i am in the finishing stages of hooking up my hydro heating sytem in my
new concrete floor. my system is a bit different than usual, as i have
no constant water feed to the system. i am coming out the drain in the
bottom of my hot water tank into my pump, and into the floor. out of
the floor, the flow goes into the air scoop, with the expansion tank
sitting beneath it, and back into the hot nipple on the tank. there is
a boiler valve installed at the bottom of the tank, before the pump, in
case i need to drain the tank. after the air scoop, before the loop
re-enters the tank, there are two boiler valves with a ball valve in
between. closing the ball valve will allow me to direct the flow into
one boiler valve, into the tank, through the system, and out of the
boiler valve on the other side of the closed ball valve, when filling
is there any reason i should be concerned about water loss in such a
system? i am using all galvanized steel fittings, with wirsbo aquapex
lines in the floor, so i'm not sure where could be a loss, except out
of the PRV in the event of the expansion tank not functioning properly.
which brings me to the reason for my question...
the problem i am having is how to determine how much pressure to have
in my expansion tank before i fill it. the directions are that it
should be set the same as the incoming pressure in the feed line, but
since mine is a closed loop system, i don't know what that pressure
will be. the pump says 125psi max., but i don't know how much it will
actually be putting out.
You have a closed loop hot water heating system. You need both a
temperature and a pressure gauge. In a system of this type, 30 PSI is
the maximum pressure. You must install on the boiler a relief valve set
to this pressure. Operating pressure need be no more than 12 PSI for up
to a two story building. You can use a PRV designed for heating systems
(such as B&G) that will keep your system at 12 PSI or you can hand feed
by periodically checking the pressure. Many older systems in the US and
new hydronic systems outside the US are hand fed. Barring leaks, there
is no reason to keep feeding water. A hand feed has the advantages of
letting you know there is a leak because pressure drops and a hand feed
also prevents a flood should the system leak while you are away. The
pre-charge on your expansion tank should be the same as operating
pressure (12 PSI if you are taking my advice). Expansion tanks made for
heating use are designed to survive 200 degree F temps of some heating
systems, but since you are doing radiant and your operating temps
shouldn't go over 130 you should be OK with your domestic hot water
When in doubt, be safe and call a professional to come over and look
over the system before you turn it on.
Agreed. Instead of "When in doubt, call a professional", I should say,
"Call a professional."
Also, rereading the post I see that Paul uses "PRV" for pressure relief
valve. In my post I use "PRV" for pressure reducing valve.
thanks for the advice guys (sans condescention from one of you),
i do indeed have my contractor coming over this week, and this system
is set up based on his advice and that of the radiant heating
specialists at Familian NW, where i got all of my supplies. i am indeed
"for real" (not sure why anyone would wast time making up a story like
i have seen systems as simple as this in operation, and from the
research i have done on this board and elsewhere on the internet, i see
there are loyal adherents to certain systems. the space i am heating is
small (385 sq. ft), and i want to do this as simply as is possible,
without being so stupid as to expect to be able to do something that
just won't work. hence my post.
i'm not certain how i go about setting the pressure in the system to
what i want (12 psi as you say). my pressure relief valve is a standard
type that comes with the HWT, and relieves pressure at 150psi (the
aquapex and all components are rated at least as high, especially for
the relatively low temperatures i will be running). obviously this
relief valve will not do what you are suggesting. please excuse my
ignorance...if i understood this better, i would not be asking. i don't
have a pressure gauge installed, and i'm assuming this is the only way
to know what the pressure in the system will be. however...am i
measuring pressure produced by the pump during operation, or the
pressure in the system when it is initially fed by the municipal water
supply? as the system is set up now, the temperature will be set on the
HWT thermostat. at the risk of sounding even more ignorant, i wonder if
you could explain where the pressure i'm regulating will be coming
from. as understand it, i have pressure from a flowing pump (pushing
the water through the lines and back up to the top of the tank), and
the pressure created by thermal expansion of hot water. i (apparently
ignorantly) thought my only concern with excessive pressure, is in
controlling pressure created by the expanding water. and this, i
thought, is the job of the expansion tank. is there something i'm
really missing here?
i will have a proffesional come out out to look it over before i fire
it up...but i want to undertstand it as well as possible before then.
so your patience with elementary questions and any help is appreciated.
Ned Flanders wrote:
Even though you are using a domestic water heater, and your system is
small, nevertheless what you have is a classic hot water boiler heating
system. Therefore, you must adhere to classic hot water boiler system
rules. Hot water heating system must not exceed 30 PSI. This means you
have to take out the 150 PSI T&P relief valve and replace it with a 30
PSI pressure relief valve of BTUH rating equal to the energy input on
your boiler. The rules also state that you need a pressure gauge and a
temperature gauge on the boiler. Since you are not using the top cold
tap you could put a tee in here AFTER removing the dip tube.
