Single loop or three loops

DeathValleyDog

So the heating system I'm installing in a small home will use radiators (probably Runtal) and the current plan is to have three of them in the living room, which is about 500 square feet with a vaulted ceiling and an open loft. The calcs have all been done on the BTU output requirements for the room, so I'm good there. All three radiators will obviously be part of the same zone.

The question: Does each radiator need to have it's own dedicated loop? Or can I get away with a single loop, where the tubing runs to one radiator, then to the next and then the next, and then back to the boiler? And if so, would it help to have the smallest BTU output radiator of the three be first in line? I'm just thinking if it went to the biggest one first, the water would be less hot by the time it got to the last one.

Or am I overthinking this or misunderstanding something? (wouldn't be the first time )

hot_rod

usually no more than 3 in series. If you can use a H valve they are available with an adjustable bypass to help balance and not starve the last one.

Big Ed_4

You mean daisy looping , I am not a fan .. I would run one line with diverter tees . Say one 3/4" main loop , for each radiator use 3/4x1/2x1/2 tees 1/2 between the tees with 1/2 risers .. The largest distance of 1/2 between the tees , the more the movement of flow into the radiator .. Min the the length of radiation . On the risers make sure a bubble with rise to be bleed out ? Can you work this under the radiators ?

DeathValleyDog

Big Ed_4 said:

You mean daisy looping , I am not a fan .. I would run one line with diverter tees . Say one 3/4" main loop , for each radiator use 3/4x1/2x1/2 tees 1/2 between the tees with 1/2 risers .. The largest distance of 1/2 between the tees , the more the movement of flow into the radiator .. Min the the length of radiation . On the risers make sure a bubble with rise to be bleed out ? Can you work this under the radiators ?

I think I'm understanding what you're saying about the diverter tees: So the water flow essentially gets split, some going through the radiator and some not. Basically working similar to the H valve that Hot_Rod mentioned above.

Not certain what you're saying about bleeding out.

DeathValleyDog

hot_rod said:

usually no more than 3 in series. If you can use a H valve they are available with an adjustable bypass to help balance and not starve the last one.

Copy all of that. Would you recommend 3/4 for the main line if I used the H Valves, or could I get away with 1/2 ?

Big Ed_4

The you don't want to trap air in the risers leading up to the radiator .

Daisy looping you would use radiator diverter valves . I find it tricky to get all radiators evenly heated with diverter adjustments .

DeathValleyDog

Youngplumber said:

Pipe size depends on gpm and btus. 

You probably want 3/4.

The room calcs came out to about 20,000 BTUs, so the three radiators match that. I read somewhere that a loop of 1/2" PEX can do 23,000 BTU's

I know that ideally there are other factors to consider, but generally does that sound right?

EBEBRATT-Ed

@DeathValleyDog

Take your total BTUs for the living room and and divide it by 10000 this will give you the GPM you need. 1/2" will do 1.5gpm, 3/4 will do 4.5 1" will do 8.0 gpm

TAG

Small home and the living room needs 20k BTU's ?

If you look at the Buderus panel radiators or others that look like them you will see they have an internal pipe and valve set up with a thermo head option. You can also buy a chrome diverter valve that attaches to the bottom of the units two fitting that allows one pipe operation. That's what Hot Rod is showing ...

The panels come in two thicknesses w/ the thicker being higher outputs -- the thermo head adjusts the flow from the one pipe loop into the radiator depending on room temp need .... they work great and you see them all over Europe.

I have used them in many of my personal projects .... my memory was 1/2 Pex is good for at least 12k. I can't remember how much. With manifolds and Pex I did a whole big house with them that previous had forced hot air. It was a mix of the panels and radiant. Most rooms had two radiators ...some had three .... I just looped the pex around and used one manifold space for each room. The diverter just pulls what it needs from the loop. I sized them for lower temp water.

Have also used Runtal --- they are more difficult. Since they don't have the internal piping or thermo head --- it has to be all external. Obviously if you use one pipe w/o any diverter the first radiator is going to take the heat and the next will get colder water .... figuring all of that is above my pay grade.

With my Runtal towel racks -- used a thermostat and valve on the manifold loop/zone ... but, this uses one space for each radiator. Have also used tall thin Runtal units in retrofit situation where I did radiant in an old house and the floor was not enough -- again ... direct piped to the manifold w/pex using one full zone of the manifold (no thermostat). Like the idea if the Runtal .... but, the lower outputs and more parts needed always had me going back to the panels.

The panels are like Mini-splits .... once they are up and if done correctly ... the look is fine. Like big radiators in an old house ... most look fine if done correctly.

ewang

On my basement radiators, I've got TRV's on each radiator. This allows me to use a simple tee to branch off to each rad. Fine tuning temperature control to each is accomplished through the TRV adjustment. ECM pump does the rest.

For example, I've got my laundry and guest bedroom rad's tee'd off in the wall. And in my family room where I have two rad's, I just ran one supply and return and just used a normal tee to split between the two.

TAG

Ewang: What type/make of radiator ?

My guess is with the new smart pumps it makes everything a bit easier. When I lived in Germany it was common to see the TRVs used .... even the remote with the very long tube. Both for individual radiators and whole zones of radiant back to the manifold. It was strange to walk into a room and see only the head on the wall ...

I guess using the simple "T" is a factor of cost .... the chrome diverter valves are in the $75 range. They save 1/2 the pex ... but, pex is cheap.

ewang

I used the Pensotti panel radiators. I used their app along with SlantFin heat loss app to get a rough idea of heat loss and everything is working great.