Bypasses

todd s

I was discussing this with a friend and we were unclear as to the reasons for the two different ways to pipe a bypass. One is the boiler bypass and the other is the system bypass. What is the main difference between these two? What situations would either be used for?

Dan Peel

my take

A boiler bypass delivers the full flow of the combination of circulation and piping through the distribution system while allowing a boiler to attain/maintain a higher fluid temperature. A system bypass acts to maintain full flow through a boiler while delivering a reduced flow volume through the distribution piping. Cast boilers care very little about flow rate and can benefit from boiler bypass by getting above condensing temperatures quickly even in high mass distribution systems. System bypass is useful for blending return water temps up for boiler protection, increasing temperature drops across exchangers or controlling flow rate related noise. Enjoy.....Dan

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todd s

Bypass

Thanks Dan. Now assuming the typical pumping away piping method, if the bypass is a tee after the circ going into the return is it a system bypass? And if the return is tee'd in before the circ its a boiler bypass? We were discussing this in reference to cast iron oil boilers connected to large volume systems such as old cast iron radiators.

Dan Peel

Yep

You got it. For good boiler bypass piping diagrams look at Burnham's suggested piping for their oil fired boilers. Enjoy....Dan

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todd s

Thanks Dan

I was trying to get into the Burnham website earlier but was having a problem and I knew this would be the place to ask.

Weezbo

notice the use of the by pass......

i try now that it seems unclear... pump on the return,radiant loop some place...by pass on boiler comes back ahead of a temp gauge abobe the "pump" after the checked return from the radiant. this mixes the return temp UP to say 140,straight from the supply to the T in the return ahead of the temerature gauge.
.... system by pass,....way out in the field you have a Radiant "Header" both supply and return, cut a t into both the supply and return connect them,place a valve on the connecting piece,now when the cool water "comes back" through the radiant,it mixes with Hot supply water UP .temperature guages are good as it allows dummie bypass valves to be set some what near what you may want the return temp to be. now you have the gist of it...you can use fixed mix, porportional fixed mix,modulating mix,variable modulating....all similar, each with its own bennies:) and each can be used in conjunction with each other each with its own bennies. while some dissagree with one minor technicality or another,i am gonna make this special Leap of faith in saying ANY mix is better than No mix. so as my dad used to like to say "You gotta Mix it Up some in Life"

todd s

mixing

I agree with you about mixing. Every one we've piped this way burns cleaner and has far less scale on the fire side. We were trying to decide which was better for a particular situation.

Unknown

Bypasses

In answer to your question, quite simply, a Boiler Bypass lets system return water bypass the boiler, thus reducing the flow of return water through the boiler and allowing it to heat quicker. There will be a reduction in system water temperature based on the amount of water bypassed and the boiler limit. A System Bypass lets heated boiler supply water bypass the system by sending it through the bypass to the boiler and system return. The result here is warmer boiler return water at the sacrifice of some flow to the system.

We advise using a Boiler Bypass on all of our boilers with the exception of the LE and LEDV boilers. These horizontal tube style boilers need to remain warm on the return side due to the scotch marine style construction and therefore nees a Syatem Bypass. What makes one bypass different from the other is the location of the system pump. In a Boiler Bypass application, the pump is always on the system side of the bypass and in a System Bypass application, the pump is on the boiler side. Hope this helps.

Glenn Stanton

Manager of Training

Burnham Hydronics

hr

Bypass piping

is not always a good mix with radiant floor heating. It has no "smarts." In other words it cannot see, or sense what that return temperature is. So it may or may not be giving you adequate mix, or protection.

In a high mass radiant (concrete slab) this is a critical detail. A bypass pipe, even a bypass pump may not offer the protection you need. Plenty of inexpensive way to offer that function available on the market.

hot rod

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todd s

hotrod

We are doing alot of replacement of oil fired cast iron boilers connected to either high mass radiators or to fin tube baseboard. What I'm trying to do is add a bypass to most or all of the jobs in order to prevent condensation and shock issues. I wouldn't be opposed to any ideas you give, your opinion carries alot of weight.

todd s

Glenn

That's exactly what I was looking for. Is this diagram on the Burnham website?

Dan Peel

click it

Right click the image and then save it as a jpg to your hard drive for further reference..
Dan

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hr

Todd

in your case, and example, a bypass may be the ticket. And certainly much better to have a bypass on a high mass radiator piping than nothing at all!

