Expansion tank

[maplewoodshelby]

Folks its nearing the end of the wood burning season for me and this being my first winter with hydronic system installed I have a few questions for over the summer adjustments. My system did very well this winter heating 5000 sq ft and dhw. My neighbor and I did the install and thanks to this board did not spend a penny on labor.
A few questions:
I have a conventional indoor wood boiler that is piped into a gas boiler and then on into the house. The propane boiler was there when I bought the house so I decided to pipe them together in the event I would need it when away. My wood boiler outflow to the propane boiler comes out of the top of the wood boiler travels horizontal for 3 feet then turns straight down about 3 feet to go into the propane boiler. It then leaves the propane boiler, goes to a tee (1/2 copper goes vetical to expansion tank, 1 inch copper goes horizontal into the house for heat.)
I'm getting some air trapped in the propane boiler because everyday I can lift the popoff valve on the propane and get air for about 2 seconds.

My question is this. Should my expansion tank which is a 45 gallon solid tank be teed into my wood boiler outflow before it turns down to go in the propane boiler? I'm thinking this will fix my air problem and since my wood boiler is my primary heat it should be this way anyhow.
Will this affect my propane boiler operation. I do not run them together it is either one or the other and it will be rare that I run propane.
I did not have any pressure problems the entire winter but the air should not be getting caught in the propane boiler

 

[webie]

Seeing no one has answered yet I will give you my opinion . My original inside boiler was plumbed such as your wood to the gas and then out to the house and from the wood supply line before it turned down to the gas return there was a 1/2 T reduced to 3/8 then over to the expansion tank and T'd into the line comeing from the gas boiler going to the expansion tank .
Personally I would not do this this way as for what ever reason you seem to be generating a certain amount of air daily for you to be able to purge air off your gas boiler daily . I would install some kind of an airscoop self bleeder in your supply line comeing from your wood boiler .

 

[RobC]

how about a quick drawing of the pipe lay out....
Rob

 

[maplewoodshelby]

I'm not sure how to post a pic in the message frame. I have added it as an attachment so hopefully folks can open it and view and give their opinion

 

[WoodNotOil]

In a typical two boiler system, each boiler will have its own expansion tank, so you definitely need to put an additional one in on the wood. Pressurized storage also requires its own large expansion tank proportionate to the volume of storage. I am not sure of the calculation off the top of my head though. I will look it up if I get a second and post it to you. Here is a link that will give you an example of what I am talking about http://www.ekowoodboilerblog.blogspot.com/

 

[maplewoodshelby]

Thanks for the info. Like I said earlier, I had no problems the entire winter with pressure. The system stayed at 12 psi and never moved even when system was cold or running full bore. Do you still think that I need two tanks. I have no problem installing another tank but I dont see the benefit or how it can help or protect my system. My thought was moving it in between the two boilers to prevent air from somehow getting stuck in my propane boiler befoer entering the house. Maybe all I should do is add another air vent between the two. Any ideas on where the air could come from? I have no leaks

 

[webie]

In a typical two boiler system, each boiler will have its own expansion tank, so you definitely need to put an additional one in on the wood. Pressurized storage also requires its own large expansion tank proportionate to the volume of storage. I am not sure of the calculation off the top of my head though. I will look it up if I get a second and post it to you. Here is a link that will give you an example of what I am talking about http://www.ekowoodboilerblog.blogspot.com/

Unless somebody enacted some kinda law I beg to differ as each boiler needing its own expansion tank.
A expansion tank or multiple expansion tanks need to be sized according to volume of your system . I believe the rule of thumb is water will expand 4% so the expansion tank or tanks capacity should be 8-10% of systems volume as a safety margin . I ran for 18 years with a single expansion tank for my system of wood boiler and gas boiler . Its when I added the Tarm and another 2 zones that we added an extra expansion tank coming off of the tarm boiler because of the increased volume of water .
Most people adding a wood boiler into there original heating systems need to add an extra expansion tank because of the increas in water volume .

 

[WoodNotOil]

There is air in the water that enters your system and it slowly collects at certain points over time. Ideally it eventually works its way out of the system unless it gets trapped at a high point where there is no way for it to get to a point where it can be vented. If your expansion tank is undersized, there may become a situation over time that you can't predict where the tank will fully expand and then your system pressure will build until the relief valves blow. Just because it is working now does not always indicate that it is designed to handle the fluctuations under all circumstances... I am no expert, but I assume these design principles exist for a real reason...

