I have a multi unit apartment complex.
I've noticed the stack coming off the furnace units, carry a lot of heat to the outside.
Can I just disconnect these stacks and my water heater stacks, to harvest the heat?
Seems like an awful lot of energy is being directed to the outside.
carbon monoxide poisioning, its a killer.
you can upgrade to new high efficency furnaces and water heaters and cut that waste substantially.
who pays for the fuel? you or the tenant?
You might be able to harvest the heat with some sort of heat exchanger that doesn't impede the exhaust. I've seen them on wood-burining stove exhaust stacks.
-Zz
Sure go ahead, harvest away, can you give us your name so everyone can take out a life insurance policy on you.
zzzzzzzzzzzzzzzzzzzzzzzzzzzz splash nibble nibble, maybe even a couple of bites.
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 emissions.
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
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.
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 waste.
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.
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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.
Efficent heating is condensing and no chimney is needed, combustion air is outside air.
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 is excessive
Hi, Ever thought if the stack temp. cools down by removing heat, what would happen to the furnace burner efficiency?
The older funaces needed the hot exhaust, to carry the fumes up the chimney. A stack blower would cool the exhaust, and then the exhaust would remain inside the building.
No, the fumes contain carbon monoxide. And will endanger your residents. You can always replace the furnace with the newer 90% efficient units.
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