Dual Pool heaters ... how to plumb?

Feb 19, 2016
17
New Hampton
#1
I have a heat pump currently installed and I'm adding a gas heater....

what is the best way to plumb this ? In series with heat pump first then gas heater?

I've read that it's better to have water flowing through both then having water sit in one if not being used for a couple weeks etc.

Thoughts?

thanks in advance I appreciate your time!
 

Bama Rambler

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2009
22,810
SouthWest Alabama
#2
If you're going to use them concurrently (i.e. use gas to heat the pool and then HP to maintain the temp) then plumbing them in series as you describe is the proper way to do it. If you're never going to use them at the same time then plumbing them parallel to each other will have less head loss, but will leave one full of water unless you also provide a way of draining them independently, which I would recommend. As long as your water is balanced it won't hurt the heaters to sit full of water for a long time.
 
Jan 4, 2013
24
Middletown, DE
#3
In parallel makes the most sense to me. This allows you to use them simultaneously for the largest temp gain, but I wouldn't use both simultaneously to simply maintain temps as only one heater's thermostat would inevitably read lower and do the cycling and that heater may not be the one you prefer for that job. The benefit I see to parallel also is that you can have (treated) water running through both all the time keeping the internals balanced and wearing at the same rate. I would still plumb to be able to bypass and drain either independently as well as an entire heater bypass loop, but that's just me. Parallel also will reduce head losses vs series as Bama mentioned above.

Maybe if you gave us a little more information as to what your goals are we can better help.
 
Feb 19, 2016
17
New Hampton
#4
thanks for the replies...

My ultimate goal is to use both heaters efficiently when possible and also gain maximum heating capacity from both when a quick rise in temperature is desired.

I will be controlling both heaters with a hayward omnilogic system which will allow me to set the heatpump to run only if the outside air temp is above a certain setpoint otherwise fall back to the gas heater. Additionally through the omnilogic I believe I can also set heating to use the heat pump as the primary source and if the system doesn't see X temperature rise in X amount of time then to call on the gas heater as well for additionally heating capacity.

My concern is more so on the plumbing side as to how to be the most efficient regarding getting the maximum efficiency from the gas heater.
I am running a hayward ecostar variable speed pump that is also controlled through the omnilogic system.

I'm not sure if just plumbing both heaters in series is the way to go or to automate a series/parallel loop for the heaters with automated valves... this would ultimately leave water sitting in either heat exchanger for longer periods of time which i've read mixed things about doing.

Additionally I believe the sweet spot for each heater is approximately 55-60 GPM through each heater, if I run a series/parallel setup I would essentially need to be pumping significantly more water to establish that flow rate through each heater, versus just having them in series I could keep the variable speed pump throttled to achieve the 60 gpm.

Curious to everyone's thoughts on the best way of doing all this.

thanks again for your time it's greatly appreciated.
 

Bama Rambler

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2009
22,810
SouthWest Alabama
#5
Given your operating parameters, I'd plumb them in parallel with a pair of automated 3-way valves to select which heater gets the flow. The omnilogic should be able to operate the valves when it selects the heater.
 
Jan 4, 2013
24
Middletown, DE
#6
^^^ What he said.

I didn't know Ominlogic was that flexible. I've been considering automation for the past couple of years and have done some research but not everything is easily found. It seemed to me to really know the differences between brands and even different lines within the same brands, I would have to read the manuals! That's no fun and a lot of memory. One specific question I have and maybe you could answer since you seem very familiar with the Omnilogic is for the control of automated valves. Does Ominlogic or any other automation product offer precision control (incremental) of the valves as opposed to only open/closed? As far as I know only 100% open/closed is offered in the Pentair lines. Any ideas? Sorry for the brief off topic.
 

PoolGate

Gold Supporter
TFP Guide
Jun 7, 2017
2,436
Damascus, MD
#8
Alright so the stagnant water sitting in the exchanger I shouldn't be concerned with even if it's for an extended time?
For my water features that I don't use much, I have 10 minutes in the morning that I have my automation system open up the valve to them to keep the water fresh. If I was you I would do the same thing with yours (providing you have automated valve).
 