Because you have a closed loop system with an expansion tank, pressure
is regulated by how much water you put into the loop. To raise the
pressure simply add more water. The circulating pump is there merely to
move the heated water around. The pump has nearly no effect on pressure
in the system. But you need a pressure gauge to know how much water to add.
thanks, mark. i will go get a pressure gauge today, and a 30 psi
pressure relief valve. i was under the inmpression that i would be
filling my tank and system completely, hence my misunderstanding with
the amount of water to add. however, i'm still confused about where the
pressure will be coming from. as i add water to the tank and through
the system, the air scoop will be removing air as it passes by,
therefore also relieving what would be building pressure from the air
in the system compressing. i was told i needed to remove ALL air from
the system, which would not leave a variability in the amount of water
Mark Monson wrote:
---just came from talking with my "professionals." they concur that my
system is set up correctly. my pump is gravity fed (maybe i didn't make
this clear enough), as it sits below the tank, and is pushing the water
through the system, rather than pulling it back to the tank. therefore,
once my system is filled, working pressure is almost negligible. as i
believed, my concern is with the pressure of expanding hot water. they
told me to leave the tank at its 20 psi precharge, and that i only need
to be concerned that there is enough pressure in the diaphram to return
water once it contracts again. as this was my initial question, it
seems my problem is solved. thanks anyway, guys.
Did they come out and look at it? I don't trust you to just talk it over
"(sans condescension from one of you)," (spelling corrected)
well buddy I was not being harsh to you at all, in fact that was me being
nice. All I said was you should get advice from a pro. Tell me what is so
condescending about that??
You have actually said some things that just don't make much sense to me, a
IE ---just came from talking with my "professionals." they concur that my
system is set up correctly. my pump is gravity fed (maybe I didn't make
this clear enough),
your system is either gravity feed or you have a pump to circulate. you
don't have a gravity fed circulating pump. further more you do not set up a
radiant system to be gravity fed, which it sounds like you have not since
you mention a circulator.
also it sounds as if you did not understand the pressure issue. you
mentioned 125psi as if it was an acceptable working pressure for your
system. You sound like you think the pressure does not matter; "I only need
to be concerned that there is enough pressure in the diaphragm to return
water once it contracts again. as this was my initial question, it seems my
problem is solved. thanks anyway, guys."
Well how much is that? you could over charge it and still have this
condition. That is not the " answer to your initial question".
You have made some other mistakes as well sir and this is why I said "there
are a number of things in his post that make me think he should get advice
from a pro."
Do I need to go on?
If you can apologize then perhaps I will explain at least one of the
mistakes you have made and help you make it right.
okay, i am sorry if you were not intending to condescend. however, your
original comments weren't very helpful, as you just acted like i was
making my situation up or something.
anyway, my PUMP is gravity fed. that is, because i don't have incoming
pressure from a constant feed, i put my pump below the tank so it will
always be fed water. this then pumps the water through my system and
back to the top of my tank. i didn't say my entire system is gravity
when i went back to talk to the professionals who help me set up and
sold me this system, they concurred that there should be NO pressure
involved once it's filled, except the small amount of pressure created
by the circulator, and pressure created by thermal expansion. the
expansion tank was always intended to solve this problem. as i stated,
everything is rated for high P.S.I., though it shouldn't have any
reason to get up there. i thought about about it more, and realized
that maybe i would be beginning with pressure equal to the municipal
supply if i feed it until it is totally full, even if it is then
disconnected. otherwise, maybe you could explain to me where pressure
is created? mark mentioned that conventional boiler systems are usually
30 p.s.i max, and the "professionals" agreed, but said that since this
was not a conventional boiler, that it isn't an issue.
anyway, i'm interested to hear your feedback, but i'm apt to trust the
people i can talk to face to face who do this everyday. i don't mean
any offense or anything, but they are tangible and have seen and
reccomended this setup.
As Ned correctly noted, you came to us with some very confused ideas
about how hydronic heating systems work. After going back and
consulting your experts you are even more confused. When it comes to
hydronic heating, you and your helpers obviously don't know what you are
Instead of playing around with dangerous central heating equipment you
ought to apply your modest talents and very limited knowledge to
something less challenging. Perhaps you can tackle the assembly of a
child's swing-set if you follow the directions to the letter. If
confused contact the newsgroup: alt.DIY.dipshit.
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