good afternoon youtube so this is my takagi condensing tankless water heater
and i've got it set right now so the outlet or hot water temperature is 140 fahrenheit which
is as high as it goes currently i'm in the middle of a dishwasher run and the heater just finished
running filling the dishwasher for a rinse cycle and one thing i've just done the other day
is i added a thermometer here this is an indoor outdoor thermometer right now it's about 70
fahrenheit that's the indoor temperature and it's about the same outside it's kind of a smoky
overcast day so it's really not getting very warm but i have this external temperature probe is
mounted up in the exhaust stack it's actually at the very top of the exhaust pipe on the roof and
then i just dropped that beside the three inch pvc venting and ran it down to this thermometer here
so you'll notice the displayed outside temperature is warmer than this 70 fahrenheit it's 81. i'll
turn on the hot water here in the utility sink so there's our incoming water temperature it's
summer here so we get pretty warm water 74 fahrenheit and like i say i'm going up to 140
so this should be 140 right here pretty soon it'll come back there it's coming back down
and then if we look at the gallons per minute 1.3 and what you'll notice is this outside temperature
has started to go up so it was sitting around 80 81 degrees and it's gone up now 10 degrees
and we'll let this run for a while the thermometer doesn't update really fast
there we are 95 and right now with with the temperature rise and this flow rate
the heater is using about 40 000 btus per hour that's about 12 kilowatts and you can
see the temperature now it's going up slower and what i find is it gets up around 100 fahrenheit
and that's as hot as the exhaust temperature gets yeah now the dishwasher just kicked on so
now we're running about 80 000 btus so we've about doubled the output so this will be good we can see
what the temperature goes up to it's right at 100 now 2.7 so the dishwasher is still running
now there we jumped up a bit 104 roughly so that's 40 celsius and like i said we're running well now
the dishwasher just shut off we were running about 80 000 or 24 kilowatts now we're down to about
40 000 or roughly 12 kilowatts and yeah we hit maybe just short of
108 because now it'll probably start coming down i bet yeah see now it's dropped it might have gone
up to 110 fahrenheit it's definitely dropping it's 106. it'll probably even go down from here
running at 40 000 btus runs around 100 fahrenheit maybe a little bit below 40 c up at 80 000 btus
it might hit 110 fahrenheit if you let it run long enough and this heater is rated at
000 so that was running either one-third or two-thirds of the maximum output
now the important thing is this pvc venting is rated for up to 140 fahrenheit
so the manufacturer takagi does specify that you can use pvc venting in fact they supply
pvc adapters with this tankless heater and the the reason they can do that is because this
is a condensing heater there's actually two heat exchangers inside the unit the main
heat exchanger has the gas burner under it and is heating the water to go out the hot water
side but there's a secondary heat exchanger that's taking the exhaust gas that's going up the exhaust
pipe it's taking that hot exhaust gas and it's running the cold water through that heat exchanger
and condensing the water vapor out of the exhaust gas recovering about another 10 percent
energy and reducing the exhaust gas temperatures keeping the exhaust gas below the 140 fahrenheit
operating temperature on the solid core pvc venting now if you have a non-condensing heater
the hot exhaust gas going up the flue is probably well over the boiling point of water and that's
why you have to use a metallic flue it's got to be corrosion resistant because that hot exhaust can
condense and it's mildly acidic so between the two of those you need something like stainless steel
which is much more expensive than the solid core pvc venting i just wanted to show you that that
the temperature on the exhaust stack does not exceed the 140 fahrenheit
in fact they have a temperature sensor inside the unit that monitors the exhaust gas temperature
and if it gets close to that 140 fahrenheit maximum it will shut the heater down on a high
limit so that's one of the misconceptions i've found that people have with tankless heaters
they assume that one tankless heater is pretty much like another tankless heater
so for example someone might have a non-condensing takagi heater in their house
and their heater has stainless steel venting and they assume that all tankless heaters
must have stainless steel venting but there's two factors that influence that one is
if you have a condensing heater you can get by with pvc venting because the condensing heater
keeps the temperature in the exhaust below the temperature rating of the pvc material
but there are some localities like new york city i believe doesn't allow
pvc venting no matter what you have to use metallic venting yeah so you definitely need
to use the solid core pvc you can see this is solid core it's not cellular core drain pipe
now you can probably see a little a few little water droplets on the side of the condensate line
and it was pulling water vapor out of the exhaust and that's how it gets the extra efficiency
so for example this heater is rated at 93 percent efficiency as a condensing
unit if it were non-condensing it would probably be around 80 percent efficient so it's not just an
accident that you can use pvc venting you know the manufacturer had to design in features to
make sure that pvc venting is acceptable you had to choose that as a goal to be able to use pvc
venting and then they had to add features into the heater to make sure that they didn't go above
the temperature rating of that material and they had to design that test that you can see on the
thermometer it works it does what it's supposed to do yeah if you have any other questions about
that go ahead and post up in the comment section below and i'll put some other videos over here
on the left hand side you might be interested in and as always thanks for watching you