Feb 19, 2016
17
New Hampton
#9
good idea poolgate...

alright so i'm thinking i'm going to plumb them in parrallel with an automated valve on each input side of each heater. There is nothing wrong with leaving pressure on the return side correct?

onlyjeeps... i'm not familiar with an incremental style valve. i'm sure there's some options out there but I haven't dealt with one... depending on the application you're looking to use it for you could potentially use a variable speed pump etc
 

PoolGate

Gold Supporter
TFP Guide
Jun 7, 2017
2,436
Damascus, MD
#10
good idea poolgate...

alright so i'm thinking i'm going to plumb them in parrallel with an automated valve on each input side of each heater. There is nothing wrong with leaving pressure on the return side correct?

onlyjeeps... i'm not familiar with an incremental style valve. i'm sure there's some options out there but I haven't dealt with one... depending on the application you're looking to use it for you could potentially use a variable speed pump etc
Increasing return pressure is ok as long as you don't totally stop it. The thing to keep in mind is that most automatic valves are not variable stop points. They are activated and then go stop to stop. You could automate a 3 way valve to switch between 1 heater or the other heater but not both heaters at the same time (unless you have both off or both on). So you have 1 heater plumbed always on and you'd put the automatic valve between that and the other heater to bypass it or turn it on as desired. This is exactly how my water features are activated. I can shut off both with an automated valve. Once that valve is on, I can turn on my rock waterfall or not. I can never have only the rock waterfall though. So both off, sheer only, or sheer and rock. It disappoints me that I cannot have rock only. I could do that if I remove the valve motor and hand activate it. And of course there are many other ways to plumb.
 
#11
so in my diagram below I have the heaters in parrallel with each other.... on the "from filter side" i'm going to put a 2 way automated valve on each input to each heater. I'm going to leave the output plumbed directly to T fittings that connect back to the pool return side. Does anyone see any issues with this? This will allow me to run either heater independently or both together at the same time while feeding cold water to each heater. Or I can have both valves closed and add a bypass valve plumbed to the return that opens if neither heater is active to bypass both heaters entirely.



dualheater.jpg
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
3,952
FL
#12
From a "in the field" perspective, parallel installation uses heaters that are identical in BTU. Heat pump first and then the gas heater.
 

PoolguyinCT

In The Industry
Jul 21, 2014
2,667
Connecticut
#14
so in my diagram below I have the heaters in parrallel with each other.... on the "from filter side" i'm going to put a 2 way automated valve on each input to each heater. I'm going to leave the output plumbed directly to T fittings that connect back to the pool return side. Does anyone see any issues with this? This will allow me to run either heater independently or both together at the same time while feeding cold water to each heater. Or I can have both valves closed and add a bypass valve plumbed to the return that opens if neither heater is active to bypass both heaters entirely.



View attachment 75778
It would take 2 actuators per unit, on feed & discharge in an H shape. Valves connected by pipe to make the “ H “& rotors stops adjusted
Unlikely have the controls to carry 4 more actuators. & it’s not really practical.

There no reason not to have water flow through both units.

If you have controls, one can use the “solar” switch & other “heater” switch on the panel.

For practicality, I’m with ps303 on this one, I’ll scan my photos - if I have a pic of a tandem install I’ll post it.
 

ps0303

TFP Expert
In The Industry
Jul 6, 2011
3,952
FL
#15
Here is the setup I would suggest. I also removed the extra thermometer you had after the gas heater. You really only need one.

HEATER SET UP.jpg
 
#17
Thanks guys.... I'm thinking I'm going to dumb down my initial parallel and valve idea and just plumb them in series as you have it... install will be so much simpler and less to go wrong down the road with valves.

If I plumb them in series as in the diagram do you see any negative effects from running them both at the same time if I'm trying to get the fastest heat rise I can?
 

PoolGate

Gold Supporter
TFP Guide
Jun 7, 2017
2,436
Damascus, MD
#18
Thanks guys.... I'm thinking I'm going to dumb down my initial parallel and valve idea and just plumb them in series as you have it... install will be so much simpler and less to go wrong down the road with valves.

If I plumb them in series as in the diagram do you see any negative effects from running them both at the same time if I'm trying to get the fastest heat rise I can?
None at all but I think it will be a waste of power for the heat pump to run at the same time. Heat pumps do not create a lot of heat fast. The minuscule amount they will add as a pre-heater to the gas heater IMO is a waste of money and adds wear and tear to the heat pump. Heat it to temp with the gas then switch on the heat pump to maintain that heat.
 

PoolguyinCT

In The Industry
Jul 21, 2014
2,667
Connecticut
#19
None at all but I think it will be a waste of power for the heat pump to run at the same time. Heat pumps do not create a lot of heat fast. The minuscule amount they will add as a pre-heater to the gas heater IMO is a waste of money and adds wear and tear to the heat pump. Heat it to temp with the gas then switch on the heat pump to maintain that heat.
Bingo!!