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Old 11-13-2008, 10:57 PM   #1
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Draining and then filling and bleeding system


Hello, I am going to be connecting a wood furnace to my Crown Boiler with a plate heat exchanger and would like some info on draining and filling back the system and then bleeding the air out. My system uses three zone valves on the return line, sends hot water to water to air exchangers in the attic via pex tubing and then heats the house with forced air (hydronic heating), the circulating pump is on the return line after the zone valves, there is an expansion tank on the hot supply line, an automatic low water cut off switch on the supply as well .
I first need to drain my boiler, to do this I believe that I just close the supply line and open the drain at the bottom of the return line. After connecting the plumbing I believe I just open the cold supply line and the automatic low water cut off should fill the system. I do not think there are any bleeder valves on the pex tubing or in the air handlers in the attic. There is a gateway valve on the return line before the three zone valves and on the bottom of the return line after the zone valves before the pipe enters the boiler. I think the only way to bleed the air out of the system is with the gate valves. There is also something ontop of the expantion tank that has a valve like what you see on a tire that I think is for bleeding, but I am not sure.
Any advice on how to do this would be greatly appriciated.

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Old 11-14-2008, 10:20 AM   #2
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Draining and then filling and bleeding system


This is a complex system and you might be in over your head. The biggest clue is that you are not sure what the valve is on top of the expansion tank.

But here goes.

First off does your system have antifreeze in it? if so you need to take precautions to contain it. While it is most likely propylene glycol as opposed to ethylene glycol and rather benign you should still make an effort to contain it.

Make sure the system is off. Draining a system is dangerous when the water is hot.

Open the valve at the lowest point where you intend to drain it out. If the system has any pressure in it (which is should) then this will release the pressure.

Then open up the highest point. This will prevent any water lock that could let loose at any minute and drain the rest of your system when you least expect it.

Then make your addition and close it up. Start putting in the water/antifreeze and look for a bleeder at the top of the system which can be a valve. If you don't have a bleeder then you should have an air scoop to get rid of free air.

It's important to get most of the air out as air will cause your pump to cavitate and damage it.

Before you drain your system look at your pressure gage and write down that number. Make sure the pump is off when doing this. This will be your target pressure when you get the system back up.

The tire valve on the top of the pressure tank is for putting in air to maintain a steady pressure. Use a hand pump like a bicycle tire pump to put in enough air to get the pressure up to what it was before your modifications. If you don't have enough pressure then your pump will cavitate.

If you have enough valves that will isolate the area you want to insert the additional hot water then you can use that and not have to drain the rest of the system.

Not sure if I covered it all but this is the general idea.

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Old 11-14-2008, 02:25 PM   #3
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Draining and then filling and bleeding system


Thank you for your reply. The valve on top of the expansion tank is an air scoop, it looks just like a picture in a link you sent someone else to that asked about air scoops, it looks like the second pic down and on the right column, except that it has the tire valve on top. The problem with that is the valves are meant to keep air in and not let it escape?
How do I add antifreeze to the system? Does my system defiantly have antifreeze in it? Can I test some of the drained water with a tester that is meant for a car?
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Old 11-14-2008, 03:08 PM   #4
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Draining and then filling and bleeding system


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Originally Posted by Nat1020 View Post
Thank you for your reply. The valve on top of the expansion tank is an air scoop, it looks just like a picture in a link you sent someone else to that asked about air scoops, it looks like the second pic down and on the right column, except that it has the tire valve on top. The problem with that is the valves are meant to keep air in and not let it escape?
How do I add antifreeze to the system? Does my system defiantly have antifreeze in it? Can I test some of the drained water with a tester that is meant for a car?
Do you live in an area that is prone to freezing? Is the system outside or in an unconditioned space?

Then you probably have antifreeze. It is the same stuff that is in the car radiator.

An air scoop on top of the pressure tank? That is a new one on me. There is supposed to be air in there and removing it negates the reason for the tank.

I guess I can see how the could make one that has a pipe that goes into the take half way down and will only remove excess air and combines with an air scoop. Actually that is a brilliant idea. I have just never seen one. Can you send me the manufacturer and post a picture.
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Old 11-15-2008, 06:07 AM   #5
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Draining and then filling and bleeding system


Sure I will send a picture, it will take a couple of days, Im not home right now.
I live upstate New York the temp in the winter gets below freezing at times, the boiler is in my basment. Is is possible there is no antifreez in it. If I need to add antifreez how can I do that? Can I pump it in the return line? How much would I put? Thank's again.
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Old 11-15-2008, 08:03 AM   #6
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Draining and then filling and bleeding system


I did some research on your setup. It appears that you have a combination air scoop, pressure tank and filler all on one connection. From what I can see of this setup you probably don't have any antifreeze.

