifolds, TRVs on rads in rooms where you want extra control.