Drainback system FAQs

panel positioning

If possible, keep panels flush to roof using manufacturer's standard flush mounts to avoid wind loads. Weight load is toward lower portion. Panel performance degrades insignificantly when sun's angle of incidence is less than sixty degrees from normal, because most energy is absorbed via indirect sunlight.

When using channel to extend panel mounts outside of panel footing, extend the top  mounts first as they carry the least amount of physical load.  The lower panel foot mounts carry the most load.

plumbing lines

Be sure to angle plumb feed and return lines from panels as well as the panels and all points inbetween so fluid drains completely when the circulating pump is off.  The system protects against freeze damage by draining the fluid from lines susceptible to freezing.

Insulate piping in the space between walls when piping goes through walls?  Yes, that is best to reduce heat losses and susceptibility to freezing conditions.

higher capacity flowmeter 

"Why are you using a 1-10 gpm solarmeter when the solar panels have a recommended flow rate of 0.5-1.8 gpm?"

The main function of the flowmeter is as a diagnostic tool.  It tells you how well the fluid is circulating.  It may be more difficult to tell between a system circulating well and one with a break in the pipe for example, when a flowmeter with a lower flow rate limit is used.

The pumps generally output higher flow rates as well.  With higher capacity parts, you have the opportunity to add solar panels to the water heating system to generate all the hot water needed all year round* without having to upgrade other parts as well.  The higher capacity can also help to handle installations where piping routes become more complicated than originally expected, or where initial conditions were not fully explored before the system purchase.

Pumps for the open (solar panel) loop of the drainback system tend to be higher capacity than closed-loop circulators, because a circulator in an open-loop has to work a little more to circulate the fluid than a circulator with a similar, but closed loop.

3/4 inch versus 1/2 inch piping

"Is the 3/4 inch return more important for correct operation?"

Drainback systems work in most any climate (at least in the US).  Freeze snap conditions are when it's sunny enough that a system may start warming water, but the temperature drops below freezing quickly such as from a quickly approaching winter storm.

If the system is in a place that freezes, the 3/4inch line provides a little more flexibility to handle freeze-snap conditions, such as where the temperature drops to below freezing temperatures before the controller registers the temperature change and quits pumping fluid to the panels.

Some mountainous and coastal areas are especially prone to fast weather changes. Consider installing a closed-loop water heating system instead of a drainback system where freeze-snaps happen frequently.

* each installed system and water usage must be uniquely considered to determine performance expectations etc.  This is not a claim that any specific system can be upgraded to generate 100% hot water all year.