PSI at boiler exceeds 30psi when hot in 4 story house

DIYorBust

Hello, I'm seeking help on a frustrating problem with my hydronic heating system, and I see many folks have gotten help here. Any comments appreciated!

Background: I am heating 4 story 3-family building. We are replacing the fin tube baseboard with steel radiators because the baseboard appeared undersized, and this was confirmed by a mechanical systems engineer, who performed a manual-j, and the radiators are sized accordingly. In the basement is a Navien NHB-150. It was professionally installed by an authorized Navien dealer who is a licensed plumber, and permits were obtained. We have replaced about 1/3 of the baseboard with radiators so far. There is about 40 feet between the boiler and the top floor baseboards. There is an indirect water heater zone, and a single heating zone for the entire building.

Problem: When cold I have the PRV set to fill the boiler to about 22psi. When the system reaches 180 degrees, the pressure at the boiler reaches about 33, and the T&P valve sometimes opens. When the system is pressurized to less than 22 psi or so, the top radiators become airbound and are difficult to purge. This exceeds the specs for the boiler, and I want to address it.

Observations: I noticed that when the pump on the primary loop kicks off, the pressure in the boiler increases to about 28.5 psi even with the system cold. I have a dirtmag below the boiler and the pressure at that point does not increase when the primary pump starts running. It's a grundfos 3 speed pump. I have 2 expansion tanks, an amtrol ex-30, and I added an ex-60 recently to try to address this, both have been charged to 22 psi.

Is this normal? If so what should I do, would a larger expansion tank help? Should the speed of the primary pump be reduced? Please help!

DIY

nicholas bonham-carter

Is the boiler piping correct when compared with the manufacturers installation instructions?
The location of the pump, and expansion tanks is critical.—NBC

SuperTech

The replacement of the fin tube baseboard convectors with the radiators has added a lot more water volume to the system. Have you checked to see if your current expansion tanks are adequate for the water volume? The tanks come with sizing chart, if you don't have it you can check the Amtrol website for it. The circulator motor isn't strong enough to raise boiler pressure on its own, but if the expansion tank and pressure reducing valve are not in the best location its possible for it to be an issue. 

Ideally the circulator should be pumping away from the expansion tank and pressure reducing valve. The expansion tank location is the Point Of No Pressure Change (PONPC) in the hydronic circuit.  With 22 PSI in the system when the circulator kicks on the pressure after it will be slightly higher and the pressure before it slightly lower. If you have the circulator on the return, expansion tank after the circulator and pressure reducing valve before the circulator it's possible that the pressure reducing valve might see low enough pressure to add more water to the boiler.  Depending on what pressure the expansion tank and reducing valve are set for this could lead to the relief valve eventually opening. I like to connect the pressure reducing valve to the PONPC to avoid this scenario. 

EBEBRATT-Ed

We need to see pictures of the piping. You have to run 22psi to reach the 4th floor. 2,31ft/psi=40'/2.31=17.3psi + 4psi margin=22 psi.

This leaves you little room for expansion pressure 8psi

1, the system has to be piped right

2. your going to need a larger than normal expansion tank

3. Check with navien and look to see what pressure the boiler is rated at. Maybe a 40psi relief valve could be installed. DO NOT do this without navien's authorization and only if the boiler is stamped for a higher pressure


4. worse comes to worse you would have to install a heat exchanger and isolate the top floor piping

GroundUp

Sounds like somebody piped it wrong. Can you share a photo?

PC7060

EBEBRATT-Ed said:

2. your going to need a larger than normal expansion tank 

Or you can add a second tank which may be easier than finding room for a larger single tank. 

MikeL_2

Diyor,
Would it be possible to move the boiler to a utility or spare room on the first floor?

DIYorBust

PC7060 said:

EBEBRATT-Ed said:

2. your going to need a larger than normal expansion tank 

Or you can add a second tank which may be easier than finding room for a larger single tank. 

Keep in mind I already have two expansion tanks, I added an ex-60 to the ex-30 the plumber installed, which should increased the volume by something like 175%. I charged both tanks to 22 psi using a bike pump. However it is possible that i need a much larger tank.

