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Phil, Mechanical Engineer.
Category: Plumbing
Satisfied Customers: 8705
Experience:  Retired mech. contractor, shop owner, 51 yrs experience.
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I have a Rheem loline 260 ltr solar gas boosted unit. What

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I have a Rheem loline 260 ltr solar gas boosted unit. What would be the effect on its efficiency if the hot water and cold water pipes on the solar panels were reversed

Welcome to Just Answer!

Because of the way air can be trapped in the system if you reverse the hot and cold connections to the panel it can stop the water flow... the panels can then overheat.

Give me some details on what problems you are experiencing, we can go from there without any time limit.


Customer: replied 4 years ago.

Thank you for your answer.


With the hot water being taken from the bottom of the unit and the cold going into the top – I am concerned as to whether this would make the unit less efficient and more reliant upon the gas boost ie would this increase my gas bill by any appreciable amount. When I turn the boost off, there seems to be not much hot water even in summer.

Hello again,


See page 35 piping diagram. If you reverse the tank connections so that the hot water comes out the bottom and the cold water supply goes in the top, the system will be less efficient by 30% to 50% or so, depending on solar intensity at the time... the lower the solar intensity the less efficient the system will be hooked up that way.

The natural flow through the solar collector is from the bottom up... by connecting the cold water so that it enters the solar panel at the top turbulence and uneven flow through the solar collector occurs. That reduces efficiency.

Let me know if that helps or not, we continue as needed.
If you choose to rate my work so far *positively, I can hold the question for any follow up needed,


Customer: replied 4 years ago.

Thanks Phil,


Does this reduction of 30 - 50% in efficiency directly relate to a similar percentage increase in gas usage



Hello again, yes you will use more gas, but we don't know how much more because of climate and other variables...30 to 50% is a fair guess however.... it depends on how much hot water you use in excess of what is collected by solar... if you used just 20 gallons a day, there would be days when you would use no gas...

if you used 100 gallons a day you would use a lot more gas. That would vary seasonally as well.

Is there some reason you are not going to change the piping back to match the diagram on page 4.

Please don't forget to rate my answer positively when you are happy with it... lacking that we keep going until you have what you need.


Hello again, there some issues involving check valves, Can you tell me if you have been running this system hooked up in reverse or are you considering hooking it up in reverse but have not done so yet?

I need that detail, to advise you beyond just the efficiency issues you mentioned.

Customer: replied 4 years ago.

Thanks Phil

We engaged a plumber in March this year to check on the HWS.

He replaced a faulty pump and also reported that the hot and cold pipes were incorrectly installed when the initial installation of the panels was carried out.( that was when the house was built in late 2007)


The pipework was repiped to ensure correct direction of flow.


What I am attempting to establish is what effect the faulty workmanship would have had on the unit and the gas bill.

Hello again, thanks for the background information..

You can compare your gas bills on a monthly basis before and after the piping was corrected to get the added gas usage and cost figures.....those would likely be quite accurate.

Proving to a court etc, that you had not changed your hot water use... would be a much more difficult matter.. see my previous post on that topic. If you consistently used less hot water than the solar was able to provide for instance, there would be no increase in the gas bill even though the system was less efficient when hooked up backwards.

If you have a gas furnace and as stove, that would dilute the figures... Typically the money spent on domestic hot water heating is a very small fraction of the total use... often just $20 or $30 a month depending on the size of the family,


Customer: replied 4 years ago.

Thanks for the info Phil and the promptness of your replies.

You are welcome! The company pays me a percentage of your deposit if you rate my work for *positively! They don't pay me otherwise I

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