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Old 08-14-2013, 07:35 PM   #1
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2 50 gallon LP or 1 199K tankless LP


I have a plumbing problem for you.

A house currently has 2 50 gallon LP tanks which service the house as shown in the attached pic.

The home has 2 adults and one baby on the way with the occasional in-law overnight guests.

We are looking into replacing the 2 50 gallon LP tanks with a single Rannai **or** Rheem 199K indoor tankless LP unit. However, doing this will create an additional 45 foot run to the hot water branch at the point where a water heater will be removed.

2 tankless units is too costly, although that would probably be ideal.

Is this advisable? The furthest fixture takes 60 seconds to receive hot water. How much --time-- will be added with an additional 45 feet?

Would adding a hot water recirculator essentially null out any energy savings $$$$ being gained with just one on demand unit servicing the entire house?

Or would a traditional 2 tank setup be the way to go?

We are looking at providing the cheapest route. LP gas here is around $3.10/gallon and currently these two tanks use approximately 30 gallons per month with just 2 people.

Thanks for your input folks.
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Old 08-14-2013, 09:46 PM   #2
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2 50 gallon LP or 1 199K tankless LP


Look at a Navian with a built in circulation pump. Run the recirc line to the farthest fixture and insulate it. Make sure you set it's internal switches to external circulation. I've seen a few and they work well when the switches are correct. A lot of trades men did not read the instructions and I had them fix it during inspection.

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Old 08-15-2013, 11:50 AM   #3
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2 50 gallon LP or 1 199K tankless LP


Quote:
Originally Posted by Ghostmaker View Post
Look at a Navian with a built in circulation pump. Run the recirc line to the farthest fixture and insulate it. Make sure you set it's internal switches to external circulation. I've seen a few and they work well when the switches are correct. A lot of trades men did not read the instructions and I had them fix it during inspection.
Can you explain a little more detail about how a recirc pump works? I didn't know that additional pipe needed to be run for recirc hot water.

Also, how does CPVC hold up to hot water constantly in the pipe? I'm in Florida and CPVC seems to be the norm around here due to hard water.

And most importantly, his reliable are these Navien units? I've read that these break a lot. Would Rannai with an electric 2.5 gallon tank + recirc pump be the way to go instead?

I'm looking to save money here. We don't have a problem with running out of hot water, so the endless hot water sell is not so important.

Should I just buy two new tanks and be done with it? This seems like the most foolproof, maintenance free method to go.

Thoughts?
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Old 08-15-2013, 01:02 PM   #4
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2 50 gallon LP or 1 199K tankless LP


Do you really need 100 gallons of capacity? Gas water heaters recover very quickly. For 2 adults and a baby, it seems that 1 50 gallon gas unit would be enough. Try a test: turn off 1 of the existing water heaters and see if that works for you. If they are plumbed in series make sure you turn of the first tank.
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Old 08-15-2013, 04:50 PM   #5
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2 50 gallon LP or 1 199K tankless LP


They are not plumbed in series. Please see above diagram.

The green and blue colors is a proposed option.

I'm open to all options!

Last edited by noone; 08-15-2013 at 04:55 PM.
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Old 09-10-2013, 05:01 PM   #6
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2 50 gallon LP or 1 199K tankless LP


Wow that is some high cost LP. This is one of those times where there might really be a true ROI on a tankless.

Installing one tankless with a recirc line one it would be ideal. However, it sounds like the cost would be very high to run a recirc line to the furthest demand point since it not new construction.

Rinnai has a high end line works with recirc pumps and I personally think they make a good tankless water heater.

Since cost is the main issue. Can you down size the both tanks to 40 gallon or a 30 gallon for the kitchen and a 40 gallon for the bathrooms? This would save you some install cost and also lower your operating costs.
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Old 09-10-2013, 09:24 PM   #7
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2 50 gallon LP or 1 199K tankless LP


Why would you think that a tankless LP gas unit would be cheaper than an 80 gallon electric that costs much less to operate?

The standby heat loss on a 2.5" thick tank is minimal I think. In other words, I don't think it costs much to keep 80 gallons hot all day.

Regarding a recirc line, I was thinking about putting a pump with thermostat on the furthest fixture which operates only when a light turns on in the bathroom. The kind which you don't need a dedicated recirc line which I assume uses your cold lines to send cold water back through. Is this advisable?
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Old 09-10-2013, 11:23 PM   #8
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2 50 gallon LP or 1 199K tankless LP


I am sorry I am must have missed the 80 gallon electric tank water heater part of the equation.

A single tankless water heater is going to out perform your 2 50 LP tanks, in regards to energy conservation.

Will you be able to ROI the additional cost, most likely not. It typically takes the entire life of the unit (20-25) to ROI a tankless install.

The only proven benefit of a tankless is the endless supply of hot water. All other benefits are very debatable.

Sorry, I can't answer your question about the proposed recirc. I haven't seen that before.

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