DIYbanter - View Single Post - Tankless in series with Traditional Water Heater?

Eric

wrote:

I have a 50Gal hot water heater under my house serving 2 bathrooms and
four people. I am looking for a safe way to prolong the availability of
hot water when two or three people take a shower in a row. I was
thinking about putting an inline water heater before the 50gal tank
heater. I don't want to buy a big inline heater, as it's just going to
be for stretching out the hot water available during a 40 minute
period. The problem I see is the max flow through the inline unit will
be too small. Do they make inline units that will flow at arbitrary
rates, and just heat the water less when flowing fast? This would be
ideal for me. Otherwise, could I split the flow (in parallel) going
into the tank water heater: half through the inline unit, and 2) half
through some restrictor valve to even the bias?
If it were me I'd reverse the connection you propose, incoming cold to HW
tank, then output that to the tankless. Set the HW tank temp down very low
(start at somewhere below 90F, adjust to suit as you get experience with it)
so the Tankless has to manage a smaller temperature rise. Then you'd pretty
much have unlimited hot water.
Here's what i did. I got an old HW tank, stripped off the shell and painted
the tank flat black with rustoleum [several coats]. It sits on a small
concrete pad i made outside my garage on south side. Then I plumbed it in
series with the HW tank, the incoming cold goes to the black tank, sun
heats it a bit (its outside in the sun) and the mildly warm water feeds
into the cold inlet on the HW tank in the garage. This reduces the work
load of the water heater and lowers my bill. The outside tank has a
temperature relief as does the inside tank for safety. The inside tank is
blanket wrapped to also improve its efficiency. My next addition will be to
build a plexiglass box around the outside tank and, being up here in NW US
where winters are generally above freezing, that should extend the portion
of each year i can use it by quite a bit.
Eric

Of course its bypassed and drained in the winter but in summer it makes a
significant contribution to heating my water.