 

[webie]

Thanks for the info. Like I said earlier, I had no problems the entire winter with pressure. The system stayed at 12 psi and never moved even when system was cold or running full bore. Do you still think that I need two tanks. I have no problem installing another tank but I dont see the benefit or how it can help or protect my system. My thought was moving it in between the two boilers to prevent air from somehow getting stuck in my propane boiler befoer entering the house. Maybe all I should do is add another air vent between the two. Any ideas on where the air could come from? I have no leaks

Where the air is comeing from was my original question ? But then in my original heating system I swear it took a year to get all the air out .
I would just add a airvent into the line comeing from the wood boiler

 

[WoodNotOil]

In a typical two boiler system, each boiler will have its own expansion tank, so you definitely need to put an additional one in on the wood. Pressurized storage also requires its own large expansion tank proportionate to the volume of storage. I am not sure of the calculation off the top of my head though. I will look it up if I get a second and post it to you. Here is a link that will give you an example of what I am talking about http://www.ekowoodboilerblog.blogspot.com/

Unless somebody enacted some kinda law I beg to differ as each boiler needing its own expansion tank.
A expansion tank or multiple expansion tanks need to be sized according to volume of your system . I believe the rule of thumb is water will expand 4% so the expansion tank or tanks capacity should be 8-10% of systems volume as a safety margin . I ran for 18 years with a single expansion tank for my system of wood boiler and gas boiler . Its when I added the Tarm and another 2 zones that we added an extra expansion tank coming off of the tarm boiler because of the increased volume of water .
Most people adding a wood boiler into there original heating systems need to add an extra expansion tank because of the increas in water volume .

You are probably right Webie. I am no expert on these things. I assume though that in some piping schemes where the boilers might run independently of one another, each having their own expansion tank would ensure that expansion can happen where the actual heated water is flowing. For instance, if he simply moved his to between the wood and gas boiler, then when the gas boiler is running and the lines that actually have the expansion tank are cold with no flow, it may become an issue?

 

[in hot water]

The best location in that drawing and installation would be just before the circ on the bottom. You always want to pump away from the point of no pressure change. The PONPC is the spot where you install the expansion tank. As long as the boilers cannot be valved off from one another then only one expansion tank is needed. Installing two, at separate connection point changes the hydraulics in the system. The system only needs, and wants one point of reference.

Better yet would be to move the circ up to the outlet of the second boiler with the expansion connection just before the pump. That way the pressure increase the circulator provides aids in removing air from the system and you provide a place to have air removal, expansion, and a fill valve all at the best location.n

The air elimination device should be at the hottest and highest pressure point in the system, the outlet of the second boiler. I'll bet those pesky air problems would go away if you properly locate the PONPC.

Series piping two boilers is not the best way as the unfired boiler is always being warmed by the fired one. A portion of the heat from the wood is lost of the second boiler. A bigger problem is when the backup boiler is warming the wood fired one and losing heat up the wood boiler flue.

Grab a copy of "Pumping Away" written by Dan Holohan, here is an intro to that concept and the engineer that realized the importance of expansion tank placement. www.heatinghelp.com/article/11/Hot-Tech-Tips/260/The-Point-of-No-Pressure-Change

or any of John Sigenthalers writtings, "Modern Hydronics" for example. Bell and Gossett also has good information at their website about expansion tank location. They all clearly explain the concept of installing the pump down stream of the expansion tank location.

hr

 

[webie]

In a typical two boiler system, each boiler will have its own expansion tank, so you definitely need to put an additional one in on the wood. Pressurized storage also requires its own large expansion tank proportionate to the volume of storage. I am not sure of the calculation off the top of my head though. I will look it up if I get a second and post it to you. Here is a link that will give you an example of what I am talking about http://www.ekowoodboilerblog.blogspot.com/

Unless somebody enacted some kinda law I beg to differ as each boiler needing its own expansion tank.
A expansion tank or multiple expansion tanks need to be sized according to volume of your system . I believe the rule of thumb is water will expand 4% so the expansion tank or tanks capacity should be 8-10% of systems volume as a safety margin . I ran for 18 years with a single expansion tank for my system of wood boiler and gas boiler . Its when I added the Tarm and another 2 zones that we added an extra expansion tank coming off of the tarm boiler because of the increased volume of water .
Most people adding a wood boiler into there original heating systems need to add an extra expansion tank because of the increas in water volume .

You are probably right Webie. I am no expert on these things. I assume though that in some piping schemes where the boilers might run independently of one another, each having their own expansion tank would ensure that expansion can happen where the actual heated water is flowing. For instance, if he simply moved his to between the wood and gas boiler, then when the gas boiler is running and the lines that actually have the expansion tank are cold with no flow, it may become an issue?

No issue , an expansion tank is just that , a place for your water to expand to .
If it is all said and true that his system has run at 12 lbs and has had no issues ,I would call the one tank good enough . I would cut a 3/4 T into the supply line from the wood boiler Go up a few inches to a foot with a 3/4 pipe and then put a manual bleeder on top there with a church key . I be willing to bet you burp this a few times a year after a couple of years the air will be all gone and it will be the last you will need it unless you drain and refill .
The other option is to put in an airscoop with an auto bleeder , This is the pricer way to go .
The one question I do have is how hot are you running . You dont want to run that hot that you are creating steam.

 

[maplewoodshelby]

Fellows,
I will take a picture tonight and add another more detailed drawing tomorrow. My drawing is a liitle off and I want to get it right. This info is moving me in the right direction so check back tomorrow. This has baffled me all winter