Cast iron system not heating well
Ive inherited a home that has been known for decades to not heat well. I would greatly appreciate if y'all could help me figure out what the problem is.
2,500 sq ft house. 600 EDR of cast iron radiators. 111k heating combi boiler. The system as a whole does not flow well. The last radiators have problems freezing even with all the others throttled down.
When i open the "valve" all the way near the boiler, the heating water short circuits into the boiler
return and never makes it into the system. The system only heats when the valve is closed and all water is routed through the boiler. It being a combi, this creates a big flow issue. I have included a diagram. Can anyone point me in the right direction? Thank you. -Jon
Comments
-
is it a conventional combi such as is somewhat common in europe vs a condensing boiler?
does the boiler have a built in circulator?
0 -
might be best to have primary secondary or a hydraulic sep.If it is a combi, it has a pump inside.
But it may not have the capacity to flow the boiler and distribution piping.
The boiler manual should have some piping info.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
2 -
It is a noritz nrcb199dv. It has a built in circulator as well as a seperate circulator in the system piping. This problem has existed years before this boiler was installed. It is piped primary secondary, but will not heat unless the bypass valve is closed. Effectively making it no longer primary/secondary.
0 -
You need to make the system "primary secondary" to make it work.
The boiler loop has to flow enough water to keep the boiler happy.
The heating loop need to have enough flow to satisfy the radiation. You may need balancing valve on the radiation loops if you don't have them.
You need to have 2 circulators if you only have 1 you will have issues
too bad that the radiation furthest from the boiler is 1/2" which will make it more difficult to balence but it may be ok if sized properly.
Combis and condensing boilers have a large pressure drop.
need more info on the # of pumps and pictures of the boiler piping.
0 -
where are the radiators physically located? are they on multiple floors or all one level? are the ones shown above and below in your diagram physically above and below? is the return piping above? it may be very difficult to get enough flow to purge the system and you may need bleeders on the piping if the radiators aren't the high point. if you do purge you probably need to open only one pair of radiators at a time.
0 -
you probably need around 10gpm through the boiler to move the output of the boiler. yo may need more in the system to make it even although if parts are actually freezing it is probably air bound or has broken valves or something like that.
0 -
but what you have is not primary secondary. you have 2 circulators fighting with each other and a valve trying to play referee.
0 -
The radiators are physically above one another on two different floors. The piping in the attic is sloped upward with the highest point having a bleeder vent. I should have put that on the diagram. It shouldn't be air bound. The way it is piped, almost everything is self bleeding.
I am not sure if it is piped or pumped correctly, as it has had many attempts to make it heat better.
0 -
you also might not have enough circulator for that system. many people just use a taco 007 and it usually is close enough but you might need more flow.
the valves may not be fully off when they are off, many valve have a tiny bypass built in to keep the radiator from freezing when the valve is off. if you don't have enough circulator that could be enough to keep the far radiators from heating.
having the radiators stacked on 2 different floors poses a balancing problem because the load on the 2 different floors won't be the same but obviously you are controlling flow in both when you try to balance. ideally they would have selected radiator sizes to keep them more or less balanced.
0 -
This piping topology looks like a remnant from a non-condensing cast iron boiler system.
I would not consider that as closely spaced Tees.
Does the boiler short cycle ?
Internal circulator running when expected ?
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System
1 -
What you have is not primary/secondary, although it's not always necessary if the onboard circ can provide adequate flow to cover the load.
It sounds like you've tried balancing flow, but to clarify, if you close off every radiator besides the ones in question are they still cool? There is obviously a flow problem somewhere, but narrowing that down will require some diagnostics. Assuming the circ is adequately sized, there may be a blockage in the piping or rad(s) somewhere. While uncommon, I have seen a few times where sludge builds up in the base of the rads and inhibits flow. Several times I've found debris in the piping (usually against an elbow or valve) that was accidentally left in there during construction. Once upon a time, I found the metal end cap of a fitting brush wedged in the cup of a fitting that must have broken off of the brush during cleaning prior to installation.
0 -
The only thing i am certain about is all the air being purged. Boiler, radiators, piping. And the radiators being balanced. Ive calculated EDR, and they are all about right for the room they are in. All the radiators are throttled down with the furthest from the boiler being wide open.
I have included a new diagram more true to how it is set up in real life.
With the "bypass" valve open, the boiler short cycles immediately. The supply water goes directly back into the boiler, it thinks the system is hot and the burner turns down.
With The bypass valve closed, it forces all water through the boiler and it heats properly, but causes a flow issue as the boiler can only move so many GPM.
0 -
if the boiler short cycles when the bypass is open either the system pump isn't moving much water on its own or the boiler circulator isn't working. though it isn't really quite p/s it should act more or less that way with the bypass open. probably the first thing to do is to do the math on the external circulator. also make sure the controls are set up right to run the external circulator on a dh call however that is set up.
some pictures of exactly what is there would help too because the sketch is simplified and may be missing something important.
what kind of emitters are these? are they standing cast iron radiators or are they something more restrictive?
0 -
You have to go back to the basics.
You know the EDR, so you know the btu output of the radiators. Since you know the total radiation load you divide that # (600edr x 150)= 90,000/10000=9gpm. I would go slightly larger like 10-11 gpm. this is for the heating loop.
Change the piping to primary secondary
Then the secondary pump need to move 10 gpm against the resistance of the piping and the radiators.
So you need to calculate the pip resistance.
The simplified method (which I don't like) is to take the longest run of pipe from the boiler to the radiation and back to the boiler and find the pipe length of the total run and look up the resistance to flow. We can help with that.
Then you size the pump at 10gpm @ X# of feet of head (which you get from the calculation)
0 -
there are likely multiple problems now.
i don't like the opening the bypass makes the boiler unable to distribute its heat energy. either one of the 2 circulators sn't running or is air bound or if the resistance of the system is great it takes a combination of the head of both circulators to move enough water. that is unlikely unless the emitters are very restrictive.
but that isn't the original problem i don't think, it is a problem created trying to fix the initial problem
0 -
I think the issue is your system pump is not working. When you close the bypass, you are now using the boiler pump to push through the system that is why you get heat.
If that bypass is big enough (~1 1/4" ball valve), it can work as a PS loop. Not ideal, but not enough to re-plumb the whole setup.
With a working and correctly sized secondary pump, you should get proper heat with the bypass fully open.
0 -
If you are going to go to the trouble of re-piping the closely spaced Tees do it like the manual shows, not like your sketch.
National - U.S. Gas Boiler 45+ Years Old
Steam 300 SQ. FT. - EDR 347
One Pipe System0 -
You do not have a primary secondary piping unless there is a header inside the boiler. Their piping diagram seems to indicate that the installer provides the separation.
Closely spaced tees is the simplest way. I prefer a hydraulic separator to accomplish 4 things
here are two options.
You want the air purger on the hot side of the system, not return.
Do the radiators have hand wheel valves to balance each one?
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0
Categories
- All Categories
- 87.7K THE MAIN WALL
- 3.3K A-C, Heat Pumps & Refrigeration
- 59 Biomass
- 430 Carbon Monoxide Awareness
- 129 Chimneys & Flues
- 2.2K Domestic Hot Water
- 5.9K Gas Heating
- 122 Geothermal
- 170 Indoor-Air Quality
- 3.8K Oil Heating
- 79 Pipe Deterioration
- 1.1K Plumbing
- 6.6K Radiant Heating
- 396 Solar
- 16K Strictly Steam
- 3.5K Thermostats and Controls
- 56 Water Quality
- 51 Industry Classes
- 51 Job Opportunities
- 17 Recall Announcements