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Why
would I need an energy-recovery ventilator like RenewAire?
As
houses become more and more airtight, it will become more and
more common to see energy-recovery ventilators in homes. Air-tightness
follows from the use of improved building practices and products,
like air barriers, better seals on windows and doors, panelized
construction, air-sealing procedures, and sealed-combustion
furnaces and water heaters.
People
like the benefits of air-tightness in their homes, including
improved energy efficiency, fewer uncomfortable drafts, and
the exclusion of noise and dust from the outside. What is lost,
however, is the natural infiltration that used to carry away
the indoor pollutants: carbon dioxide, formaldehyde, cool-weather
moisture, cooking odors, and other gases coming from building
materials and cleaning compounds.
In
old houses, natural infiltration was so effective in removing
these pollutants that often, more water was carried away than
was generated in the home by the breathing, washing, and cooking
of the occupants (thus the need for additional humidification
in older homes). Nowadays, that water isn't removed from the
new, tighter houses, unless a ventilation system is in use,
so windows can be damaged by the moisture build-up. With "run-away
humidity" insulation loses its effectiveness, and in severe
cases, structural damage can occur.
Even
though we do not know everything about pollutants in homes yet,
there is real concern. Formaldehyde originating in various board
products and insulations caused significant problems in the
building products industry. Changes in product formulations
to try and reduce the amount of formaldehyde because of possible
health concerns have only been partially successful. There are
other pollutants that may be of concern. A common one is carbon
dioxide, which in excess concentrations can cause lethargy and
lack of alertness. We all generate carbon dioxide by breathing,
but it can be very effectively controlled by air-to-air heat
exchangers. A ventilation system provides better indoor air
quality.
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How
does the system work?
A
RenewAire ventilation system exhausts stale air from the house.
At the same time it draws in fresh outside air. Within RenewAire's
energy-exchange core, heat and moisture is transferred from
one air stream to the other - but each air stream is kept physically
separate. The fresh air stream is automatically preheated, or
pre-cooled, depending on the season.
The
result is that the pollutants in the inside air are regularly
exhausted to the outside - but the winter-time heat (or summer-time
coolness) in the household air is largely recovered, so that
you can afford to ventilate without a large impact on your heating
or cooling cost.
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What
will RenewAire do for me?
Most
importantly, it will give you cleaner air to breathe, letting
you and your family feel better and healthier. It will do so
in the most consistent, controlled, safe, and energy-efficient
manner possible.
In
winter, the RenewAire system will control damaging high humidity
in the home.
RenewAire
also controls the difference in air pressure between the inside
and the outside of the home. It reduces the amount of cold air
entering the house around doors, windows, and other leaks, all
of which can give you a cold, uncomfortable feeling. Now all
the ventilation air brought into your home is directed into
your heating ductwork or to a central location. At the same
time, that ventilation air is made to recapture most of the
energy that would otherwise be lost through ordinary ventilation.
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Is
RenewAire an air filter?
Filters
work by pulling fine, air-borne particles out of an air stream.
Some filters are very good at removing particles from air, but
filters can't pull gas pollutants out of the air.
Air-to-air
heat exchangers control indoor gas pollutants by bringing in
outside air. The filters inside RenewAire are there strictly
to prevent fouling of the RenewAire core.
Even
the best filter, if installed as part of a RenewAire system,
can only screen out the particles coming from outside. In most
installations, RenewAire systems bring in only small amounts
of air-borne particles. The other sources for dust, pollen,
and other air-born particles (many inside the home) are much
more significant.
People
who are concerned about removing fine particles from the air
in their homes need to use high-efficiency (HEPA) filters on
their furnaces, which treat a high volume of household air.
That is the only way to effectively deal with particles in the
air inside the home.
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Is
RenewAire certified by an independent testing agency?
RenewAire
products are currently the only residential products to carry
certification from both HVI and ARI. The Home Ventilating Institute
HVI has tested and certifies the performance of residential
units for approximately 10 years. HVI uses the Canadian CSA
439 test protocol. This tests for airflow, temperature and total
(heat and humidity) efficiency, cross leakage, and low temperature
(-13° F) performance. RenewAire not only passed these tests
to achieve certification, but also rates among the highest performing
produces in all categories. In January of 2001, certified test
results from ARI-1060 were first published.
RenewAire
uses one of the largest energy-recovery cores in the industry,
relative to airflow rate. And our plate spacing is very close
(the plates are the dividers that separate the air passages
and transfer energy from exhaust air to fresh air). That means
we can pack a lot of exchange area into a small volume. Most
other manufacturers use smaller elements with larger plate spacing.
