closed-loop hydro radiant floor system

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 expansion tank.

When in doubt, be safe and call a professional to come over and look over the system before you turn it on.

MM

I don't think that guy is for real but... If you are then you absolutely need to have a pro come out and advise right away, you might benefit greatly from his advice.

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.

MM

there are are number of things in his post that make me think he should get advice from a pro.

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 this).

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.

mark, 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.

MM

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 to add.

Mark M> > thanks for the advice guys (sans condescention from one of you),

---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.

The expansion tank has a diaphragm that separates the air cushion from the system water. It is this air cushion that allows for thermal expansion and contraction of system water.

MM

Did they come out and look at it? I don't trust you to just talk it over with them.

"(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 professional.

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 fed. 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

by the way, here it is:

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 talking about.

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.

MM