more in floor heat Q's

[ModSquad]

Hey guy's,

I've read alot on the setups, I just had a few questions that I didn't see listed anywhere..

1. When running in floor heat on a slab on grade, with an electric water heater, why do you need an expansion tank? wouldn't the water heater do the same thing storing the hot water? If I look at the hot water system of the house, I don't see one.

2. In a closed system(with above mentioned hot water heater), do you necessarilly NEED the check valve? Hot water out the top of the tank and into the bottom of the tank. pump flows 1 way, I can't see the water stopping direction of flow. (It's not like I'm running a boiler where you need a mixing valve or zone to cool the water down a bit). If I look at the hot water system of the house, I don't see one.

3. is an Air scoop necessary? or is it just something to ease the mind? if the system is properly bled and pressurized, there shouldn't be any air in there.. and no leaks, is there another way for air to get in I'm not thinking of?

4. Ideally, we should be running moderate heat out of our heaters for the slab. What heat are you guys running at? What pressure are you running your systems?


I'm seeming to not be able to come to a decision on how I want to plumb it.. I guess I'm **** and want it to look clean. Can some of you post pics of the plumbing Jobs you've done? also note if it's single or multple Zones.. (I'm sure I'll be able to tell by looking ,but just curious).. mines a single zone 4 small loops.


Thanks guys , I haven't seen any of these questions.. they are just done, I was more curious as to the why's. (I like understanding what I'm doing then just doing it cause thats the way it's done. .)..

 

[ModSquad]

Here's a good read on expansion tanks and their uses.. how to select the proper size tanks also.. Don't get me wrong,I understand how water expands when heated and that water is not compressible hence the need for the expansion tank, however why is it in my 30yr old bungalow, there is no expansion tank installed in the plumbing line? I've also seen this in just about everyhome...

http://www.blueridgecompany.com/documents/Watts-ThermExpansion.pdf

It states in the beginning that it's

 

[wmonroe]

I agree with your line of thinking as my 50 year old house has never had an expansion tank and has never had any problems. Shouldn't the pop-off valve on the hot water tank prevent over pressurizing the system?

Will

 

[kbs2244]

Yes to both of your questions.
And your boiler systems also have a "make up' water system that takes new water into the system when it cools down after blowing off the expanded water.
New construction does have expansion tankes in the domastic hot water system. Before they would just let it get pushed "backwards" into the supply piping. But that wastes a lot of heat.
The check valve is there to prevent the same kind of "backflow" from your slab system. Your pump isn't running all the time and heat wants to go to cold. If your slab is warmer than your lines and tank the water will come back to it. Not stay in the slab to keep it warm.
There is a lot of stuff in a hot water system. It all has a purpose. Most of the needs were learned the hard way. When things didn't work and a reason and fix had to be found. Then on the next install they put in the fix before the problem and, guess what, the problem never shows up.
That is how "standard procedures" get devloped. You can learn a lot from other peoples mistakes.

 

[ModSquad]

cool, thanks for the info.. I was more less looking for the why's behind it. I like knowing why these things are needed so I can have a better understanding of the system. This would be my first plumibing Job so I like to make sure I understand before proceeding..

so does it matter where the Check valve is placed? before the "mechanical package" after? in the return line? etc? most install writeups show them placed after the (drain/fill valves, expansion tank, pressure gauge etc)..

Thanks again

 

[kbs2244]

You are streching my memory here and I should tell you to check the book, but off the top of my head I would say it is the last thing in the supply line.
The reasoning is that will be keeping the warm water in the slab that way.

 

[buddyboy]

why do you need an expansion tank? wouldn't the water heater do the same thing storing the hot water? If I look at the hot water system of the house, I don't see one.

you need an expansion tank in a closed system.

 

[ModSquad]

I got it all plumbed. thanks for the info.. put air in it to pressure test and the pressure valve is leaking air.. is it supposed to hold air? I know when purhasing pressure releif valves, they are either air or water.. would that make a diff for holding air for the test?

 

[Charles (in GA)]

Water is not compressible, so in a closed system, something has to give, something is going to leak, crack or explode, and you don't want that.

For many people, their regular house system is not a closed system, most older houses don't have any kind of regulator or check valve on the line in from the public water system. If the pressure gets too great in the system, the pressure just backs up into the incoming line. The water tower down the road becomes your expansion tank. Due to contamination concerns, many water systems began requiring a regulator and a check valve, so that if they switch you to a different water tower with more pressure, they won't blow up your old water heater or start your faucets leaking. The check valve is a safety thing to prevent possible contaminated water from your system from backing up into the public water system. Lets say you have one of those blue water things in the toilet, and you also have one of those defective design tank valves that when the public water system fails (main breaks, etc) then the blue water in your tank backs up into the water system and into the public water. They don't want that, so the check valve stops that from happening. However, it also means you need an expansion tank for your water heater, since your house system is now a closed system..........

Charles

 

[ModSquad]

thanks for the detailed explanation again Charles.. I can always count on you for that..

I completed my install.. it's a closed loop system(garage is it's own).. and single zone(small garage).. I isntalled the airscoop and air eliminator for insurance of keeping air out of the system.. for the extra 80$ might as well.. also I installed the expansion tank. I'm using a tankless electric heater so I figured I'd need the expansion tank. If I was goig to run the electric domestic water heater(normal ones with tank) I wasn't going to use it due to what you mentioned above.

pressure testing it is a pain in the **** as the relief valve only seals 1 way, so the side of the return it leaks air as there is no seal. I think the air eliminator is leaking too as its only a small plastic plug that seals it. I'm going to pressurize it on my next day off and check all the joints with water and soap. hopefully I don't find any leaks.

 

[HoosierBuddy]

IIWY I'd read my electric meter every day and make sure I got a good handle on how much power is going to cost without waiting for a wake up call from the power company.

If the water heater can't recover, it's going to spin the meter about 4KW per hour. Round here, that would be roughly $7 to $8 per day. Hopefully it won't have to run all the time. Just something to watch out for.

Phil

 

[ModSquad]

yeah I know.. I figured it'll run lots to get the slab up to temp, but then after should be ok... it's BTU rating suites the size I have.. and I can run it off 30Amps.

Just curious, know of anything I can use to read the draw from this unit without looking at a meter?

I do have a 50Gal water heater that I can use just in case this one is too much $$