Hello, I have an AquaTherm furnace connected with a 40 gallon hot
water heater. When the furnace is on and using the hot water heater,
I get either no or only luke warm water in the house. Does anyone
have any idea what the problem is? Is my hot water heater going, or
is there any adjustment that I can make? Thanks in advance!
Well, it would be good to tell us a bit more about the configuration.
All I can imagine is a sort of strange setup that looks like this based on
| Home |
| Heating |
+----------+ +----------+ | |
| | | |----->| |
|AquaTherm | | Water | +----------+
| | | Tank / |
| |---->| Heater |
| |BTU | |
| | | | +----------+
| | | |----->| |
+----------+ +----------+ | |
^ | Hot Water|
| | Use |----->BTU
| | |
| | |
| | |
BTU or watt hours
The AquaTherm is set up for radiant heating based on circulating hot water.
The outdoor AquaTherm unit is used for heating the water.
There's a hot water heat exchanger and a pump that circulates water from the
firebox and a holding tank.
This *same* tank has been plumbed into the house as the hot water source.
When home heating is needed, the same water is circulated through the floors
in the house.
This removes heat from the water.
So, in really cold weather, the temperature reduction in circulating the
water through the house is noticeable when you draw water for household use.
The whole arrangement seems strange and yet intriguing.
If the water holding tank is also an electric water heater then the
AquaTherm outside wood burner apparently works in tandem with this other
source of energy. Presumably one could save on electricity by circulating
water through the AquaTherm. So that sounds like it could be a good thing.
Now, I don't know if one can expect a domestic water heater to support
radiant heating. They aren't made for that. Of course, there are heaters
that are made for that purpose but I don't know what their outlet
temperatures normally are - maybe the two are compatible. Maybe this is OK.
To make a point:
I have two hot water heaters in series and run the one on the inlet side
when there's going to be high demand for hot water in the house. When
demand is low, the inlet side heater is turned off and just looks like a
piece of pipe. When demand is going to be high, and the inlet heater is
turned on, then the heater on the outlet side looks like a pipe (although it
does add heat) until the inlet side heater runs out of hot water. At that
point, the inlet heater looks like a pipe and the outlet heater operates as
if the inlet heater isn't there (although the inlet heater is adding heat).
On occasion, I run out of hot water when running just one heater.
The point of this description is this: if hot water demands are reasonably
high then the heat stored in the water is easily diminished. There would be
no heat left to heat the house by circulation.
Similarly, if the house is being heated by circulation from the same tank,
there would be much less heat left to allow drawing hot water - particularly
in cold weather. So you would notice that the hot water source for
consumption would have a lower temperature.
A lot has to do with dynamics or transient changes in temperature. But, you
can estimate what will happen by analyzing the average heat requirements:
You can figure out how many BTUs are necessary to heat your house and
convert those to watt hours.
You can figure out how much normal hot water use would use power for your
water heater in watt hours.
You can figure out how much energy it would take to run the hot water heater
100% of the time.
You may be able to estimate how much energy the AquaTherm can deliver.
Presumably the AquaTherm can deliver enough energy to heat the house.
Presumably the water heater can deliver a whole lot more hot water than you
will normally use.
You can calculate how much heat can be taken out of a 100% running water
heater while keeping the water heater on all the time and keeping the water
temperature just at the power shutoff temperature.
You can calculate how much heat the AquaTherm needs to add in order for the
heat delivered to be such that the water temperature stays high.
You can compare the heat the AquaTherm would need to add with the amount of
heat the AquaTherm is capable of.
Water Heater Electric Energy = Wh+We where Wh is power to deliver
AquaTherm thermal energy = At - efficiency factor "ea"
Hot Water use thermal energy input = Wh
Hot Water excess thermal energy input= We (had by leaving the hot water
heater on all the time)
Hot Water thermal energy available to heat the house = We- efficiency factor
Total water heater input energy if left on all the time = We + Wh
Home heating thermal energy load = Ht
Heat available for heating the house while keeping the hot water at high
(At - ea) + (We - eh)
can be set equal to heat needed to heat the house Ht
(At - ea) + (We - eh) = Ht
If Ht is ever higher than the energy available from both sources, then the
water temperature will drop and the house temperature will drop.
This is a steady state analysis based on averages. Actual water temperature
can vary if there's a large draw of hot water from the tank - as an example.
"Is the hot water heater going?" Well, maybe yes and maybe no. Another
analysis would ask, can the AquaTherm take care of everything by itself?
If the left side of the "equation" is larger than the right side, then the
AquaTherm is capable of providing all the energy necessary for heating the
house and for providing hot water - on the average. In that case, the hot
water heater would not have to be turned on or to be working and the loss of
hot water would be perhaps similar to running the hot water until you ran
out - as with a working heater.
So, if the system ever worked in cold weather and if the demands for hot
water haven't gone up in the interim and if it all worked during the last
summer then it could be that the water heater failed some time ago and the
effect is showing up now in the winter.
If there's no acceptable cold weather experience, the system could be
underdesigned for what you're expecting.
First thing: testing the hot water heater should be pretty easy if you shut
off the AquaTherm and pump. Either you get hot water or you don't. Hot
water heater thermostats seem to fail often enough.
