New gas boiler and gravity water

Boilerpro

> Pipe it P/S and you will have no <BR>
> problems!!<BR>
> <BR>
> Mark H<BR>
> <BR>
> _A <BR>
> HREF="http://www.heatinghelp.com/getListed.cfm?id= <BR>
> 238&Step=30"_To Learn More About This Contractor, <BR>
> Click Here to Visit Their Ad in "Find A <BR>
> Contractor"_/A_ <BR>
<BR>

Unknown

On a new install

of an atmospheric gas boiler on a grvity hot water system with huge pipes and cast iron rads - is it necessary to protect the boiler with some sort of bypass piping ? Since most of the new gas boilers we see come cold start , Im assuming they are built to withstand the condensation problems with temps below 130 or so ? On a system like this , is it a better idea to try to maintain a minimum temp and use a zone valve to regulate the flow ? Or just use a circ and flowvalve ? Thanks for any help .

ed wallace

gas boiler and gravity flow

i replaced a gas boiler 2 yrs ago it was the same situation as yours the owner of the supply house told me to add a bypass between supply and return he recommended a 1/2 bypass i tried it and it works something about condensation and protecting the boiler

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Mark Hunt

Primary/Secondary


Pipe it P/S and you will have no problems!!

Mark H

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Mike Kraft

Read some stuff.........

off the Wall Ron!Check heating q&a top left of this page.Below is from that!

Q: Where is the best place to install the circulator?
A: It's always best to put it on the supply side of the boiler, pumping away from the compression tank. Piped this way, the circulator will add its pressure to the system's fill pressure and make it easier to get the air out. The system will also run more quietly.

Q: Do I have to use a bypass around the boiler on these jobs?
A: Most boiler manufacturers recommend that you install a bypass around their new boilers when you use them on a gravity system. Here's what that bypass piping looks like.

The drawing didnt copy.........




Q: What's the reason for the bypass?
A: It's there to protect the boiler against condensation and thermal shock.

Q: What's thermal shock?
A: Thermal shock is what happens to hot metal when you hit it with relatively cold return water. If you take a glass plate out of the oven and run cold water over it, it will break, won't it? That's thermal shock.

Q: How does the bypass piping help prevent this?
A: The boiler bypass allows the majority of the return water to bypass around the boiler while just a small portion of that water flows through the boiler, picking up the necessary heat.

Q: You said something about condensation. What's that all about?
A: If the return water temperature is too cool, the combustion gasses can reach their dew point and turn into a liquid inside the boiler. That liquid is very corrosive to metal. It can damage or destroy a boiler in no time at all. By using the bypass, you're mixing hot supply water into the relatively cold return water and raising the boiler water temperature to a point where the gasses can't condense inside the boiler.

Q: Does the bypass serve any other purpose?
A: It allows the boiler to come up to high-limit temperature and shut off. Without the bypass, the large volume of water moving through the boiler often keeps the temperature low and prevent the boiler from reaching high-limit. This does a good job of increasing the fuel bill.

Q: Is there another way to pipe the replacement boiler without using the bypass?
A: You can use primary/secondary pumping techniques.

Q: What's primary/secondary pumping?
A: It's a way of treating the flow through the system and the flow through the boiler as two separate things.

Q: Is there an advantage to this?
A: There is because some boilers require a minimum flow to operate at their maximum potential. This flow may not be the same as the flow you need in the system. If you use a bypass line, someone may adjust it after you've left. This can cause problems with both the boiler and the system.

cheese

Steamhead

Ron, those huge pipes

have almost no resistance to the amount of water you have to move. It's very easy to over-pump such a system. You want to mimic the flow that would occur when the water in the boiler is maxed-out at 180 degrees.

The best sizing method for gravity conversions I've seen is the one B&G had in the 1940s. Go to http://www.heatinghelp.com/newsletter.cfm?Id=125 to access a chart based on this. Also http://www.heatinghelp.com/newsletter.cfm?Id=119 for the situation that inspired the chart.

I tried this on my own system. Replaced a B&G 100 with a Taco 005, now there's actually a noticeable delta-T across the system, and I was able to install a nozzle one size smaller and still get the same amount of heat.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Mark J Strawcutter

Right now I'm liking

primary/secondary with the boiler on the primary loop and the rads on the secondary. Primary should have system bypass (as opposed to boiler bypass) controlled by ESBE TV valve. ME posted a drawing of this setup a while back and the more I think about it the more I like it.

Mark

Unknown

Thanks guys for all the replies

This wasnt one of my jobs - a serviceman saw this situation at one of our customers houses . And he knew I used to install gas in a past life .

It was a gas Peerless MI series , one zone gravity . No bypass . Another question - if there was a bypass installed without any pump on the bypass or the zone , would it actually bypass , blending hot water with the return ? Is a Venturi tee needed to do it this way ? Thanks again .

Boilerpro

Say Mike, I've often wondered...

how bringing the boiler up to the high limit and cycling the burner will save fuel? The hotter a boiler runs, the poorer the heat transfer. The more the burner cycles, the lower the overall burner efficiency? Right? If we wanted hotter boilers, we wouldn't be using reset on the better jobs and we would want to oversize boilers so they would cycle off thier high limits. Was wondering the basis for this answer to one of the above questions.

Boilerpro