DIYorBust

MikeL_2 said:

Diyor,
Would it be possible to move the boiler to a utility or spare room on the first floor?

I did consider this, but it would not be practical at this point given the permits have already been file, the system has been build, the venting is complicated and difficult to reroute through finished space, and there is no suitable location upstairs. It's a connected rowhouse, so the boiler must vent to the roof, wall venting would be a code violation due to the proximity to windows and neighbors.

DIYorBust

GroundUp said:

Sounds like somebody piped it wrong. Can you share a photo?

Note: expansion tanks connect after the sensor well on the lower right. The room is small so it's hard to get a full picture. Pumps are all directed up as far as I can tell. The grundfos 3 speeds are set to max, and the the taco viridien is also at at max speed.

DIYorBust

EBEBRATT-Ed said:

We need to see pictures of the piping. You have to run 22psi to reach the 4th floor. 2,31ft/psi=40'/2.31=17.3psi + 4psi margin=22 psi.

This leaves you little room for expansion pressure 8psi

1, the system has to be piped right

2. your going to need a larger than normal expansion tank

3. Check with navien and look to see what pressure the boiler is rated at. Maybe a 40psi relief valve could be installed. DO NOT do this without navien's authorization and only if the boiler is stamped for a higher pressure


4. worse comes to worse you would have to install a heat exchanger and isolate the top floor piping

Thanks I just added the picture to a previous remark. I agree with the 22 psi recommendation, and empirically that seems to be what is needed to maintain flow in the radiators. The Navien pressure spec is 30 psi max. I can get a large floor mounted expansion tank, but they are not cheap. Do you think that would work? I would say the boiler is reaching 33psi at 180 degrees. So the goal would be to reduce that by about 3 psi. However merely running the primary pump increased the pressy from 22 to 28 at the boiler. It does not increase it significantly outside the primary loop however.

DIYorBust

SuperTech said:

The replacement of the fin tube baseboard convectors with the radiators has added a lot more water volume to the system. Have you checked to see if your current expansion tanks are adequate for the water volume? The tanks come with sizing chart, if you don't have it you can check the Amtrol website for it. The circulator motor isn't strong enough to raise boiler pressure on its own, but if the expansion tank and pressure reducing valve are not in the best location its possible for it to be an issue. 

Ideally the circulator should be pumping away from the expansion tank and pressure reducing valve. The expansion tank location is the Point Of No Pressure Change (PONPC) in the hydronic circuit.  With 22 PSI in the system when the circulator kicks on the pressure after it will be slightly higher and the pressure before it slightly lower. If you have the circulator on the return, expansion tank after the circulator and pressure reducing valve before the circulator it's possible that the pressure reducing valve might see low enough pressure to add more water to the boiler.  Depending on what pressure the expansion tank and reducing valve are set for this could lead to the relief valve eventually opening. I like to connect the pressure reducing valve to the PONPC to avoid this scenario. 

Thanks supertech. Keep in mind it is not the circulator, but the boiler pump that is is causing the pressure at the boiler to hit 28. I believe they are pumping away from the expansion tanks, but check the picture I attached to a previous message. I added an ex-60 to the existing ex-30 more than doubling the expansion tank volume. However I have no simple way to determine the amount of water in the system, the piping predated my presence in the home, but the issue existed and was worse before we changed from a cast iron boiler to a wall mounted boiler.

GroundUp

DIYorBust said:

GroundUp said:

Sounds like somebody piped it wrong. Can you share a photo?

Note: expansion tanks connect after the sensor well on the lower right. The room is small so it's hard to get a full picture. Pumps are all directed up as far as I can tell. The grundfos 3 speeds are set to max, and the the taco viridien is also at at max speed.

In that tee just below the aquastat? There's your problem. With that much tank volume, the pressure should never change regardless of water temp. The fact that it's changing by merely spinning the boiler circ says that the boiler circ is pumping right at the PONPC. If the connection is in fact that tee below the aquastat, that is absolutely the case.

DIYorBust

I kind of

GroundUp said:

DIYorBust said:

GroundUp said:

Sounds like somebody piped it wrong. Can you share a photo?