Caveat lector. For illustrative purposes only. Could have mistakes or
suggest things that aren't reasonable.....
If the [ommited] diagram is right, that raises another question:
Aren't you supposed to avoid situations where the water system
that drives the houshold heat is sharing/interchanging water
with the potable water supply?
Since there appears to be some confusion on this unit, this post is
meant to clairify:
Aqua Therm is made by First Company, and utilizes a Hot Water Coil fed
from the dwellings hot water heater. This hot water coil is not
"radiant" heat as one respondant hypothicated, but rather incorporated
in a Forced Air Unit. A blower forces air through the hot water coil
and out the supply ducting. A "Taco" pump pumps the water through.
The SAME water that is used for the buildings hot water is used for
space heating. The hot water from the hot water heater is fed through
he coil, and the return feeds back into the cold water supply inlet to
the hot water heater. Obviously there are check valves.
In answer to another posters musings, there is no problem with the
heated water being used double duty for Space Heating and for potable
water supply. Copper pipe is used for building plumbing, and for coil
heating applications. Absolutely nothing harmful is introduced to the
water, it is simply circulating through more pipe. That is all. In an
extremely simplistic example, it is as if we were simply placing a fan
across the hot water pipe coming off David's hot water heater and
making use of its heat to help heat the space. There in lies the rub,
and David's problem: If we force air over the hot pipe, the pipe will
give up some of its heat. The water then is not as hot as it was.
In answer to David's question, there is not a lot he can do. When the
heating unit is in operation, hot water from the water heater is
circulated though the coil. Air is forced over the coil, taking heat
from the water which is then returned to the water heater. The water
heater must cycle to re-heat the water.
David can increase the temperature of his hot water heater. In doing
so, he will increase the heat output of the heater (Aquatherm), and
gain some residual benefit of an increase in the buildings hot water.
He might consider putting scald guards at his fixtures if he ups the
temp too much. This will naturally raise David's utility bills, as the
Heater will run longer.
He can also consider changing the water heater to a larger unit, and
one with the greatest recovery rate he can afford.
Since your hot water is being circulated in a coilIn article
Well, the AquaTherm unit information I gleaned from the web seemed
different. But no matter....
One thing that happens when hot water is circulated might be unexpected.
Nothing happens until you start to seriously draw hot water and then things
change. This situation sounds like that's what's happening.
Example: I had a house with a hot water pump / loop so that hot water would
be more quickly available at the furthest point in the house from the water
heater. We noticed that the water would rather quickly become less than
really hot while taking a shower. If the circulating pump were turned off,
this didn't happen. Why?
The circulating system takes hot water out of the tank as normal and routes
it through the house. The return pipe feeds water into the water heater
cold water inlet side. When there's no hot water being used, this keeps the
water in the pipes hot and doesn't much affect the water heater.
However, when there is hot water being consumed, things change. Instead of
cold water coming in the bottom of the tank and hot water coming out the top
as usual, hot water mixes with cold water coming into the bottom of the
tank. This causes more mixing inside the water tank than normal and quickly
enough the entire tank goes to a lower temperature. This is in contrast to
the normal situation where there being a rather sharp temperature gradient
between cold water at the bottom and hot water at the top.
So, this can be annoying.
There are a couple of solutions:
One can attach a hot water heater thermostat to the water heater inlet pipe
that controls the circulating pump. The idea is to stop circulating if the
inlet water is cold. Something like that....
Another approach is to put two hot water heaters in series and only
circulate water from the heater on the outlet side of the pair. This way,
there's no cold water mixing in the outlet side heater until the inlet side
heater runs out of hot water. The outlet side heater can be small because
it's only other purpose is to circulate hot water - which shouldn't take
much energy if the pipes are insulated. The inlet side heater is not
subject to the kind of mixing that occurs with one heater plus a circulation
Now, if the energy loss in circulation goes up then the outlet side heater
would need to be larger and this wouldn't be such a good solution because
mixing would occur. However, it's probably better than not having two tanks
because really cold water isn't brought into this "mixing tank" right away.
There's no backflow in the loop because the pump is always running. So, I
don't see what a check valve will do. The problem is added mixing in the
heater tank when there's consumption.
I live in a condo and have an AquaTherm furnace and my problem is I only get hot
water if I turn on the heat. It is not much of a problem in the colder weather
but in the summer I have to put the heat on in order to get hot water. I live in
Las Vegas (105 to 110 in the summer)
Thank for any and all help
Hi. A lot of folks especially in the US are not aware of these systems. I have
one in my condo as well in Ohio and faced a similar issue that you described.
It turns out that these systems have two check valves. The valves only allow
water to flow in one direction. If these fail the water starts flowing in
reverse and that is why you get lukewarm water when the system is not on. I
suggest replacing both the check valves to fix this problem. You can pick up
the check vales for around $12/each online and call a plumber to replace them or
do it yourself if you can handle pipe fitting/soldering. If your system was
installed without the check valves, you should install one at the hot water
intake and one at the hot water outlet going back into the hot water heater.
What kind of condo is it? Condo board supposes to take care of things
like that in my case. Our xondo building has one big system for all
units. I don't live in condo. That is rental unit I keep in downtown.
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