If you intend to plumb in a wood heater that is outside then you will have to do some changing on how the system is configured and add some antifreeze.

Upstate gets pretty cold and you would have to have at least a 50/50 mixture that would put you in the -40 protection range. Depending on the product you might have to add even more.

It appears that you might have an automatic filler and would have to remove that to keep the antifreeze from getting into your water lines which is a bad thing.
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Old 11-16-2008, 04:28 PM   #7
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Draining and then filling and bleeding system


Thank you for spending time on researching my system. I did not think that I would have to change my system setup at all because I am keeping the two systems separate by using a plate heat exchanger. The two fluids will never come in contact with each other.
I also thought that the system would build up its own pressure due the the fact that it is a closed system, and that I would not have to manually add pressure to it, am I wrong? You mentioned something about adding pressure to the expansion tank, is that necessary or will it build up pressure on it's own? "The tire valve on the top of the pressure tank is for putting in air to maintain a steady pressure. Use a hand pump like a bicycle tire pump to put in enough air to get the pressure up to what it was before your modifications. If you don't have enough pressure then your pump will cavitate." Thank's again.
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Old 11-16-2008, 05:16 PM   #8
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Draining and then filling and bleeding system


It all depends on the tank. Some are open and have to be adjusted, some have bladders in em and don't need much adjustment. Some are already pressurized.

I have no idea which one you have. But if the pressure is low you can just pump it up. If it doesn't have any air in it then there will be no pressure regulation and pressure will fluctuate wildly depending on pump and temperature. This is why you record your current pressure to make sure that when the water is cold and the pump is off you can see what the base line pressure is. Some times you have to add air and pressure. The reason I tell people to use a bicycle pump is that I have seen them go wild and put in too much pressure with a compressor and blow out the system.

If you are putting in a whole new system why are you considering draining your existing system? I was under the impression that you were going to tie it into the existing system.
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Last edited by Marvin Gardens; 11-16-2008 at 05:18 PM.
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Old 11-17-2008, 12:02 AM   #9
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Draining and then filling and bleeding system


My exising boiler runs on propane which is very expensive, Buy connecting a outdoor wood boiler with my indoor boiler I can heat the water in the indoor boiler with wood that I can get for free, or at a tenth of the cost of propane.
I need to drain my existing boiler because I need to connect the hot supply line from the wood boiler to the hot supply line of the propane boiler, and if I donot drain it first there will be a big mess.
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Old 11-17-2008, 01:12 AM   #10
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Draining and then filling and bleeding system


So water from the wood stove will be mixing with the water from your propane boiler from what I can see.
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Old 11-17-2008, 02:58 AM   #11
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Draining and then filling and bleeding system


I will be using a plate heat exchanger with a wrap around pump. It keeps the two fluids completly seperate and makes it possible to keep the indoor boiler presserized and the outdoor boiler unpressureized.
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Old 11-17-2008, 08:02 AM   #12
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Draining and then filling and bleeding system


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I will be using a plate heat exchanger with a wrap around pump. It keeps the two fluids completly seperate and makes it possible to keep the indoor boiler presserized and the outdoor boiler unpressureized.
I see.

Still don't understand why you need to drain the pipes in the current system. If you are building the new system why not just work around the old one?

You're going to need antifreeze for the new system.
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Old 11-19-2008, 11:29 PM   #13
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Draining and then filling and bleeding system


The new system works in conjunction with the existing system, the existing system becomes the back up. In order to connect the two systems I need to cut a pipe on the existing boiler's supply line and add a tee to it, I thought that when I cut the supply line all the water above that point would drain out of the cut.
I took pictures of my system and was going to upload them to the chat room but when I tried to log on earler today, the web site would not let me send any replys. Now I am away from home untill saterday after noon.
I have a question about the air scoop ontop of my expantion tank. Using a mirror I was able to see the back side of it( there is only six inches between the back of the valve and the wall) it had an arrow pointing away from the boiler. The question is does this arrow mean that the air scoop will not allow any back flow of water? I intend to splice in the tee only 8 inches before the valve on the supply line and if the valve does not allow back flow then I do not have to drain the whole boiler because there would only be a little water loss.


Last edited by Nat1020; 11-19-2008 at 11:46 PM.
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