Piping Question

Tom_133

I have been doing primary and secondary piping a long time and recently needed to revisit the basics for a refresher course. I have found a lot of great info here on the wall, so thank you to all the many contributors. This is my first post and I have a question about branch sizes on primary secondary piping.



Scenario: Lets say we are installing a Baxi HT 380 and the primary header is 1 1/4" but the piping out of the bottom of the Baxi is 3/4. My thinking (possibly flawed) is that both tees on the Header that pick up the Baxi piping will be 1 1/4 x 3/4 tees, or shoud it be full 1 1/4 tees and run back to the boiler with 1 1/4 then reduce at the fittings?



It's always been my thinking that as long as the primary pipe remains the same size it doesn't matter what size you pipe into it, of course that comes with many caveats.

Henry

Pipe sizing

Boiler in/out size is irrelevant to the piping that goes from it. The piping must be sized according to the flow rates. As an example, Genoni heat exchangers of 399,000 BTU have 1 1/2 connections. For a 25 delta T we need 30 GPM.  1 1/2 pipe size maxes out at 25 GPM so we use 2 inch and reduce at the boiler.

B&G has a great easy tool called "System Sizer Calculator". It will give you Temperature difference based on GPM, pipe sizing  based on flow and head loss.

Tom_133

Piping

So it doesn't matter the branch size as long as the tee spacing is correct and the pipe size between the runs stay the same as the rest of the primary piping?

Tom_133

Piping

Have I stumped the wall?

Tom_133

Piping

Have I stumped the wall?

Tom_133

Piping

Have I stumped the wall?

Tom_133

Piping

Have I stumped the wall?

Tom_133

Piping

Have I stumped the wall?

Tom_133

Piping

Have I stumped the wall?

Tom_133

Piping

Have I stumped the wall?

Zman

I thought it was answered?

The pipe sizing of the primary and secondary loops should be based on the gpm requirements of the loops.The gpm needed is based on the number of btu's being transported and designed delta t.  The conversion factor link at the top has some good guidelines.



In the system you describe your header is likely sized as a "low head loss" header. This insures even distribution across the zones. I am thinking your 112k boiler will work just fine with 1" piping although some manufacturers will call for 1 1/4" Check your manual to be sure.

Carl

Mark Eatherton

No stumpage here...

As Hydronic Hank (Henry) said, size the branch to the anticipated flow.



Remember also that the Europeans use a 30 to40 degree C differential, which equates to a MUCH lower flow rate than us North Amelicans are used to.



Truth be known, the 20 degree delta T us N.A.ers use is a value that is based on an engineering value to simply make the math easy, In reality, delta T is dictated by a LOT of other variables, all of which vary ;-) I have seen 1 (ONE) system that actually had a 20 degree DT, and it was during a cold, new house start up at design condition. When I went back 24 hours later after all of the mass of the house had been accelerated, the DT dropped to between 7 and 10 degrees F.



Radiant floors (high mass) are a different beast, but still have never seen one attain and maintain their "designed" delta T, even at design conditions.



Size the branches (input and output if you pipe it that way) to the connected load and you will be fine.



Here's some information that is commonly overlooked in P/S piping, that if followed, will lead to a trouble free installation.



ME

Tom_133

Thanks and sorry

Thanks for the comments. I was using my phone and it went crazy posting a lot!!

Tom_133

Just a scenario

ZMan. Don't get hung up on the scenario it was just a quick thought. 1" would probably be just fine. I had a lot of extra 1 1/4 pipe kicking around so I did run into this, I was told by the wholesaler to reduce with 3/4 x 11/4 couplings immediately at the boiler just didn't make sense.



Mark



The diagram is very useful It's great to just look back and use as a rule of thumb!



Thanks guys