Q:

What's the effect of introducing bends into a primary-secondary heating loop?

I've been learning about primary-secondary boiler systems for my home, and have landed on a two-boiler system (two apartments), very much like Siegenthaler describes in his illuminating book and here in Radiant and Hydronics.

In order to save space I want to introduce a couple of bends into the primary loop, what's the effect?  The rails are intact but they don't feed directly into the separator as before.  Go/no-go?

In actuality these two boilers are installed along a basement wall with two manifolds extending several feet to the right of the hydraulic separator.  Why not use some of the Z-space?

A:

That is actually a very good system you are proposing. My only reservation is that the cost will be excessive for only 2 apartments or zones. This is a new twist for me on a primary/secondary piping system. I have installed them before but this device makes it so much easier.The amount of elbows and other fittings should not be a problem as long as the total piping friction loss is included in the selection for sizing the primary pump. The use of 2 smaller boilers instead of 1 large boiler will lend itself to better efficiency by allowing for a lead/lag boiler operation and will be much more dependable than 1 boiler for each apartment. 