Note: expansion tanks connect after the sensor well on the lower right. The room is small so it's hard to get a full picture. Pumps are all directed up as far as I can tell. The grundfos 3 speeds are set to max, and the the taco viridien is also at at max speed.

In that tee just below the aquastat? There's your problem. With that much tank volume, the pressure should never change regardless of water temp. The fact that it's changing by merely spinning the boiler circ says that the boiler circ is pumping right at the PONPC. If the connection is in fact that tee below the aquastat, that is absolutely the case.

The pump pumps into the boiler, and then down the bottom of the primary loop. I kind of see what you're saying but if that's the case, where can I connect the tanks so that they do not experience positive pressure when the boiler circ runs?

EBEBRATT-Ed

@DIYorBust

I cant tell which way it's pumping but you need to have the expansion tanks on the suction side of the pumps.

If you have to have 22 psi cold its questionable if you can stay low enough to keep the relief valve from blowing unless you put an heat exchanger in for the top floor or for the whole building. That't would probably be the best way out

DIYorBust

Tank connection picture.

DIYorBust

DIYorBust

I did an experiment just now. With the boiler temperature at 178 and the boiler pressure at 31.9, I turned off the thermostat. When the pump shutoff the boiler pressure dropped immediately to 26.1 with the temp unchanged. I didn't wait for the water to cool to room temp, but the prv is set to about 22 psi. So I wonder, is it possible the boiler loop pump is too large, or the primary loop piping is too small?

DIYorBust

EBEBRATT-Ed said:

@DIYorBust I cant tell which way it's pumping but you need to have the expansion tanks on the suction side of the pumps. If you have to have 22 psi cold its questionable if you can stay low enough to keep the relief valve from blowing unless you put an heat exchanger in for the top floor or for the whole building. That't would probably be the best way out

A heat exchanger would solve the pressure issue, but it seems like that would considerably reduce the efficiency and responsiveness of the system. The heating has only 1 zone for the building, and it would not be easy to repipe the top floor to a different zone. The condensing boiler. would probably have to run always at 180. It seems like it might be a better solution to pipe the relief valve down close to the floor drain and let it do it's thing, but something doesn't feel right about doing that.

DIYorBust

As I'm learning more, I see something that might be unusual here. The circulators take from one side of the primary loop and return to the other. There is no way for water to circulate through the emitters without being pumped at least partly through the boiler. Usually the circulators would return very close to where they take off the primary loop. However would changing this actually reduce my pressure by 2-3 psi? Would reversing the direction of the secondary pumps help?

GroundUp

Are you using the digital Navien pressure gauge? They always read high when the circ is running, poor sensor placement IMO. I see now that the tank connection is not where I'd originally thought, where you have it is certainly better. Others will disagree with me on this and we had a debate just the other day, but I've monkeyed around with this enough to say with 100% accuracy that the tank should be connected in the flow stream- in your case, maybe under the air eliminator where the factory expansion tank connection point is located. I have run across this many times where the tank is connected off to one side like this, and relocating the connection point to the flow stream (along with air pressure correction) solves the issue every time. While I don't know the science behind it, I know that it has worked for me upward of a dozen times in the field. When you say that you charged the tanks to 22 psi, did you do that while there was zero pressure on the water side? What type of gauge did you use?

hot_rod

I think you have this piping? Or an attempt at it?
if so the expansion connection would be best at the return end, as your boiler/ primary pump could be pumping at the tank now. Theoretically

Be good to know exactly your elevation from where the tank connects to the highest point. You may get away with 20 psi fill pressure. measure the actual distance, or put a gauge at the highest point.

EBEBRATT-Ed

Then just put a heat exchanger on the whole system. I just don't think your going to get a 40' high system to work with a 30 psi relief valve.

Wishing it would will not make it happen you can't change the laws of nature. All expansion tanks are sizeon some sort of pressure rise. You can add any # of tanks that you want.

