Vacuum relief valve on hot water storage tank

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burto17rn

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I am a DIY home owner in Michigan under the 2015 IPC. I sent my inspector a "How does this look?" picture via email. He responded that the hot water storage tank needs a vacuum relief valve. The code he is referring is "P2804.7 Vacuum-relief valve" and is referenced below. I attached a picture of my combi-boiler setup to this post along with a sketch of my plumbing. The hot water storage tank is on the domestic (potable) hot water side of my combi-boiler, so you can ignore the "boiler" part. This is strictly a hot water question. I have done a lot of research on how vacuum relief valves should be installed. My understanding is they should be on the cold water inlet at least six inches above the tank. Well, its not that simple with my setup here. My hot-water storage tank is setup so that it only receives and discharges hot water. It recirculates water back to the water heater when it drops below a set point via an aqua stat and a stainless recirculation pump. I did it intentionally this way because I don't want hot and cold mixing in the tank. In theory I may see a pressure drop at the fixtures with a prolonged high demand, but never a temperature drop. So this the question is... where do I put the vacuum relief valve? Seems to make the most sense to put it right up on top, but that puts it on the hot side. If I put it how I proposed on the cold side above expansion tank then the vacuum relief valve is before the combi-boiler. That option seems odd as well. I could put it on the "inlet" side of the storage tank, but that water is also hot. The WATTS LFN36M1 3/4 vacuum relief valve I plan on using is rated for 250 F. The code is not specific at all, which leaves me to believe I could argue just having one at all would satisfy the requirement.

P2804.7 Vacuum-relief valve.​

Bottom fed tank-type water heaters and bottom fed tanks connected to water heaters shall have a vacuum-relief valve installed that complies with ANSI Z21.22.

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Jeff H Young

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The way I read it the pipe going into the tank at bottom (actually second from bottom in your diagram) should be served by the VRV Id go on to recomend no shut off valve between that VRV and the tank and valve be at 6 inches above tank. Inspector seems to have an idea what he wants No idea where you are coming with 2 valves needed? run it by him
 

burto17rn

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The way I read it the pipe going into the tank at bottom (actually second from bottom in your diagram) should be served by the VRV Id go on to recomend no shut off valve between that VRV and the tank and valve be at 6 inches above tank. Inspector seems to have an idea what he wants No idea where you are coming with 2 valves needed? run it by him
I'm only running the one valve. I drew proposed locations on my drawings as part of me asking the question.
 
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Jeff H Young

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option 1 is definately in wrong location or could be argued it is wrong , as could option 2 but I dont see why 2 wouldnt work . but installed as I recomended I dont see issue . your installation requires it because its a water storage tank not a water heater so true there is no cold water but there is an inlett thats where Id put it , if I wasent going to inquire witrh inspector again .
Since you are submitting your drawing lets see what he answers back, I think its important not to have a shut off valve betwen the VRF and Tank.
 

GReynolds929

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Your drawing is wrong. The storage tank has a domestic input and output. You are showing heating in and out at bottom but only hot out on top. Heating side does not need a vacuum relief like fitter said. The vacuum relief is installed on the inlet to the tank, whether it's hot or cold doesn't matter.
 

burto17rn

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Your drawing is wrong. The storage tank has a domestic input and output. You are showing heating in and out at bottom but only hot out on top. Heating side does not need a vacuum relief like fitter said. The vacuum relief is installed on the inlet to the tank, whether it's hot or cold doesn't matter.
So create a loop on the inlet that extends 6 inches above the tank?
 

Jeff H Young

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I dont see why your option 2 wont work but since you already contacted the inspector any reason why you arent asking him again ? It wouldnt hurt to follow any referance to how to pipe relief valve in tank manufactures instructions?
Im assuming you want no problem with inspector I dont see where your option 2 is mentioned in the code so go for it and run it how ever you want or ask him but Id either follow the drawing that you referanced when i clicked on anzi 21.22. or get his blessing on doing it the way you want (option2)
I dont know how it was determined by fitter 30 that you dont need a vac relief valve . I suppose you could ivestigate that and challenge the entire idea of needing one?
 

Bgard

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It should go in the cold water supply line, some ware around the expansion tank. The the intent of the code is to prevent the water in the tank from being sucked out if the city supply pressure drops below 0, ( think fire truck pumper hooked to a hydrant nearby) they don’t want the water in your system (possibly contaminated) drawn into the main.
 

Reach4

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It should go in the cold water supply line, some ware around the expansion tank. The the intent of the code is to prevent the water in the tank from being sucked out if the city supply pressure drops below 0, ( think fire truck pumper hooked to a hydrant nearby) they don’t want the water in your system (possibly contaminated) drawn into the main.
I think a vacuum relief valve is to prevent the tank from collapsing inward.

A vacuum is more likely on an upper floor than in a basement.
 

Jeff H Young

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might be other reasons but i heard its to prevent tank imploding thats why if its in an attic or up high you put a vac relief
 

Jeff H Young

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For clarification this installation is on the first floor of a slab on grade home that is 2 stories tall.
Thanks burto17m I dont install many bottom fed that must be the reason Ill have to check if I have similar requirements here.
What did you decide on how to plumb it ?
 

burto17rn

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Thanks burto17m I dont install many bottom fed that must be the reason Ill have to check if I have similar requirements here.
What did you decide on how to plumb it ?
I'm going to put on top of the tank on the hot side where I have shown option 2 because it requires the least amount of rework. If he rejects it while will put it on the inlet side.
 

John Gayewski

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Very much over complicated a simple question. It goes on the cold. The hot side will get gummed up with mineral deposits. If the inspector will accept it then go with it, but when you go to empty the tank be aware that the valve may not work and be stuck closed. In that case open a faucet. It does the same thing.
 

burto17rn

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Very much over complicated a simple question. It goes on the cold. The hot side will get gummed up with mineral deposits. If the inspector will accept it then go with it, but when you go to empty the tank be aware that the valve may not work and be stuck closed. In that case open a faucet. It does the same thing.
So in my sketch you would put it on option 1? Thats the only cold water I have available.
 

Jeff H Young

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I did a little looking at hot water storage tanks and randomely looked at one manufacture and I would say follow manufacture instructions on how to pipe it your plan option 1 is close look it over with your instructions
 

John Gayewski

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It is for emptying the tank. Where the cold goes into the mixing valve is the best spot as long as the mixing valve doesn't have a check valve and the tank isn't seperated from the vacuum relief by a check valve.

Seeing as you really don't need one and are just installing it to satisfy the inspector I would ask him. But it should be on the cold.
 

burto17rn

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It is for emptying the tank. Where the cold goes into the mixing valve is the best spot as long as the mixing valve doesn't have a check valve and the tank isn't seperated from the vacuum relief by a check valve.

Seeing as you really don't need one and are just installing it to satisfy the inspector I would ask him. But it should be on the cold.
I had not considered that idea. Thank you for the suggestion.
 

Jeff H Young

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yes on a slab its not really needed however your code requires it as does the tank manufacture instructions ( I belive most manufactures have it in the instructions)
 
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