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

EdTheHeaterMan

This might be too easy of a fix ( if the 50# relief valve is not an option) but I recall working on boilers on the top floor of a 12 story hotel building.  The standard 30# relief valve was no problem.  The static pressure up at the top of the 12 story building was less than 8psi.  

Could you find a utility closet on the second or third floor to install the boiler and expansion tanks?  Then run some 1-1/2” mains from the system current location to the new higher location?  

I like to think outside the box, or in this case … outside the boiler room!

archibald tuttle

@neilc "A thermal expansion tank needs the air pressure set to match the cold fill pressure or elevation delta of the house or building system."

I would say it needs to have the air pressure set distinctly (vs. greatly) above the cold fill pressure. I often do this by observation rather than gauges if I'm shaving it close insofar as operating and blow off pressure.

Jamie Hall

Oh my. Well, several comments. Listen to @hot_rod on expansion tanks. He's right, of course. Second, the physics of an expansion tank on a heating system is exactly the same as that on a well tank — just the pressures are different. Third, whoever said that anything rated over 30 psi has to be ASME approved for the pressure. Fourth, the labelled safe operating pressure of a system — such as a boiler — may not be more than half the test pressure. Thus something rated at 30 psi must be able to withstand 60 psi under test. That is called, for some odd reason, a "safety factor". Fifth, if you put a pressure relief valve rated at some higher pressure — I see someone up there mentioned a 40 psi valve on a 30 psi boiler — you have just cancelled all of your insurance and any equipment warranties you might have had.

Now. Without reading the whole thread, I take it we have a four story building here? Let's assume that the highest emitter then is 32 feet above the boiler and it's pressure gauge. That means there will be a 14 psi difference in the static system pressure from the top to the bottom of the system. That also means that there is absolutely no excuse, assuming the expansion tank is working and sized right, for the static pressure at the boiler to exceed 20 psi cold and 25 psi hot. If it does, something's wrong.

And so, don't argue about it. Fix it.

archibald tuttle

@DIYorBust just noticed the bit about the indirect water heater.

<Nevertheless, lowering the temperature is not ideal with an indirect water heater zone. I keep the water in the tank close to 180 and mix it down. The loss of recovery time and storage capacity would make the hot water supply inadequate if I turned it down much unless I upsize the indirect.>

lowering the temp to the rads doesn't usually lower the temp delivered to an indirect if it is a relay that knows it is for an indirect. If it has priority function it won't heat the whole system to those temps so it shouldn't be the challenge/weak link for system pressure although all the pics are of the manifold and piping below the boiler and i can't see how it is vented. stack temps can get inappropriately high from those 180 degree supply to indirect DHW for many plastic vents. I know late models are monitoring stack temp and modulating to protect against this but that doesn't heat water very well. so when you are thinking about the overall solution, I use a flo-style on-demand heater anywhere that I have sufficient gas supply. (I suppose you could get a relay and create your own priority system that would shut off or mod down the boiler while the hot water heater is calling, a little clunky but definitely DIYorBust. After all, with a priority system for the indirect that is what is happening anyway.

I had should season problems when I had an indirect. If I enable priority then fan coils would go cold while folks were taking showers. but if I didn't then the hot water making temps circulated in the system and overheated the rooms.

I really like separating these appliances.

No question it is nice if you can run the pressure 20-25 on a four story. I have definitely worked toward that and use mutliple small or a large expansion tank setting the static cold air pressure to like 21 to 22.

PRR

Without reading the whole thread

Thread was over in 2022. OP has not been back. (I don't know if the problem was resolved.)

archibald tuttle

@PRR funny, it just started up again. i didn't remember how long ago the original had been. it just popped up in my email because I had commented, but i'm fascinated by pressure balancing between good circulation and boiler operating limits. I admit I push the limits (not by raising the relief above the requisite limit, but by running up to it in tall(ish), i.e. 4 story buildings. never had a 5 story to contend with.

First low mass boilers I bought were the heatmaker direct hot water makers (these were not flow heaters generally, they didn't trigger on flow anyway; they were more like the typical heatmaker boilers but they they had a 150 psi pressure rating (although the internal unions leaked under 40 lbs. when they came from the factory. had to do some fancy wrench work to reach amongst the workings and tighten them up.

I put 45 lbs reliefs on them and that was way plenty so I wasn't anywhere near the pressure limit. I liked them alot. Although they shipped at 250 M and specified ABS or CPVC for vent but that was too hot exhaust at high temps and I couldn't get return temps down enough to get much condensation especially because they didn't modulate. So I replaced near boiler iwth CPVC and downfired to 175 M and was happy but after 20 years the writing was on the was on the wall and ultimately replaced them with 140M munchkins so i had to cut back to 30 psi.