How close to the 30# relief valve do you think you can run reliably without having it drip? I would think 25 is about the limit. You need 22 psi without any allowance for expansion. Do you think you can keep the expansion under 3 psi?

bburd

The only alternative IMO would be to change the boiler to one with a higher pressure rating that can safely take a higher pressure relief valve.

I lived in a six story converted townhouse in Boston that had hot water heat with a 60 psi boiler and relief valve. 50 psi is not uncommon.

MikeL_2

Why have a modulating / condensing boiler if you need to run at high temps? 
  Can your emitters meet the design space heating required with a swt at or below 135°? If not, use some type of supplemental heating during extreme cold weather.
   Your boiler may be able to operate with constant circulation & outdoor reset with a max swt of 135°.

DIYorBust

GroundUp said:

Are you using the digital Navien pressure gauge? They always read high when the circ is running, poor sensor placement IMO. I see now that the tank connection is not where I'd originally thought, where you have it is certainly better. Others will disagree with me on this and we had a debate just the other day, but I've monkeyed around with this enough to say with 100% accuracy that the tank should be connected in the flow stream- in your case, maybe under the air eliminator where the factory expansion tank connection point is located. I have run across this many times where the tank is connected off to one side like this, and relocating the connection point to the flow stream (along with air pressure correction) solves the issue every time. While I don't know the science behind it, I know that it has worked for me upward of a dozen times in the field. When you say that you charged the tanks to 22 psi, did you do that while there was zero pressure on the water side? What type of gauge did you use?

Ok yes I'm referring to the digital gauge on the boiler, but I also have a regular gauge on the dirtmag a little below the boiler. I replaced my gauge, I think it was a watts with another gauge initially when it didn't match the boiler, but I see now it does match the boiler when the pump is not running. Are you saying I should connect the tank to the primary loop manifold? Or just somewhere before the zone pumps?

When I say the tanks were charged to 22 psi, I performed this check on the larger tank before installing it using a bike pump with a built in gauge. I charged the smaller tank with the system drained down. I agree the navien digital pressure sensor is suspect. The T&P valve never blows until the pressure reaches about 34 on the digital readout, but it could be higher inside the boiler. Is it a practical goal to keep the pressure from rising from 22 psi to 30?

DIYorBust

hot_rod said:

I think you have this piping? Or an attempt at it?
if so the expansion connection would be best at the return end, as your boiler/ primary pump could be pumping at the tank now. Theoretically

Be good to know exactly your elevation from where the tank connects to the highest point. You may get away with 20 psi fill pressure. measure the actual distance, or put a gauge at the highest point.

From the boiler to the highest point is approximately 40 feet, it might be a little less I suppose. 21 psi cold might be enough but 19-20 area seems to give me trouble with air at the top. It might be possible to turn it down to 21 once it's been running for a few weeks and most of the air is out of the system. It's a bit difficult to pinpoint the exact minimum needed. There's no connection point for a gauge at the top of the piping currently.

DIYorBust

MikeL_2 said:

Why have a modulating / condensing boiler if you need to run at high temps? 
  Can your emitters meet the design space heating required with a swt at or below 135°? If not, use some type of supplemental heating during extreme cold weather.
   Your boiler may be able to operate with constant circulation & outdoor reset with a max swt of 135°.

Well the indirect won't work very well at 135 degrees for one thing. One reason I'm installing the radiators is that I want to run on outdoor reset and the baseboard is not big enough to turn down the water temp.

DIYorBust

bburd said:

The only alternative IMO would be to change the boiler to one with a higher pressure rating that can safely take a higher pressure relief valve.

I lived in a six story converted townhouse in Boston that had hot water heat with a 60 psi boiler and relief valve. 50 psi is not uncommon.

Yes there are some 50 PSI units. But is it really unsafe to to run at 32 psi and wait for the boiler to leak before I buy a new boiler?

DIYorBust

EBEBRATT-Ed said:

Then just put a heat exchanger on the whole system. I just don't think your going to get a 40' high system to work with a 30 psi relief valve.

Wishing it would will not make it happen you can't change the laws of nature. All expansion tanks are sizeon some sort of pressure rise. You can add any # of tanks that you want.

