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Hot water heating

user-471779 | Posted in General Questions on

Need some advice on my domestic hot water plan…
very long and narrow ranch house… well water. good pressure..

Master side of the house has Master bath. (with soaker tub), 3 other full baths and a half bath…. all fairly close to each other…

kithcen side is very far away.. (75-100 feet away) … has a full bath , half bath, and kitchen sink…and a washing machine.

On Master side i am planning on a large heat pump water heater( i have a good utility room for it) attached to a manifold with 1/2 lines to showers, 3/8 lines to sinks and toilet.
was also planning on running 3/4 directly to soaker tub.

On kitchen side… I was going to install a Marathon electric tank fed from the heat pump water heater on the master side……( so at least it is getting pre heated?).. with another manifold to feed that side.. with very short runs to the fixtures…thus having the hot water from the marathon quickly reach the fixtures.

1. I am trying to solve the long distance between the two areas of the house… does this sound like a good plan? Or should I use some sort of recirculating method instead between the two manifolds? we just dont want to wait forever for hot water at the kitchen sink…

2. what is the best heat pump water heater out there?

3. I really like the idea of two manifolds… I like the concept of no connections in the walls… Does 3/8″ make sense to the sinks and toilets, and 1/2″ to the showers?

I do have gas available… but for some reason i dont want to use it… except for my range, grill, and a fireplace… am going with a whole house mitsubishi eletric hvac system without gas as well.

anyway… thanks for the advice in advance…

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  1. GBA Editor
    Martin Holladay | | #1

    Considering your goals, your plan makes sense. Choose the smallest available Marathon heater (model MR30245 has a capacity of 30 gallons).

    When it comes to heat-pump water heaters, those manufactured by Stiebel Eltron have a good reputation.

    Since you are going all-electric, don't forget to install a PV array on your roof or in your yard (assuming that your local utility offers favorable net-metering agreements).

  2. user-471779 | | #2

    Thank you Martin,
    I guess I haven't even thought of PV, but I have gone so far everywhere else, is there a good article that explains the basics of PV to start learning about it?.

    Also, Since the largest line i will have coming off of the kitchen side manifold is 1/2... can I just run a 1/2 line to the small marathon that feeds that manifold? In essence it will hold less water that will be cooling down and take a shorter time from the heat pump water heater?

  3. Reid Baldwin | | #3

    Why are you running hot water to your toilets?

  4. GBA Editor
    Martin Holladay | | #4

    I'm going to assume that you will be running only cold water to your toilets.

    You might as well run 1/2" tubing to your toilets -- they'll fill faster that way. (The issues surrounding "waiting for hot water to arrive" don't apply to toilets.)

    Most people are satisfied with the performance of 3/8" lines to lavatories -- but check with your local code inspector to see if that approach is legal in your jurisdiction. The longer the 3/8" line, and the more elbows, the less satisfying the flow rate... so this approach works best for shorter runs with few fittings.

    Here are a couple of links to articles on PV systems:

    An Introduction to Photovoltaic Systems

    Making Room for a PV Array

  5. user-471779 | | #5

    ok, so all home runs from the 1/2 to toilets, 1/2 to showers, 1/2 to cold side faucet, I guess the only decision if I am getting super ocd is whether or not to run 3/8 hot or 1/2 hot to sinks hot side. I guess i am obsessing over the fact that 3/8 will get the hot water there faster because there is less in the line... how can I calculate whether or not there will be enough pressure for the handsink with the 3/8?

  6. GBA Editor
    Martin Holladay | | #6

    For guidelines on 3/8-inch tubing, read what Gary Klein has to say: Inefficient Hot Water Piping Layouts Waste Hot Water.

  7. PaKettle | | #7

    For the main cold runs I prefer 1 inch to both manifolds and the main hot water heater. The extra cost is almost trivial and will eliminate the potential for pressure/volume issues.

    The soaker tub uses a lot of water and generally you want it to fill fast so 3/4 lines are easily justified for both hot and cold.(check your faucets flow rate, 5 gpm minimum)

    3/8 is plenty for hand washing but if you want to fill a sink in a hurry like the kitchen then 1/2 would be more usable.

    There is also the hybrid approach where a single line is run to small manifolds in each area/room instead of having a single manifold with a hundred lines running everywhere.

    You could use a small tankless heater(s) on the kitchen side to handle everything but the tub and showers which could be fed by a separate hot 1/2 inch run from the master.

    Pulling hot water from your heatpump on the master side would not be a good idea except on high volume usages. The water will never reach the second heater and end up being at room temperature resulting in a lot of wasted heat.

  8. user-471779 | | #8

    so, an electric tankless heater for the kitchen sink, dishwasher, washing machine, guest sink, guest bedroom sink.... you think this is a better idea than a small marathon? If so can you recommend a model of electric tankless?

  9. GBA Editor
    Martin Holladay | | #9

    The main disadvantage of point-of-use electric water heaters (or whole-house tankless electric water heaters) is that these appliances have huge amp-draw requirements. You'll probably need 200-amp electrical service to make this possible. Before you decide you want to do this, talk to an electrician.

    Tank-style heaters have lower amperage requirements.

    If you decide to use point-of-use electric heaters -- and there are reasons you might want to -- Stiebel Eltron is a reputable manufacturer.

    For more information on this topic, see Point-of-Use Electric Tankless Water Heaters.

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