I live in a typical Boston triple decker. We have oil and radiators
for heating. I don't think we have any kind of hot water tank, the
only tank I see in the basement is the oil tank. The problem is that
when the radiators are very hot to the touch I know I'm in for a cold
shower, but if the radiators are warm to cool then the shower is fine.
Is there some kind of valve that could be adjusted so that every bit
of hot water is not pushed out to the radiators, to save some for
If you have hot water heat, your oil burner has an aquastat. The "upper limit"
cycles the oil burner on and off, just like a thermostat to keep the water
inside at the set temperature.
There should also be a "lower limit" or "circulator" setting, which is either
not functioning properly or set too low, or maybe you have steam heat?
The lower limit cycles the heat circulator pump(s) on (when the boiler temp is
high enough) and off (when the boiler temp is too low.) This is so that the
circulators aren't pushing cold water around your radiators and to decrease the
load on the boiler during periods of domestic hot water need.
When we moved into our house we had the same problem. The service person
raised the water heater temp range from (120 min-140 max) to (160 min-180
max.) Now, although you need to push the lever 3/4 of the way to hot, we
get a decent shower when the heat is on.
It sounds like you've got a hot water coil in your boiler to supply
domestic hot water. Part of that system is a tempering valve, which will
mix hot water with cold water, to keep the hot water to a non-scalding
temperature. As your boiler temperature drops when the radiators are
operating, less cold water is added by the tempering valve, keeping the
domestic hot water temperature constant (more or less).
Over time the valve tends to freeze up, sticking in one position. If
it's stuck where it's adding a lot of cold water, you'll only have
sufficiently hot water when the boiler temperature is near its maximum.
There should be an adjustment knob on the tempering valve (it should be
located near where the water coil enters the boiler) to let you make the
water hotter or colder. See if you can simply move it to hotter. My
guess though, is that it's frozen in place over time.
It's also possible the previous two posters are correct, BTW.
You probably have large radiators that hold a lot of water. When the
circulator pump goes on, it pumps the heated water from the boiler to the
radiators and brings down lots of lukewarm water from the radiators. This
reduces the temperature of the water in the boiler and it takes a while for
it to return to the proper temperature. This is the same water that passes
through a coil (heat exchanger) to provide the heat to warm your hot water.
If it's not hot enough, your hot water won't be either. If adjusting the
aquastat as others recommended, does not help, try turning down the
thermostat before you take your shower. This will turn off the circulator
pump and allow the water in the boiler to heat more quickly. Turn it back
up when you finish your shower.
To permanently fix the problem (if you own the house) you probably need to
add a gas fired water heater in series with the output of coil. During the
heating season this will allow you feed warm (or even hot) water into the
heater (truly a hot water heater <g>) so that it will not take much gas to
provide you with plenty of hot water at all times. And in the summer, it
will provide you with hot water without having to run the boiler when it is
not need for heat.
"Seth Goodman" <seth email@example.com> wrote in message
My service tech offered the solution of a small storage tank and
recirculator in line with the furnace to store a reserve of water for heavy
use periods (50 gallons) I have an oil fired furnace with coil (no tank)
Yes that would work too, but it is probably no cheaper than a new water
heater and does not have the advantage of being able to shut down the boiler
in the non-heating season. OTOH, it most likely would have a longer useful
life than a water heater.
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