This is a major reason why RenewAire efficiency is among the
highest tested.
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Are
RenewAire products UL-listed?
In
1986 a RenewAire unit was the first HRV to be tested under UL's
special category for Ducted Heat Recovery Ventilators. Our products
continue to be UL Listed. Our factory is regularly inspected
by UL, as part of an ongoing safety and quality inspection program.
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What kind of warranty protection is available from RenewAire?
RenewAire
provides a ten-year warranty on the core. All other components
carry a two-year warranty.
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Why
is RenewAire the best available way to ventilate?
While
there are other ways to provide controlled ventilation in your
home, thus reducing gaseous indoor air pollution, here are four
reasons why RenewAire is the BEST:
- Balanced
Ventilation is safest for you and your home - can't back-draft
chimney-vented appliances, and won't pull or push moist air
into your home's insulated walls.
- Enthalpy
Exchange means RenewAire can recover heating (or cooling)
energy efficiently, without interruption, winter or summer
- core stays dry, with no need to compromise heat recovery
for defrosting.
- Simple
design means easy installation and reliable operation.
- Time-tested,
documented performance. We have been manufacturing energy-recovery
ventilators in Madison, Wisconsin since 1983. Tens of thousands
of RenewAire units are installed throughout the United States,
providing reliable, efficient service.
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If
RenewAire recovers moisture, can I still get rid of excess winter
humidity?
RenewAire
is effective at controlling excess winter humidity in tight
houses because it doesn't recover all of the moisture from the
exhaust air. The RenewAire core is designed to recover less
moisture than heat, so plenty of excess moisture is still blown
out of the house. And because cold-weather air is very dry,
the long-term effect is making the house dryer.
Excess
winter humidity is one of the top problems people solve with
RenewAire. Studies show that enthalpic-transfer ventilators
like RenewAire, when operated at the ventilation rates recommended
to control poor indoor air quality, have plenty of moisture-removal
capability in cold climates.
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What
does moisture transfer do for me in the summer?
Plenty!
When ventilating in the summer, the challenge is to keep the
excess moisture in the outside air from coming in. That is the
opposite of the situation in the winter, when ventilation is
used to get rid of excess moisture generated inside the house.
If
the air inside the home is dryer than the outside air - when
air-conditioning, for example - the RenewAire core transfers
much of the excess moisture from the incoming ventilation air
to the outgoing exhaust air. This reduces both the excess heat
content and the excess moisture content of summer ventilation
air by about two-thirds, overall. Without the moisture transfer
feature, the moisture content would rarely be reduced at all.
Since
dehumidification is a major part of the work an air-conditioning
system does, this excess moisture reduction feature is critical
in maintaining the energy efficiency of summer-time ventilation.
In typical hot weather, humidity may represent 60% of the energy
that needs to be removed from outside air. Other products that
can't control this humidity perform very poorly in the summer,
compared to RenewAire.
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Will
RenewAire Units dehumidify my house in the summer if I'm not
using air-conditioning?
The
dehumidification effect that RenewAire provides in the winter
is absent or very minor in the summer. In a house without air-conditioning,
the water content of the air inside and outside of the house
is virtually the same, so air exchange won't provide any humidity
control, although it will reduce other indoor air pollutants.
Of course, if the RenewAire system is set up to exhaust from
the bathrooms, you can use it for that purpose year-round.
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So
should I use the RenewAire system with air conditioning?
RenewAire
systems work very well with air-conditioning - much better than
sensible-only heat exchangers. As in the winter, if you keep
your house closed up tight, (as you should when air-conditioning),
indoor air quality will suffer. The only real difference is
that air-conditioning systems do have some moisture-removal
capability, unlike heating systems. Exactly how much water the
air-conditioner will remove depends on how it is set up.
If
you operate your air-conditioning system day after day, keeping
your home closed up tight, you should use your RenewAire system
to ventilate. It will bring in fresh air, just as it does in
the winter. The fresh air from the RenewAire will be warmer
and moister than the house air, but it will be cooler and dryer
than the outside air. As in the winter, the operating cost to
ventilate with RenewAire will be very low.
Finally,
some people like to use RenewAire in the summer just so they
can ventilate without opening windows, either for security or
to avoid rain coming in open windows. That works well, and RenewAire
always allows you to bring in fresh air that is as close as
possible to your inside air temperature and humidity.
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I
have a spa room, and the only pollutant I'm worried about is
humidity. Do I have to use the moisture recovery feature?
Spa
rooms and pool enclosures are two of the rare applications where
units that don't transfer moisture are a better choice. As a
rule of thumb, if a spa room is less than third of the total
exhaust air volume, a RenewAire unit can still be a good choice.