But since i'm pumping away I had the system cold pressure still up in the mid 20s and, on the pressure side of the system pumps (primary secondary) I would exceed 30 lbs. system hot but the returns were upper 20s with system loss. (it was always pumping, i ran it constant circ with deep setback, the modulation is perfect for that, and took the DHW load off onto a flow heater. Been really happy with this settup. As long as I can get the munchkin parts, which I keep essentially a whole boiler's worth on the shelf, I'll never change. heat exchangers, so far so good. the pressure was delicate balance because i was close to the "relief range" of tripping but as long as the PRV was on its game everything was perfect and I almost never had air in the fan coils on the top floor.

DIYorBust

https://forum.heatinghelp.com/discussion/comment/1807366#Comment_1807366

The OP does check this thread from time to time and thanks everyone for their comments! At any rate, I did not yet find a satisfactory solution. But we have managed it in a number of ways. One thing that has helped a lot was installing automatic air vents on the top floor. Worried about leaks I did choose a caleffi minical valve that has a hygroscopic disc designed to close the valve if the float fails. It's not an ideal solution because I do not think it is a good practice to allow air into the system because I understand it leads to corrosion of the components. Therefore we've still been making adjustments and trying to keep the pressure in range. I haven't installed the radiators up on the top floor yet because I don't want to make the problem worse. While I'd still like a better resolution, the Navien has now been about 8 years in service. The last Navien tech who serviced it for an issue other than the pressure problem, suggested replacing it rather than servicing it. Now I had hoped it would last 10-15 years. I selected this boiler because I thought that having a common boiler would make it easier to find parts and technicians. But lately it has not been easy to find technicians to help, and I still find myself stocking parts, because my experience was supply houses are hit or miss, charge extra when I need parts quick, and most aren't open on weekends, holidays or after hours. So I'm starting to think about moving up the replacement cycle a bit here.

After reviewing this thread, and checking the submittal, I notice that triangle tube makes a boiler that is rated for 50psi. The lochinvar knight looked promising, but the ones I looked at were 30 psi rated. Are there any other boilers folks here like that I could consider? Obviously looking for a version that has a pressure rating larger than 30psi.

Thanks!

DIY

GGross

https://forum.heatinghelp.com/discussion/comment/1831646#Comment_1831646

Viessmann B1HE-150 and B1hE-199 are both rated for 60 PSI max working pressure, their smaller ones are 45, they all come with 30PSI relief valves which is standard so you would need to source a new relief valve. I would think it might be a simpler fix to just properly calculate a new expansion tank size at this point? A huge expansion tank seems like it would be less money than a new boiler.

DIYorBust

We've installed a #60 and a #30 tank. I could buy a 20 gallon tank. It's difficult to estimate the total volume in the system. We have installed 5 steel column radiators. Using the bell and gosset guide discussed in another post here, it seems we should have adequate capacity, but honestly I'm not really sure. I haven't seen a sudden pressure jump, and the pressure drops when the pump turns off. I haven't really had a great experience with this boiler. Navien only supports it's own authorized techs to work on the boiler, and it hasn't always been easy to get one when there's a problem. I haven't found it to be as reliable as I'd like either. Maybe it wasn't installed as well as it could have been, or maybe I just got unlucky, but it's 8 years old. If it bites the dust sometime in the next couple years, I may have to replace it with whatever and whoever I can find under the gun. Pay a couple hundred here and there for service calls, and cross my fingers whenever I'm out of town. Is it worth trying to limp along a couple more years? If we do replace, it might make sense to put in a larger expansion tank anyway. The house has a total heating capacity on the manual-j of around 85kbtu. If we oversize the radiators a little bit, it might make sense to put in a larger expansion tank anyway How big a tank or tanks do you think would be enough not to worry? 20 gallons? I didn't see a consensus here on whether a large tank could be expected to provide the level of precision we need. Some comments suggest that the pressure should not move at all with a large enough tank, but others said it would not be feasible to keep the pressure in such a tight range. It does seem like a 50psi boiler would allow us to install a 50psi relief valve, and keep the system filled. I don't love it, but I'm pulling my hair out here. Do you think the navien is likely to hold up another 5 years?

hot_rod

As long as water expands when heated, the pressure will increase.

It is sometimes easier to add #30 tanks instead of a large ASME certified larger tank.

Or look at a full acceptance style tank. At least price the option. Horizontal mounting doesn't frighten them either :)

Wessel and Zilmet have full acceptance tanks available.

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