outdoor boiler should heat all my domestic HW, right?

 

When I built my house two years ago I got an outdoor wood boiler to
heat it - works great.  I hired a plumber to connect it to my radiant
floor system and through a heat exchanger to heat my domestic hot
water.  However, the hot water heater (propane) kicks on every time we
do a load of wash, take a shower or run the hot water tap. The plumber
says the hot water heater is "topping off" the heat of the water (set
at 115-120) - i.e. the outdoor boiler and exchanger only take it to a
certain point and the hot water heater supplies the rest.

The water leaves the boiler at about 180 degrees and travels less than
100 feet undergroud in an insulated pipe.  MAYBE it loses 20-30 degrees
along the way, and perhaps heating the house takes some more heat away
from the water, but shouldn't there be "enough to go around" for the
hot water heater as well?  I assumed the hot water heater would NEVER
turn on?  Am I an idiot or do I need a new plumber?

 



Barold wrote:


Why is your boiler so far away ? And why *outdoors* ?

Graham

 

Pooh Bear wrote:

Outdoors means that all the wood, dirt, insects, ashes and all
the rest of the mess of a wood burning boiler stay outdoors.
It also means that the boiler can be large without taking up
any valuable space inside the home.

Anthony

 



No pipe insulation I've ever seen is perfect.  Unless you are heating
the house constantly, the first few gallons of water from outside have
probably sat in the pipe long enough and cooled enough (probably to
close to ground temperature) to trick the water heater into powering
on when it is drawn into the tank.  You could install a circulating
pump and keep the run constantly heated all the way to the propane
water heater, you could install a flush valve before the interior WH
and drain the cold water each time before using hot water (time
consuming and wasteful), you could eliminate that propane heater from
the circuit, or you can live with it.  

The cost of constantly pumping water and having it cool in the pipe
run offsets the cost of propane used to  "top off" the hot water, so
you won't save much (if any) money unless you eliminate the gas water
heater entirely.  If you do that, you trade off convenience and
reliability in return for not consuming any gas to heat water or keep
it stored above ambient temperature.  Frankly, I wouldn't obsess over
it, and I probably wouldn't bother to fire up the boiler in summer
unless I did once a month laundry, and fired it up the day before,
then starved it until the next big use of hot water.  This is
obviously a guess based on thin information, and YMMV

 

Thanks Harry.  The pump at the boiler does constantly run, continually
pumping hot water into the house - when the radiant heat circulating
pump or the hot water heater call for heat, the hot water from the
boiler provides the heat...I'm suspicous that the heat exchanger
connected to the hot water heater isn't capable of taking the heat from
the hot water fast or effecient enough to transfer the heat to the
domestic hw.  I assumed the boiler would supply all my domestic hw use.