How close to the 30# relief valve do you think you can run reliably without having it drip? I would think 25 is about the limit. You need 22 psi without any allowance for expansion. Do you think you can keep the expansion under 3 psi?

I'm not sure, it sounds like you're saying the answer is no, but I would like to try if it is possible. Would a giant 44 gallon expansion tank possibly do the job?

DIYorBust

So looking at this calculator:
http://tools.watts.com/ETNP/
It looks like I may be able to keep the expansion under 3 psi assuming i have say a 30-40 gallon system with the radiators, and I use a 60-80 gallon expansion tank. I'm not sure how accurate any of those assumptions are though, or what margin of error the calculator uses.

hot_rod

Trying to visualize how you get 40' above the expansion tank?
Call the basement 3' since the tank is up high. 9' per floor assuming 8' walls 12" joists. the rads on the 4th floor near the floor? I come up with about 32' X .433= 13.8 psi, add 2 psi positive. 18 psi should be plenty.

Even if it is 40' X .433= 17 +2= 19 psi. call it 20, gives you at least 8 psi buffer before relief.

A 30 lb relief should go pretty close to 28- 30 before seeping?

Wessel and Amtrol have expansion tank sizer. Use the commercial sizer as it allows you to enter gallon of system capacity. Guesstimate the volume. You may be a buit shy on tank, if in fact you think you have 150 gallons?

Here is a Wessel calc ,150 gallons up to 180F

DIYorBust

Thanks hotrod, the expansion tank is near the floor, however it's the boiler that appears to be the one component that would be sensitive to the pressure and that is on the wall. The building is about 40 feet tall with the tank in the cellar. It could be closer to a 36 foot difference or so with the boiler being on the wall, it is somewhat difficult to measure with the ground floor being partly below grade, but I see your point here. I might be able to get away with 20 or 21 psi. However when I run below 20 I can tell you I get air in the top. It does seem like it would be useful to connect a gauge to the vent tee on the top floor baseboard, I'll have to get an adapter.

I think it's unlikely I have 150 gallons, the riser piping runs I'm guessing very roughly  might be 250 feet of 1.25 inch, plus the radiators and some branch piping seems like maybe 30?

Edit: it occurs to me the top floor is only 7 feet tall so the radiator may be a foot or two higher than if the floors were the same size.

EBEBRATT-Ed

@DIYorBust
you know you need 21psi because you have problems when you are blow that, so that is a given. It's unlikely you can put an expansion tank in large enough to keep your pressure rise when heated below 28 psi. That only gives you 6psi maybe because relief valve are not control devices they are just a spring loaded valve and not that accurate.

I knw you don't want to go for a heat exchanger but what are you going to do when you go to the expence of a larger expansion tank and it doesn't work?

Heat exchangers are fairly cheap, you already have the expansion tanks so you need a little piping and another air removal device and your in business

MikeL_2

Diyor, 
      I think you understand my suggesting lower swt. Is it possible to increase your dhw storage capacity so a max swt of 140 - 160 will meet the demand during peak draw?

hot_rod

EBEBRATT-Ed said:

@DIYorBust
you know you need 21psi because you have problems when you are blow that, so that is a given. It's unlikely you can put an expansion tank in large enough to keep your pressure rise when heated below 28 psi. That only gives you 6psi maybe because relief valve are not control devices they are just a spring loaded valve and not that accurate.

I knw you don't want to go for a heat exchanger but what are you going to do when you go to the expence of a larger expansion tank and it doesn't work?

Heat exchangers are fairly cheap, you already have the expansion tanks so you need a little piping and another air removal device and your in business

At 30 gallons of system volume a #60 is adequate, at 50 gallons you need a larger tank.

The B&G #790 is the relief valve of my choice. It's working area is about 5 times larger than the small pricepoint valves. More accurate and all brass.

ideally, once a relief valve has gone off, it is wise to replace it.