Almost all other situations are better served by RenewAire's
standard core.
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What
is the RenewAire core made of?
The
RenewAire core is a carefully designed, highly engineered resin
composite material, developed over thirty years ago specifically
for energy-recovery ventilation systems. It resembles corrugated
paper, but it really isn't - any more than the high-tech tires
on modern cars resemble the rubber in pencil erasers. The RenewAire
material has been imitated, but its optimized balance of high
heat transfer, moderate moisture transfer, and low gas transfer
rates has never been reproduced.
RenewAire's
hydroscopic resins act as highly selective molecular "conveyer
belts" or "water pipes", that carry water vapor
as individual molecules from one side of each heat transfer
membrane to the other. Very low numbers of extraneous molecules
are carried across the membrane.
Another
way to think of how RenewAire works is as a special type of
window material. Glass in a window lets both light and heat
enter your home, while keeping out dirt and outside air. The
material in RenewAire lets through heat and water vapor, but
doesn't let air or other gases through.
Installations
employing this technology began in the U.S. during the late
1970's. Today over 60,000 units are in service throughout North
America.
Several
competitors have recently offered another fixed-plate enthalpic
element. They use a completely different approach to moisture
transfer: porosity. The material has relatively large pores
that allow a number of different molecules to pass freely between
air streams, without any screening. That means that carbon dioxide
is recovered in dramatically higher percentages than in the
RenewAire core. These products also have slightly lower in sensible
performance, and have virtually no track record.
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Enthalpic
energy recovery seems to deliver a number of benefits. Do any
other manufacturers offer this kind of technology?
A
few competitors use different approaches to provide the heat-
and moisture-recovery functions of the RenewAire core. We feel
they do not succeed in matching the overall performance superiority
of RenewAire.
Besides
the plate exchange units that imitate but do not match RenewAire
performance, there are other types of enthalpic approaches using
the "desiccant-coated heat wheel". This approach can
provide relatively high energy-recovery performance. But it
has major liabilities that degrade its overall value: high maintenance,
difficulty of installation, and wheel seal cross-leakage. The
drive belts are scheduled for replacement every two years. Hanging
these units and connecting ducts are difficult and time-consuming.
The technology requires use of an electric pre-heater to prevent
frost damage in northern climates. Finally, these units have
10%+ cross-leakage of exhaust air back into the fresh air past
the seals around the moving wheel, and there may be additional
carry-over of water-soluble pollutants in the desiccant.
While
enthalpic heat wheels can perform well in large, tightly engineered
systems utilizing molecular sieves and purge cycles, at residential
scales they are an expensive alternative- more potential trouble
than they are worth.
No
other enthalpic-transfer technology available today delivers
all the benefits of RenewAire.
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Why
doesn't the RenewAire core freeze up?
For
the very simple reason that no condensate forms. Without water
in the liquid phase, no solid ice forms in the RenewAire core,
which can keep functioning without interruption in typical winter
conditions.
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Does
the RenewAire core itself block up with dust?
No.
Once air enters the core itself, its velocity is too high for
air-borne particles to settle out. Even in smoky bars, the interior
of the core stays remarkably clean. Vacuuming off the face is
sufficient to keep it functioning properly.
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The
RenewAire's energy-transfer core is designed to transfer some
water vapor. Does that mean it will transfer other pollutants
as well?
The
core in RenewAire was designed to transfer an optimum amount
of water vapor (in the gas state) and a minimum amount of other
gases. The RenewAire core has low levels of transfer of other
gases, and excellent separation of the two airstreams themselves.
The transfer levels are documented for a number of gases of
interest; for example, the transfer rate for carbon dioxide
is about 3%, that for gases in smoke is less than 2%. This is
far better than any competitors' residential-scale enthalpic
transfer systems.
RenewAire
is not designed for the removal of toxic or highly dangerous
vapors, as might be found in a laboratory. It is designed to
reduce and control the concentration of typical pollutants already
found in the home, using a dilution strategy. So a low level
of transfer of some of the exhausted pollutants poses no problem
in almost all cases. In unusual instances where a specific gas
pollutant is of interest, we may be able to provide data on
recapture behavior.
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With
all that water being transferred I'm worried about germs and
bacteria building up in the unit. Does that happen?
Laboratory
tests confirm that RenewAire is not hospitable to microrganisms.
In the RenewAire core, moisture is transferred as a gas, not
as liquid water. By staying dry, the core denies germs the environment
in which to propagate. In fact, bacteria deliberately injected
into the RenewAire core material was found to have died within
a short time.
