I’m in the process of installing a new Marathon water heater, model 8545, which will be coupled to the desuperheater of my geothermal system. The propane water heater that this new unit is replacing has a return line from the far end of the house from one of the bathrooms. This return line allows the hot water to circulate so that this remote bathroom has hot water without waiting 5 minutes for the hot water to reach it. The current configuration that works very well has a ¾ inch copper hot water supply line to this bathroom and tapped into this line at the bathroom end is a ½ line that returns to the hot water tank through a gate-valve and check valve. It attaches to the lower end of the propane hot water tank to a fitting that was supplied for hydronic heating. The Marathon heater does not have this fitting.

Here are my questions,

1. Do I need the check valve in the system?
2. Can the return line be attached to the cold side of the Marathon water heater? It has a dip tube.
3. Some circulation systems tap in to the tank drain valve end, but this is the return point for the hot desuperheater. Not sure if this would work for the return because of this.

Thanks,

Eric D

Eric... Hi.

Let's see if I can help. BRB

You need the check valve in system.

You can tie into cold water inlet to marathon water heater as long as check valve is above connection into heater and pointed in right direction ;) (may need to add expansion tank here between check valve and cold inlet to water heater.. but let's talk connections first).

Some systems do tie into the boiler drain at base of water heater... need to remove boiler drain to do this. I think the marathon has a union type fitting.. so can be done.. but sounds like you have other plans for that tapping?

Cold water connection should work.

BUT for best outcome here... do not hesitate to call the number marathon heaters provided (in instruction sheets) to ask any question regarding their heater.

THEY have supplemental specification sheets available that will tell you exactly how marathon heaters wants you to pipe this AND KEEP their warranty in effect.

Check out Marathon Water Heaters for numbers/information... get back to us.

Is your recirc. Line insulated? Let me know your thoughts... Mark

Quote:

---

Originally Posted by massplumber2008

You need the check valve in system.

Is your recirc. line insulated?? Let me know your thoughts...Mark

---

Hi Mark,

Thanks for your input. Yes, the recirc line is insulated. It has worked well for the last 9+ years. I have found that every bit of air needs to be out of the line for it to work properly. When I have opened the water lines for changes or what have you, the return will stop working until I bleed the air out a few times. Thanks for pointing out the Marathon website. I've been there a number of times even before buying my unit.

Oh, I had the model number wrong in my first post. It is a MR85245B. The unit is about 124 lbs empty. Not to bad for 85 gallon tank. I managed to get it down my basement with a two wheel hand truck. I'll let you know how it works with the new unit once I complete the installation. With a little luck that should be tomorrow.

Regards,

Eric D

This weekend I completed the installation of my new Marathon water heater and connection to my geothermal desuperheater. The MR85245 B unit is assume. After bleeding off all the air in the tank, I turned on the power. There was hot water in less then an hour. The desuperheater works better then I expected, water in temperature 90° and out of the desuperheater 165° F. So far I would recommend the Marathon line of water heaters. The insulation of this tank is amazing. The only place you can feel any warmth of the water in the Marathon tank is the outlet nipple. Two thumbs up!

Eric D

Glad to hear it! Nice system this marathon heater... think we will be hearing about it a lot more. Watch for the need to add that expansion tank... you never know.. ;)

And thanks for popping in to answer that pump question... I am still waiting for the answer to your question and HKSTROUDs. Just hope he comes back for answers! Good night... Mark

Mark,

Like you I was a little concern if I would need a dedicated water heater expansion tank or not with this 85 gallon unit and the desuperheater system. I've been monitoring pressures and temperatures. Late yesterday evening the desuperheater circuit shut its circulating pump down once the inlet side got to 140° F and the pressures all look fine. What I still need to figure out is if I need to lower the set temperature of the lower water heater element. I've been told it is normal to reduce its set point with the desuperheater. I wish there was a simple indicator light at each heating element that would tell if they are on or not. I'm going to call Marathon today and see what they suggest on the set points.

Thanks again for your input!

Eric D