GroundUp

With both a #30 and a #60 properly charged and connected, you should easily have enough capacity to bring 100 gallons of fluid from 60 to 180 degrees without the pressure changing at all. I sincerely doubt that you have that much volume, which eludes to either an improper air charge or an improper connection. Like I'd said earlier, others will disagree, but if it were mine, I would relocate the connection point to the bottom of the air eliminator where it's designed to be and reduce the air pressure in both tanks. Low pressure gauges can be pretty funky, so even though your gauge said 22, I suspect it's actually higher than that which is not allowing as much acceptance as it should be. Every time I run into this problem, it's solved by performing the aforementioned rework. I can't say positively from here that it will solve your problem, but so far it's 100% effective for me. Others will also disagree that pressure shouldn't fluctuate, but the whole function of the expansion tank is to maintain a given pressure. If it's fluctuating at all, there's room for improvement. Personally I have approximately 95 gallons in my entire system at home and the pressure stays 15 psi whether it's 60 degrees or 160 degrees, using two #30s

DIYorBust

GroundUp said:

With both a #30 and a #60 properly charged and connected, you should easily have enough capacity to bring 100 gallons of fluid from 60 to 180 degrees without the pressure changing at all. I sincerely doubt that you have that much volume, which eludes to either an improper air charge or an improper connection. Like I'd said earlier, others will disagree, but if it were mine, I would relocate the connection point to the bottom of the air eliminator where it's designed to be and reduce the air pressure in both tanks. Low pressure gauges can be pretty funky, so even though your gauge said 22, I suspect it's actually higher than that which is not allowing as much acceptance as it should be. Every time I run into this problem, it's solved by performing the aforementioned rework. I can't say positively from here that it will solve your problem, but so far it's 100% effective for me. Others will also disagree that pressure shouldn't fluctuate, but the whole function of the expansion tank is to maintain a given pressure. If it's fluctuating at all, there's room for improvement. Personally I have approximately 95 gallons in my entire system at home and the pressure stays 15 psi whether it's 60 degrees or 160 degrees, using two #30s

Well it seems worth a try, is it a half inch npt on the air valve usually?

hot_rod

DIYorBust said:

GroundUp said:

With both a #30 and a #60 properly charged and connected, you should easily have enough capacity to bring 100 gallons of fluid from 60 to 180 degrees without the pressure changing at all. I sincerely doubt that you have that much volume, which eludes to either an improper air charge or an improper connection. Like I'd said earlier, others will disagree, but if it were mine, I would relocate the connection point to the bottom of the air eliminator where it's designed to be and reduce the air pressure in both tanks. Low pressure gauges can be pretty funky, so even though your gauge said 22, I suspect it's actually higher than that which is not allowing as much acceptance as it should be. Every time I run into this problem, it's solved by performing the aforementioned rework. I can't say positively from here that it will solve your problem, but so far it's 100% effective for me. Others will also disagree that pressure shouldn't fluctuate, but the whole function of the expansion tank is to maintain a given pressure. If it's fluctuating at all, there's room for improvement. Personally I have approximately 95 gallons in my entire system at home and the pressure stays 15 psi whether it's 60 degrees or 160 degrees, using two #30s

Well it seems worth a try, is it a half inch npt on the air valve usually?


Assuming your air sep to pump relationship is ideal

In you system the better air sep location would be the supply line out of the boiler, a vertical mount sep. The boiler supply outlet is always the hottest point. Once you move it to the loop downstream of the closely spaced tees, it sees a blended temperature.
Still works okay, but not the very best location, techically speaking.


In your case connecting the tanks to the port on top of the Dirtcal would in fact have all pumps, including the boiler pump "pumping away" Since it looks like the pump on the boiler is pumping up into the boiler, on the return side, hence pumping at the PONPC.

I doubt moving it from where it is, 12" or so to the left, where the air sep is will change anything.

psb75

I'm not so sure that having a pressure gauge at the bottom of a DIRT SEPARATOR is the best place to get an accurate system pressure reading. Where is the "air" that you say collects in the upper radiators coming from? Your system should be closed to air. Once it is removed, it should not reoccur--regardless of system pressure.

psb75

I don't see any fill-valve and back flow preventer. Where might that be ? And what might the fill pressure be set at? It usually comes "off the shelf" factory-set at around 12-14 psi. Do you perhaps have that fill pressure "boosted" too much?