In
contrast, consider the situation in the typical condensing-type
air-to-air heat exchanger constructed of metal or plastic. In
many conditions, water is condensing in the core, draining out
over wetted surfaces, then being collected in drain pans. This
is the perfect environment for biological growth.
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How
is the system installed?
The
RenewAire unit is usually installed on a wall inside the mechanical
room. Two insulated ducts connect the unit to the outside: one
to get rid of stale air from the house, one to bring in fresh
air from outside. One, two, or more ducts are used to collect
stale air in the house, often in bathrooms; these are connected
directly to the RenewAire unit. The fresh, tempered air provided
by the unit can be ducted into the home's furnace or air-conditioning
ductwork.
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Do
I need a forced-air heating system to install RenewAire?
RenewAire
can be installed in homes with any kind of heating system. With
hot-water heat, for example, it's easy to install a duct from
the RenewAire to one or two central locations in the home. Very
simple installations can be very effective.
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Why
doesn't RenewAire need a condensate drain?
RenewAire
is different from many other air-to-air heat exchangers because
it is designed to transfer both heat and moisture from one air
stream to the other. This very special feature eliminates condensation
under almost all conditions. For example, in typical winter
weather, the warm, relatively moist household air transfers
most of its heat to the incoming air stream as it passes through
RenewAire's core. It also transfers just enough of its moisture
to the incoming air to avoid condensing. This moisture is in
the gas state so the inside of the RenewAire stays dry, unlike
most other products that collect the moisture as liquid water
and must drain it away.
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So
I can install RenewAire anywhere - even in a room without a
floor drain?
Some
locations are easier than others, but RenewAire can be installed
almost anywhere, as long as they are accessible for changing
filters. Even better, a RenewAire unit can be installed in any
convenient position, because there are no drain pans that must
be located at the bottom of the unit.
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Do
I need many special accessories to install RenewAire?
RenewAire
units are easy to install with the standard duct components,
grilles, wall caps, and controls that most wholesalers already
stock. You can use the same style wall grilles as in the rest
of your heating or cooling system, and virtually any line-voltage
controls will work with RenewAire. Heating contractors often
have the components they need to install RenewAire in their
service trucks already. Of course, RenewAire also provides a
line of controls and accessories that are convenient to install
and use.
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How
should I control my RenewAire system?
Some
manufacturers suggest you run their ventilation products continuously:
"just plug it in and walk away". We believe it makes
more sense to run RenewAire on a controlled basis: "run
it only to provide the ventilation you need". Most people
elect to control RenewAire systems with a proportional timer,
a 24 hour timer, or with a dehumidistat. Use a dehumidistat
if your primary concern is controlling excess wintertime moisture.
Use a timer otherwise, particularly if you plan to operate the
system in the summer, or are worried about indoor air pollutants
originating from building materials.
It
is also possible to install manual switches in bathrooms, since
many installations use the RenewAire system to provide bathroom
exhausts. These can be push button activated timers, spring-wound
timers or simple on-off switches.
In
the future, expect to see more sophisticated control schemes,
including occupancy and carbon dioxide sensors. Costs for these
controls, which are already showing up in larger installations,
continue to come down.
Other
control schemes can make sense too. The main point is to make
sure the system runs regularly to provide plenty of ventilation.
Most systems run almost all the time; in early winter, for example,
many systems need to run twenty-four hours a day to control
excess moisture.
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Why
is RenewAire a single-speed unit? Isn't low-speed operation
more efficient?
We
believe its best to operate a RenewAire - or any other unit
- at its full rated speed. This provides the best overall performance,
when considering the amount of air moved, the electrical efficiency
of the blower, and the total energy recovered. Let's take those
points in order:
The
primary goal of an energy-recovery ventilator is to ventilate.
RenewAire systems are designed to run for all or most of the
day, moving enough air over a day's time to control the pollutants
generated inside the home that day. Most competitors' products
can't provide sufficient ventilation rates without running on
their high speed much of the time.
Blower
wheels in fans are designed to move the most air per watt at
a certain speed, generally its full, or "top" speed.
At lower speeds, the wheels perform less efficiently, and the
electric motors driving the wheels are less efficient too. So
a given blower will use less electricity to move a given amount
of air at its full speed than it will at its half speed.
While
the energy recovery efficiency of any heat-transfer core will
go up as air speeds go down, there is less energy to recover
because less air is being moved. So the total amount of energy
recovered is less at lower speeds than at high speeds. It's
a little like the mileage figures your car delivers while it's
standing still: your engine uses very little fuel while its
idling, but because you aren't going anywhere, your mileage
is infinitely poor!
