Dual Water Heaters - parallel or series

[gmelien]

Had a call from someone that just had there home inspected. There inspector told them

"That the two water heaters could be plumbed in series to improve efficiency. (one tank set low, like 25c, the other set to 56c). He said that they would have been plumbed in series by the builder, and he's wasn't not sure why these ones are in parallel.

Now it my understanding that dual water heaters are supposed to be plumbed in parallel. Am I wrong here?

Thoughts .. opinions, please

[David A. Andersen]

I guess it would all depend if they service two separate circuits or one.

If it is one circuit, they should be in series. If there are two circuits they must remain in parallel.

I had one yesterday where they had one electric water heater and one gas-fired water heater in series. The house was to small to require 100 gallons of hot water. In this set up, they could shut off the gas water heater but not the electric. I recommended that if they did not need 100 gallons of hot water in storage they should have a plumber install a bypass valve so they could use the gas water heater by itself.

With the electric water heater down stream, if you shut it off you get 50 gallons of cold water before the hot water arrives at the faucet.

Turning off the upstream water heater (if they are the same) has no effect on operation, but will save energy loss by not storing unnecessary amounts of hot water.

[Brian E. Kelly]

Originally Posted by gmelien

Had a call from someone that just had there home inspected. There inspector told them

"That the two water heaters could be plumbed in series to improve efficiency. (one tank set low, like 25c, the other set to 56c). He said that they would have been plumbed in series by the builder, and he's wasn't not sure why these ones are in parallel.

Now it my understanding that dual water heaters are supposed to be plumbed in parallel. Am I wrong here?

Thoughts .. opinions, please

Try this Greg.
http://www.inspectapedia.com/plumbin...provement9.htm

[gmelien]

Thank you David and Brian!!

[Nick Gromicko]

Series has an advantage I think. A shower becomes increasingly cooler because the hot water that is used from the water heater is replaced with cold water at a rate faster than the water heater can heat it up. By putting a water heater in between the cold supply and the other hot water heater, you can warm the cold water first so that the final water heater need only heat up already-warm water. This series scenario could potentially be setup where you would never run out of hot water while only paying for the energy to "warm" the water of the upstream tank.. and only paying for the energy to "heat" the already-warm water of the downstream tank. So it isn't quite the cost of keeping two tanks hot like you would have to do if they were parallel.

[Nick Gromicko]

One should note that in predominantly colder climates, it doesn't matter anyway. The energy loss from heating up water on a parallel system that isn't immediately used doesn't disappear. It is lost to the air eventually, which someone is paying to heat anyway.... and besides, tanks are super insulated these days. Turn off your water heater, go on vacation, come home and feel the water... it's pretty warm. Most of the heat loss is suffered in the piping to the fixtures.

[Roy D. Cooke, Sr]

Originally Posted by dandersen

I guess it would all depend if they service two separate circuits or one.

If it is one circuit, they should be in series. If there are two circuits they must remain in parallel.

I had one yesterday where they had one electric water heater and one gas-fired water heater in series. The house was to small to require 100 gallons of hot water. In this set up, they could shut off the gas water heater but not the electric. I recommended that if they did not need 100 gallons of hot water in storage they should have a plumber install a bypass valve so they could use the gas water heater by itself.

With the electric water heater down stream, if you shut it off you get 50 gallons of cold water before the hot water arrives at the faucet.

Turning off the upstream water heater (if they are the same) has no effect on operation, but will save energy loss by not storing unnecessary amounts of hot water.

In some areas where they have ultra lower electric charges in the night use a timer for the middle on the Night .
. This could be a great idea it the electric heater was the upstream and gas down stream .
Nick is correct heat is not lost from water heater for about 8 months when we heat our homes .
Roy

[John Caraway]

If I installed two 50 gallon tanks in parallel, during times of low usage could I not turn off the water to one and just let the pilot burn (or turn off the gas as well). Oh, also turn off the hot water outlet. Then, when I've a houseful of people using three showers I could just reconnect and fire up the second of the heaters.

Any problems with this plan? All thoughts are appreciated.
jc

[Joseph Hagarty, CMI]

There is a community in this area (Malvern Hunt)
The townhomes all had (2) 75 Gallon Gas Fired Water Heaters
- Water Heater 1 / Master Bathroom only.
- Water Heater 2 / Kitchen and remaining Bathrooms & Laundry

Parallel or series makes no difference. It depends upon the design intention.
Obeserve and note accordingly.

[KEVIN WOOD]

You must keep the main water at 120 F if not you will have a chance of building bacteria in the tank. If you plan to use a tank in series this is OK but not parallel.
140 F is recommended in areas critical like Hospitals,Bath areas and Schools.

[Roy D. Cooke, Sr]

Originally Posted by kwood

You must keep the main water at 120 F if not you will have a chance of building bacteria in the tank. If you plan to use a tank in series this is OK but not parallel.
140 F is recommended in areas critical like Hospitals,Bath areas and Schools.

Water heater temp should be at 140°F to stop Bacteria .
Max Tap temp is 120° F

I think that is now Ontario code .
My tap temp is 108°F and tank temp is 140°F

http://antiscald.com/prevention/legi...s/hotwater.php

Roy

[William T. Misegades]

Here is temperature info about the survival of the legionella baterium, which can cause the legion or pontiac fever:

• 70 to 80 °C (158 to 176 °F): Disinfection range
• At 66 °C (151 °F): Legionellae die within 2 minutes
• At 60 °C (140 °F): They die within 32 minutes
• At 55 °C (131 °F): They die within 5 to 6 hours
• Above 50 °C (122 °F): They can survive but do not multiply
• 35 to 46 °C (95 to 115 °F): Ideal growth range
• 20 to 50 °C (68 to 122 °F): Growth range
• Below 20 °C (68 °F): They can survive but are dormant

You'll find pretty much the same info as what Roy posted if you go to this: http://en.wikipedia.org/wiki/Legionellosis

[John Caraway]

Thank you for your comments. I hadn't thought of bacteria. What if the "off" tank were drained during periods of non-use? What problems would you anticipate there?
jc

[Roy D. Cooke, Sr]

Originally Posted by John Caraway

Thank you for your comments. I hadn't thought of bacteria. What if the "off" tank were drained during periods of non-use? What problems would you anticipate there?
jc

That could put the temp about
35 to 46 °C (95 to 115 °F): Ideal growth range
20 to 50 °C (68 to 122 °F): Growth range

If I was going to leave water in the tank then I would add about a pint of Chlorine ... Roy

[John Caraway]

As a non-member I want to thank you all for allowing me to use this forum. I received valuable advice and information.
jc