I cautioned against a bypass for radiant more in response to Weezbo reply, as I understood him to say a bypass for radiant application mixing. Maybe I mis read his post, sorry.

hot rod

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Unknown

Glenn

I replaced an old gravity boiler last week with a V84 . The system had 2 - 2 1/2 inch headers and returns on one zone . I installed a boiler bypass on the system . Is the boiler
bypass a better choice than a system bypass in this application ? When is a system bypass a more suitable choice ? Thanks in advance .

Unknown

No

These are drawings that I did for my seminars. Our Installation and Operation Manuals show Boiler Bypass piping and they are downloadable from the Web. Hope this helps.

Glenn

Unknown

Ron

I did see that post but was out of town and didn't spend much time on line that night to comment. In my opinion, for what it may be worth, I believe you will be better protected on a gravity conversion with a System Bypass because you are keeping the boiler warm or hopefully hot. The reduced flow to the system you may encounter will probably not be a concern provided you keep the boiler hot enough to keep the heat flowing. Here is another method that the Hydronics Institute recommends using which is in essense very close to the way you piped yours or a boiler bypass. My concern about this piping is the effect of large amounts of cool return water on the boiler. This graphic is from their GAMA I=B=R Guide. Hope this helps.

Glenn

Unknown

Bypass piping

is only a bare bones way of helping to provide boiler protection. In some cases where return water is not real cool and system flow is not variable, it will suffice. Better methods involve Primary-Secondary system piping, Primary-Secondary Variable Speed Injection, Modulating 3 and 4-way valves and better yet Primary - Secondary Boiler Injection with a Boiler Return Sensor. Here is a method we provide and advise using on our Commercial boilers or the Return Temperature Control (RTC). This setup allows the boiler to work well even with FULL system temperature reset. Hope this helps.

Glenn

Weezbo

Todd....

seeing as how we are now discussing mixers and mixing it would be unfair for you not to hear this phyliosophy from one of the Steam heads... steam heads had a heck of a good idea or two:) hang in here a while,,... forget recirculation pumps,variable speed,modulating motorized mixers,return temperature sensor control for a while and think about Thier savey on a bypass...one of them will come along soon and see your post. thier fixed bypass was a pinner little pipe:) i t shows you the limitations of the fixed bypass yet it aslo makes it real clear that was a definite step in the right direction .it is not a bad idea:)and i think you are on the right track there are lots of kinds of boiler protection all hooked up to that central idea. I am not reccommending using a fixed bypass for some multi zoned radiant . hot rod is correct it doesnt necessasarily provide adaquate boiler protection. how ever dont write fixed by passes off just yet.it appears that it would indeed be a leg up on the previous lash up. i have used them for years decades even never lost a boiler never lost a slab never lost a station . i will be honest here, i havent installed a boiler without a bypass in decades...some are based on different needs say and behave differently some have tec mar some have viessman some have buderas some have erie some honewell some taco wirsbo conrols and various pipeing modulation 3 4 way porportional ,pumped and yes fixed mixes. did i miss anyone here ohki doki Heat Exchangers, there is the double coil indirect that i havent given a go and a method that uses a 4 way fixed mix that isolates the boiler and primary without a boiler recirc...thought of it alot though. the caleppi mixerthing ,the grunfoss pump plan also interest me. i havent gotten my hands on them yet (well the calleppi thing whizzed past a while ago,) they too might be useful in certain applications:) the caleppi controls might be kinda useful so are Speed drives Speed drives can be cool this winter i put a small speed drive on a boiler i had basically heating alaska in 47 below zero ) ah it was a wash:)i couldnt tell if it was doing any good or not ))Didnt lose the boiler though:) hard to say whether the undersized supply lines to the unit heaters were protecting it the 4 way mixer or the speed drive none of which were lashed up in any kind of form previously seen by mankind:))))) we called the boiler stand the titanic as as it melted the clumps of snow and ice it kept sinking into the gravel:)no garage doors no insulation in the place some visquine draped vicariously about the walls and ceilings anyone ever tell you a slant fin isnt a tough chunk of iron they havent seen the testing labratories on the Last Frontier:) and hey let me chirp up wirsbo and rehau I lashed the unit heaters up with when it was so fricking cold in the building their combined R & D depts couldnt duplicate the environment:))))