I have a multi unit apartment complex.
I've noticed the stack coming off the furnace units, carry a lot of heat to
Can I just disconnect these stacks and my water heater stacks, to harvest
Seems like an awful lot of energy is being directed to the outside.
zzzzzzzzzzzzzzzzzzzzzzzzzzzz splash nibble nibble, maybe even a couple of
In spite of your troll, you bring up a good subject. With many older oil or
gas fired units, as much as 50% of the heat goes up the stack. Industrial
steam boilers often use "economizers" to reclaim a lot of that heat and use
it to pre-heat water being fed into the boiler. Even with efficient home
boilers, the stack temperature has to be about 325 degrees to minimize NOX
Some gas boilers have condensers that do remove some of the heat and thus
the water in the exhaust condenses and must be pumped away.
Electric heat is considered 100% efficient because there is no loss in a
chimney. All the loss is as the power plant and that can be a lot.
If your heating system is more that 20 years old, it may be worth looking
at upgrades. Fuel savings of 24% to 40% is not uncommon. Many states offer
long term low or no interest rate loans if you buy energy star rated heaters
or air conditioners. Depending on fuel prices, the payback for that loan
can come from the savings over the years. Here in CT , that term can be 10
years. Check for your state here http://www.dsireusa.org /
New heating system: $7800
120 payments $65 a month
Fuel @ $3 a gallon, average 850 gallons = $2550
Savings at 30% = $765 a year or $63.75 a month
Right now fuel oil is about $2.40, but a few months back is was $4.50. Next
year, who knows, but now is the time to plan ahead.
The $7800 figure is based on removing my 30 year old boiler with tankless
coil and replacing it with a high efficiency boiler and indirect fired water
heater. The water heater is essentially a storage tank, well insulated,
that holds 40 gallons. First hour draw is about 200 gallons, much higher
than a gas or electric stand alone. I'm getting the System 2000 and it is
being installed tomorrow. Just in time for the coldest weather.
In my municipal location, upgrading to a more efficient furnace requires the
installation of a chimney flue liner to reduce the effective dimension of
the chimney. Less heat, less push against the winter cold air to exhaust
the carbon gases. It really is a 'system' that you cannot mess with one
part and not expect another part to be effective.
The new twist I just heard about, others may already know this: New extra
high efficient furnaces require that any basement air returns be located
something like 72 inches from the furnace. Seems the flue gases are so weak
pushing up against the cold in winter that any furnace cold air return might
draw down (backdraft?) the flue gases into the house air. Someone I know
just had their basement cold air return blocked off.
The unit I'm getting (as do many others) has a fresh air intake for
combustion air. Any movement through the boiler and burner will only suck
in outside air and back out the chimney. I'm not up on the latest furnaces
and heat exchangers so they may differ.
What you are describing is a heat exchanger. These can take many forms but
the idea is always to salvage the heat that would ultimately be lost as
When you are attempting to suck the heat out of combustion exhaust to heat
fresh air you need to consider the possibility that an exhaust leak could be
fatal so some sort of fail safe needs to be designed in to the system to
prevent this. Some designs use fluid that is heated in the exhaust and then
the fresh air is warmed by the fluid flowing through a radiator.
Another thing you need to prevent is preventing the free flow of the exhaust
causing CO to back up on the flue.
The higher fuel prices rise, the shorter the payback on these things are.
Another source of waste heat is shower drains. Some one makes a system
where the hot water flowing down the drain warms the fresh cold water in
route to the water heater.
But are any heat exchangers good and safe, you lower exhaust temp
enough then it can be to cold or acidic for a chimney. You cant buy a
steam boiler of over 83% efficency for a home I cant find one inder
1,100,000 btu, there is a reason I dont know it. You can buy
condensing 93-98% furnaces and HW boilers for a home. Add on exhaust
heat reclaimers have not got good reviews, that I know of. Or the cost
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