New NG hot water furnace: what's a correct PSI and also how to un-airlock a radiant floor

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edronline

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Got a new hot water furnace installed a few weeks ago (Weil-McLain EVG220, natural gas) along with a new expansion tank in a very old but well insulated and tall 4 story (including basement) house here in the north east US.

The techs filled the system to about 14.5 psi, and while the third/top floor radiator had water/heat, the strength of the stream coming out of the relief valve was weak (not a prostate problem, grin), and 2 second floor rads (right next to each other, at end of loop) had airlocks (this is common with them as it's happened before when prior system was drained/refills) so I added water to increase the pressure to 17.5 psi when cold and this took care of the strength of stream on the 3rd floor as well as the 2nd floor airlocks. (side note: I think there's a T junction below the floor which traps air since the rads are right next to each other on opposite sides of the same wall. bad design...)

The relief valve hasn't blown since I added the water. Is 17.5 PSI while cold an ok PSI for the system? I've found that when techs come to my house they tend to underfill the system. On the old Burnham, if I overfilled, the relief valve would take care of the pressure overload for me.

Also, yes, no air anywhere else in the system (i've checked all the relief valves on the rads) except for a stupidly installed (30+ years ago) radiant floor -- it's airlocked. It's very close to the furnace, but at the end of a loop. It's happened before when they've had to drain/refill the prior Burnham system.

Last time it happened a tech came out and said "since there's no access to the floor and no relief valve, I closed the other zones and the rads attached to that loop and just slammed water into it." eventually the floor started working again/water circulated. Is this a good idea to do, or will I over pressurize the system if I try to add more water into it? or does it even matter b/c the relief value will just do the job if I overfill?

thanks!
 
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Fitter30

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Height of the water is 2.31 ' per lb. So your 17.5 lbs cold is good. With the expansion tank replacement it probably a bladder tank that needs the air charge adjusted to match the cold boiler pressure for proper operation. By just running the pumps air eliminating devices should take care of getting rid of the air. Like to see how the radiate floor is piped off the main piping because the y should run off different temperatures.
 
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edronline

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@fitter30 thank you for your reply.

Yes, it's a bladder tank. How do I go about adjusting the air charge? Is this something I can easily do?

It's unclear how the radiant floor is piped off the main piping, unfortunately, since it's all buried in the ceiling. It's part of a run that goes off the main boiler, to a large traditional rad in the living room which is very long and squat and had 2-3 junctions coming off the main pipe to feed it (it's in a large window seat type contraption that runs the length of the living room) and then disappears into the ceiling where the radiant floor is. The loop is very short overall -- maybe 30 feet total from the furnace to the radiant floor. but it's a bad design.

I'll just hope that over time as the furnace works it pushes whatever air is in there out and the radiant floor works again!

my expansion tank is a EX-60 Amtrol btw.

Edit: I think I figured it out. I turn off the water to it, unscrew it from the system, make sure it is empty. then make sure that the pressure in the expansion tank = the PSI of the system (17.5). If it's low, pump it up, then reattach. seems pretty simple. I learned something new today!
 
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Dana

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A fine-tuning of the pre-charge pressure (not usually necessary) would be to account for any vertical distance between where the pressure is being measured vs. the elevation of the tank. In most installations it will be less than 5' difference (~<2 psi), and if the tank location is higher than the pressure gauge location the pre charge would be 1-2 psi too high, which is not enough to create any issues. At 10' or more difference it's best to adjust accordingly.

Also measure the vertical distance between the pressure gauge and the top of the highest radiator on the system to the nearest foot. The proper cold pressure on the system would then be vertical feet x (1/2.31 ) (= vertical feet x 0.433 psi), plus another ~2-3 psi to account for pressure differentials created by pumping. (For some 1-2 story houses or houses with the boiler located on an upper floor that calculation come to <10 psi, in which case the pressure should be bumped to 12 psi at the boiler to avoid flash-boil on the heat exchangers inside the boiler.) So a cold preset of 17.5 psi should be good for a vertical distance of (17.5-2)/-0.433= ~36' between the pressure gauge and the top of the highest radiator.

If the system is currently working and there is at least some vent or air scoop air purging device on the system it will eventually purge the remaining air, as long as the operating pressure meets the above criteria. There is no advantage to going higher than 2 psi + (vertical feet x 0.433). The higher you go with system pressure, the less working margin you have at the pressure relief valve.
 

edronline

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A fine-tuning of the pre-charge pressure (not usually necessary) would be to account for any vertical distance between where the pressure is being measured vs. the elevation of the tank. In most installations it will be less than 5' difference (~<2 psi), and if the tank location is higher than the pressure gauge location the pre charge would be 1-2 psi too high, which is not enough to create any issues. At 10' or more difference it's best to adjust accordingly.

Also measure the vertical distance between the pressure gauge and the top of the highest radiator on the system to the nearest foot. The proper cold pressure on the system would then be vertical feet x (1/2.31 ) (= vertical feet x 0.433 psi), plus another ~2-3 psi to account for pressure differentials created by pumping. (For some 1-2 story houses or houses with the boiler located on an upper floor that calculation come to <10 psi, in which case the pressure should be bumped to 12 psi at the boiler to avoid flash-boil on the heat exchangers inside the boiler.) So a cold preset of 17.5 psi should be good for a vertical distance of (17.5-2)/-0.433= ~36' between the pressure gauge and the top of the highest radiator.

If the system is currently working and there is at least some vent or air scoop air purging device on the system it will eventually purge the remaining air, as long as the operating pressure meets the above criteria. There is no advantage to going higher than 2 psi + (vertical feet x 0.433). The higher you go with system pressure, the less working margin you have at the pressure relief valve.

Thanks. Expansion tank is exactly at the level of the pressure gauge.
 

John Gayewski

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What the techs did was correct. If you shut the rest of the system and leave the radiant on, it will increase the velocity of the water and push the air out of the radiant loop.

Eventually the radiant could start working on its own, but no telling how long this will take. If the pressure in that loop is very low due to friction loss it could take a very long time or not happen at all.
 

edronline

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What the techs did was correct. If you shut the rest of the system and leave the radiant on, it will increase the velocity of the water and push the air out of the radiant loop.

Eventually the radiant could start working on its own, but no telling how long this will take. If the pressure in that loop is very low due to friction loss it could take a very long time or not happen at all.
It is working now! I'm happy. What seemed to help the most re getting the radiant floor and the stuck 2nd floor rads working was to up the pressure in the system (to something more reasonable for the height of the system to highest rad) and time.

Thanks everyone!
 

Jadnashua

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Radiant embedded in say a concrete slab could take days to warm up! So, without knowing more about how that was installed, hard to say. Glad it's working for you now...radiant floor heat is my favorite form as it's more comfortable and you don't have issues with furniture placement.
 
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