Heaters in parallel as backup


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Old 12-14-17, 07:37 PM
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Heaters in parallel as backup

I have 3 water heaters in my basement, 1 for each appartment over 3 floors.
I'm wondering if it's worth connecting the hot water in parallel but with **** off valves only to open the valves if an element fails in the future. This would allow me to provide hot water for the tenants from my heater whilst I replace their broken element.
How would I go about doing this? With 2 heaters, it's easy you just add a shut off/direction between the 2 but what about 3 heaters? Does it mean 6 shut off valves total?
 
  #2  
Old 12-14-17, 10:56 PM
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You could add valving to accomplish this IF you only wanted to use one of the three heaters for the back up fairly easily. But, if I were to do it I think I would only add a "boiler drain" to the outlet piping of the heater to be used as standby and then have a length of 3/4 inch PEX tubing with a hose connection on one end and a female 3/4 inch adapter on the other.

When you needed to make the temporary connection you would get the defective heater out of the way, connect the PEX to the hot water piping where it was disconnected from the heater and the other end to the boiler drain. Honestly, water heaters do not fail often enough to have dedicated cross-connect piping with all the necessary valving.


I worked in a facility that had boilers fired on natural gas with oil back up. Three 25,000 gallon underground tanks and the plant was in use 24/7. When burning oil it was difficult to change tanks without "losing suction" on the fuel pump and getting it going again was something that could take hours under the worst conditions. I had a new manifold built, all welded steel piping and valves to preclude leaks, and when done I could do anything. I could burn from one tank, return to a different tank or even transfer from one tank to another without ever messing with the pump and tank supplying the boilers being fired. It cost about $25k for the installation and sadly the boiler plant was demolished maybe three-four years later.
 
  #3  
Old 12-15-17, 12:03 AM
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Makes sense. I have a spare boiler drain to do this.
Is there any way to connect the 18" flex metal pipe to the boiler drain? I guess not if it's NPT threads.

If I want to work on the hot water outlet of my heater, do I to drain the heater completely or is it enough just to turn the cold inlet off and let out some of the hot water pressure?
I'll get some water coming back out the lines I guess if I don't drain it...
 
  #4  
Old 12-15-17, 12:13 AM
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I suggested the length of PEX pipe because in most cases the flexible connectors would not be long enough. If they are then yes, you could add a regular ball valve with a pipe nipple (3/4 inch size) to mate with the flexible connector.

Remember, it is good practice to replace flexible connectors when replacing a water heater.

Just turning off the power (electric) or turning the gas control to "pilot" and then turning off the cold water feed and draining off a few gallons of water should be sufficient to drain the hot water piping. Remember to purge all the air before turning the power back on or turning the gas valve on.
 
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Old 12-15-17, 02:24 AM
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As a temporary measure, could I just connect everything up with a garden hose and run hot water to the other floor? Having trouble find pex hose couplers for the boiler valve.
 
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Old 12-15-17, 02:33 AM
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Garden hose, absolutely not. Garden hoses are not made to be used with hot water and they may not have the proper materials to use for potable water. A stainless-steel braided washing machine hose would probably be okay.
 
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Old 12-16-17, 04:49 AM
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So, the 3/4 flex pipes used to connect to the top of water heaters. Those will also connect to a 3/4 house connection on a boiler drain?
 

Last edited by qwertyjjj; 12-16-17 at 07:39 AM.
  #8  
Old 12-16-17, 10:43 AM
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No. Boiler drain valves, garden hose valves, washing machine valves ALL have a 3/4 inch HOSE thread. Hose threads are straight and the seal is made with a gasket (washer) whereas PIPE threads are tapered and the seal is made by a combination of the thread sealant and the interference fit of the taper.

The flexible connectors used with water heaters are a kind of cross between hose threads and pipe threads. They have the same form as a pipe thread but without the taper. The seal is made between the gasket in the connector nut and the end of a regular pipe.

If you want to attempt to use the flexible connector to make the temporary cross-connection then forget about the boiler drain and use a regular pipe-thread ball valve. On the outlet use a regular pipe nipple, or better, hexagon pipe nipple made of brass. The water heater flexible connector will fit the brass hexagon nipple perfectly and the hex gives you a place for an adjustable (Crescent) wrench to be used when tightening the nipple into the valve as well as holding the nipple while tightening or loosening the water heater connector.
 
 

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