Hot Water Tank__Radiant

Tom Hopkins

I've never used a hot water tank as a radiant heat source. Builder wouldn't go with regular boiler and the plumber won out. Plumber has hooked up the system and hasn't returned back to the job. I think it was the first he has installed also. Wood floor is going in and builder need to heat concrete. The problem is at cold fill, pressure is at 12 PSI, as the tank warms, pressure climbs, increasing to 30 PSI. If the circulator is turned off, heating just the water, pressure climbs even faster. I see that the circulator is pumping towards PONPC. What could be the problem and how is the correct way to pipe a hot water tank to radiant floor? I'm thinking to change location of ex.tank and the cir. pump and and installing a mixing valve.

Jack

jp_2

expansion tank

not working or too small.

Rich Kontny_3

Has to be....

That is a large volume of water in a closed system! Before you change anything have the builder or owner sign off on liability! If the plumber didn't size the exp. tank right he probaly screwed up loop lengths etc. You could be setting yourslf up for headaches if you start changing this system.

I hope you mean't rv(on the side of the tank) if there is no relief valve RUNNNNNNNNN!

Rich K.


Make Peace our Passion while Supporting our Troops!

hot_rod

Check the pressure

the precharge in the tank. What size circ? It would be better to pump away from the expansion tank. The expansion tank needs to be sized to the system volume and delta t, etc. I'd guess at least a #30.

hot rod

lee_7

Are you in Buckingham, Pa?

Tom Hopkins

Thanks

House is an existing after the War (WWII), 950 sq ft copper lines in concrete north of Chicago. Now in the stages of remodel, up and out. I was there yesterday for a short period of time, before no heat service calls, called me away. I did notice he used a PLT-5 Potable water ex tank. on lines. I'll change that to a ET-30 Watts or other. Thanks for responds

Jim Hankinson

If it's a potable water tank probably has a pre-charge of 40psi.

Dave Yates (GrandPAH)_8

the tank

is undersized and most likely has a 40-PSI air charge. Even if you lower the air charge to 12-PSI, it remains undersized for the amount of thermal expansion you'll get when raising the water from 60F to 140F. If you start at 12-PSI air-charge & that matches the system's pressure, you'll halve the volume in the tank and double your pressure. That's assuming the tank never loses any air or that the PRV never sees a spike in the house pressure to add water over the initial 12-PSI. Or that the PRV isn't momentarily fooled by the pump's activity and subsequent drop in PSI at the PRV's connection point.

Rob Blair

I never thought about the size of the tank in relation to the...

volume. Do you take the 40 or 50 gallon tank as part of the volume? I just finished a 500 square foot slab job and used a #15 tank and the heating unit was a 40 gallon gas power vent. I noticed the pressure running up in the low 20's. I checked the static pressure on the tank prior to installation and it was 12#. Would the volume of the water heater make the tank too small for the system?

I did have a 30# relief valve installed.

Rob