Newly roughed in radiators not warming up

PlumbBob2075

NG fired steam boiler converted to water

2 sets 2” copper supplies and returns for risers then horizontal mains are 2” black iron 

No circulator or zones, 1 thermostat 1st floor(basement, 1st, 2nd, office in attic)

customer wanted to install new bottom piped rad on 2f addition and relocate previously installed bottom piped rad on 2f addition(back to back rooms)

one rad on 2f gets warm, hot at supply valve, but only warm rad. Newly installed rad remains cold. All lines were pressure tested and rads have been pressure tested

need help here boys! All other rads including attic get hot hot hot. Addition rads not working properly 

Jamie Hall

I hope there are bleeders at the top of the new radiators, and that they have been thoroughly purged.

Alan (California Radiant) Forbes

Might be an air problem. Have all the radiators been bled and all the pipes been purged of air?

Ironman

“No circulator or zones, 1 thermostat 1st floor(basement, 1st, 2nd, office in attic)” 

Are you trying to achieve flow by gravity?

PlumbBob2075

They all have bleeders and were purged of air, supply and return fittings all new from supply house, is acting as a gravity fed system. My 2 problem children both have 3/4 lines(S&R) for each, piped in 3/4 HePex, but are tied together respectively to a branch off the 2” black iron main. 

bburd

The Dead Men had piping practices for gravity hot water heat that have fallen out of use since most new systems have used forced circulation since the 1930s. Dan Holohan’s book “How Come?” goes into detail about these. Pipes were larger than those needed for forced circulation.

Installing a correctly sized circulator might be the easiest way to solve your problem.

EBEBRATT-Ed

@PlumbBob2075

Confused. If you converted a steam system to gravity hot water and don't have a circulator that's an issue

If your trying to heat radiators with 3/4" pipe on gravity that probably won't work without a pump

PlumbBob2075

PlumbBob2075

EBEBRATT-Ed said:

@PlumbBob2075 Confused. If you converted a steam system to gravity hot water and don't have a circulator that's an issue If your trying to heat radiators with 3/4" pipe on gravity that probably won't work without a pump

We did not convert, unit has been converted by an outside contractor. I’m green when it comes to gravity fed systems. I’m in the process of reading Dan Holohan’s Classic Hydronics. Helping, but need answers sooner 

EBEBRATT-Ed

@PlumbBob2075

I fear the pex will not be large enough to heat the rads without converting to forced hot water with a pump.

Also, the unavoidable ups and downs of the pex loops will make air removal very difficult when operating gravity


I think (and I am making some assumptions) if the "original house" was and remains gravity and worked in the past then make the new rads on the pex system a different zone with a pump.

What I would be concerned with is the pump flow disrupting the "original" gravity flow. This could be solved with a small brazed plate heat exchanger.

I doubt your going to have any luck making the pex system work on gravity

We will see what others that know more than i have to say

STEAM DOCTOR

Never going to work without a circulator. You will probably need to separate into different zones. Zones with the smaller pex will need to be separated from zones with larger pipes. You will have flow issues otherwise. Proper piping by the boiler might be helpful. Separation of some sort is the key.

Ironman

Not only do you need a circulator(s), but I don’t see an expansion tank. Is there one?

Alan (California Radiant) Forbes

There's a plain steel x-tank shown in a couple of the pictures.

@EBEBRATT-Ed said:

I think (and I am making some assumptions) if the "original house" was and remains gravity and worked in the past then make the new rads on the pex system a different zone with a pump.

I agree.

JUGHNE

The gravity systems I have encountered have large horizontal piping, one has 2 x 4" main take offs of the boiler. The returns were 2 x 3" dropping to the bottom of the boiler. Supply sloped up away from the boiler and return sloped the same....as if they were drain lines that emptied into the boiler.

The first floor rads were fed with 1" to 1 1/4" run outs.
All take offs (first & second floor) came of the top of the main or at a 45.

Now the second floor rads had only 3/4" risers, they were exposed on the first floor so are easy to follow. One set of 3/4" risers even feeds 2 rads back to back.
All of these work very well.

The main feature is that the 3/4" riser goes straight up for maybe 10'.
I believe the smaller pipe works well because of the vertical rise which induces gravity flow. In the basement the 3/4" may be connected to a 1" horizontal run out off the main.

If your pex had the vertical rise of the full first floor then you may get the flow needed. The horizontal with some wavy runs may not be friendly to gravity floor.
Maybe you could you try a solid pipe over sized horizonal run out in the basement, if you had a somewhat straight up shot to the rad. Just a WAG.

Did you check for restrictive orifices in the supply valves?

Steamhead

I agree- that PEX will never work.

Unless you're willing to convert the entire system to forced circulation, you need to repipe these rads in copper, using the same size pipe as similar-sized radiators in that system.