Besides
keeping the product simple and inexpensive, single-speed blowers
are less likely to fail, and our overall heat exchange effectiveness
is so much higher than most others, that we can just operate
the RenewAire at full speed for the period as needed.
Other
manufacturers like multiple fan speeds because they can use
the efficiency figures they get at very low speeds to make their
cores look better. Our efficiency numbers look better at low
speeds, too. But remember to compare the efficiencies of competitor's
products when operating at the speeds necessary to deliver ASHRAE-recommended
ventilation rates! At comparable airflow rates we beat almost
everybody - even before considering the latent energy only we
can recover. In fact, at our rated "high" speed we
deliver recovery effectiveness better than most of our competitors
achieve at their low speeds!
Some
people like the idea of the ventilation system running constantly,
with high-speed operation as needed to control humidity or to
ventilate bathrooms. But ASHRAE accepts regular, intermittent
ventilation as an effective strategy. We feel there is no significant
advantage to the "constant low-speed/boost" strategy,
and plenty of disadvantages. This is particularly apparent if
you would try to detect any airflow from the furthest grill
on a competitors unit running at half speed. You need to move
air to provide effective ventilation.
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How
expensive is RenewAire to run?
The
blowers in RenewAire products are very inexpensive to operate.
Take an EV130 RenewAire unit, running 90% of the time during
a six-month heating season. The blower cost will be about $34
for that period - less than 20¢ a day (with electricity
at 7¢ per kWh).
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Will
my heating or cooling costs go up?
Because
RenewAire recovers most of the heat energy in the exhaust air
(in the winter), this is the least expensive kind of ventilation
system to operate. RenewAire is also much less expensive to
operate than a dehumidifier sized to accomplish a similar amount
of wintertime moisture removal.
In
fact, most people report little or no impact on their heating
or cooling bill, but this can vary depending on many factors.
Sometimes the RenewAire system replaces ventilation practices
(like opening windows) that were formerly used - so while the
total ventilation rate goes up, energy cost doesn't change,
or even goes down. And, in some cases, the balanced ventilation
feature of RenewAire may reduce the household pressurization
that normally drives natural infiltration.
If
all these factors are ignored, it is possible to estimate the
worst-case additional cost to replace the additional energy
that RenewAire can't recover from the exhaust air. For a typical
2500 square foot house in the upper Midwest or New England,
in a 7000-degree day, six-month heating season, that additional
energy might cost $30 to $40 with gas or oil heat. So the total
cost of fresh air in this example would be less than 40¢
per day (including electricity for the blowers).
Without
energy recovery, the cost to heat the incoming fresh air might
be $100 to $140. The savings are even greater with electric
heat. Variations from house to house do make it hard to calculate
the savings. But without question, energy recovery, as a feature
of a ventilation system, does generate a payback through reduced
energy costs - in addition to the other benefits a ventilation
system provides.
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What
maintenance is required?
Filter
cleaning is the main regular maintenance item. The easiest way
to clean the long-lived filters is vacuum them with a hose attachment.
Inexpensive replacement filters are available. The installing
HVAC contractor is the primary contact for replacement filters.
As an alternative, you may want to make your own filters. Filters
may be cut from a sheet of 3/4"-1" firm, spun polyester
"hog hair" filter media or material, similar to the
existing green/blue filter in the residential unit. Cut to the
existing size of the filter and install between the core and
the incoming air stream. For all other inquiries, please contact
RenewAire LLC.
Once
a year the RenewAire core itself should be vacuumed off, and
that is a good time to vacuum out any other dust found inside
the unit.
Finally,
the outside wall caps where fresh air is brought in, and where
stale air is exhausted, should be checked seasonally to make
sure they are not blocked.
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What
is the life expectancy of the RenewAire core?
The
RenewAire core was designed to perform with a service life of
20+ years. Since introduction of the technology in the early
1970's, millions of these cores have been operating throughout
the world with a virtual zero failure rate. Moreover, it has
been well documented that both heat and moisture characteristics
of RenewAire cores have not changed significantly when measured
over time.
Among
our competitors' desiccant-coated heat wheels, on the other
hand, few are expected to perform optimally for more than 10
years.
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How
about the life expectancy of the rest of the RenewAire unit?
The
only moving parts in RenewAires are the blowers. The blowers
used have a rated mean run time until failure of 80,000 hours.
That is equivalent to over thirty-three hundred days of continuous
operation (Or twelve years if used continuously for nine months
out of every year). Filters may require replacement, depending
on the method used to clean them.
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