It is not one lifespan
The question assumes encapsulation is a product. It is a system of several components with genuinely different service lives, installed together and warrantied separately. Asking "how long does it last" is a bit like asking how long a kitchen lasts — the cabinets and the dishwasher are not on the same clock.
That matters practically, because the component most likely to fail first is also the cheapest to replace, and the component people worry about most is the one least likely to be the problem.
Component service lives
| Component | Realistic expectation | What ends it |
|---|---|---|
| Liner (the plastic itself) | The longest-lived element. Commonly sold with 20–25 year material warranties. | Rarely the material. Punctures from people working under the house, or abrasion in a space that gets used for storage. |
| Seam tape and seals | The realistic maintenance item. Expect to inspect, not to ignore. | Adhesion loss over time, especially where the liner meets stem walls, piers and penetrations. |
| Mechanical fasteners / wall attachment | Long, if correctly specified for the substrate. | Pulling out of soft or damp masonry, or under-specified fasteners on the original install. |
| Dehumidifier, if fitted | An appliance. Budget for it as one. | Compressor or fan failure, blocked condensate line. Often the first component replaced. |
| Exhaust fan (Washington sealed crawl spaces) | A fan that runs around the clock, which Washington’s code asks of every sealed crawl space. An appliance; this page cites no service life for it. | Motor and bearing wear from continuous running, or a fan switched off and forgotten. |
| Sump pump, if fitted | Manufacturers generally cite something like 7–10 years for residential pumps in normal duty. | Duty cycle. A pump running through every October-to-March wet season sits at the short end. |
| Rim joist air sealing / foam | Effectively permanent once cured and undisturbed. | Being cut into for later work and not properly resealed. |
Note what this table implies. Nobody replaces "an encapsulation." They replace a dehumidifier, or re-tape a run of seam, or patch a puncture. The liner outliving several fans and dehumidifiers is the normal case, not the exception.
What actually ends an encapsulation early
In practice, systems that fail well short of expectations usually fail for one of these reasons, and only one of them is about the materials:
- It was installed over an unresolved water problem. By some distance the most common cause. A liner is moisture control, not water management. Water that still enters the crawl space now runs under the liner, where it is invisible, unevaporated, and sitting against framing. Systems installed this way can be functionally compromised within a season or two while looking perfect from the hatch.
- Nobody looks at it. Sealed gets read as finished. A seam that lifted in year three is trivial to re-tape and expensive to discover in year eight.
- The exhaust fan or dehumidifier failed silently. No alarm, no monitor, nobody in the crawl space. The space is now sealed without the air control it was designed around, which is worse than the vented space it replaced.
- Somebody worked under the house. A plumber, an electrician or a cable installer crawling over a liner will puncture it, and will not re-seal it. This is routine and worth planning for rather than treating as bad luck.
- The condensate line clogged. A dehumidifier discharging into a blocked line puts the water it just removed back into the space.
- The scope was thin to begin with. A liner laid loose on the ground with no wall coverage and unsealed seams was never an encapsulation, whatever the invoice said. It is a vapor barrier, and it will behave like one.
Point one is worth restating because it drives the others: the durability of an encapsulation is set mostly by the quality of the diagnosis that preceded it, not by the thickness of the plastic. This is also why an inspection that identifies water intrusion before the liner goes down is worth more than an upgrade from 12-mil to 20-mil.
Reading the warranty
Warranty length is the number most often quoted as lifespan, and the two are not the same thing. A 20-year material warranty is a manufacturer's commitment about the material, usually excluding punctures, installation defects, and anything caused by water intrusion. Questions worth asking in writing:
- How many warranties am I getting? Liner material, installation workmanship and dehumidifier are typically three separate ones from three different parties.
- What voids it? Water intrusion exclusions are common and are exactly the scenario most likely to occur.
- Does it transfer on sale, and is there a fee?
- What is the remedy? Replacement material only, or material and the labor to install it? The labor is most of the cost.
- Is annual inspection a condition? Some workmanship warranties require it and lapse without it.
- Who honors it if the contractor closes? A manufacturer-backed warranty survives a contractor going out of business; a contractor-backed one may not.
Verify the contractor's standing before relying on a long warranty from them. In Washington every construction contractor must be registered with the Department of Labor and Industries, bonded and insured, and L&I's Verify search shows a contractor's registration, bond and any lawsuits against the bond (how to read the record). A 25-year warranty is only as good as the entity behind it.
Maintenance that actually extends it
Modest and infrequent, but not zero. Roughly annually, and ideally before the wet season rather than during it:
- Read the humidity. A monitor with a remote display means you check it from the hallway rather than the crawl space. This is the single highest-value habit, because it catches a silent fan or dehumidifier failure.
- Check the exhaust fan is running, in a sealed crawl space, and that its outlet is clear.
- Look at the seams, particularly where the liner meets stem walls and piers.
- Check for punctures after any trade has been under the house — and tell them the crawl space is encapsulated before they go in.
- Clear the dehumidifier's condensate line and clean its filter.
- Test the sump pump, if there is one, before the rains rather than after.
- Check the exterior. Downspout extensions and grading are what keep water away from the system in the first place.
The seasonal maintenance checklist covers the wider walkthrough, including the pre-rain and post-rain checks that apply whether or not the space is sealed.
What does it cost to own for 10 or 15 years?
Every crawl space quote is a purchase price. None of them is a cost of ownership, and the difference is not small — because the components that fail are not the component being sold. Below is the same scope priced both ways.
That gap is the whole point of this section, and it is not a criticism of anyone's quote. A contractor quoting an installation is quoting an installation. But a homeowner deciding between a $3,400–$4,675 vapor barrier and a full sealed system is making a fifteen-year decision using a one-day number, and the two scopes do not carry the same fifteen-year tail.
The inputs, and what each one rests on
Read this table before the totals. It is the part that decides whether the totals are worth anything. Each row shows where its service life comes from and where its price comes from, because those are two different questions and they have two different answers.
| Component | Service life | Where that comes from | Cost of one occurrence | Where that comes from |
|---|---|---|---|---|
| Dehumidifier The first thing you will replace, and the only component in a normal encapsulation that is an appliance. Its failure is silent: a sealed crawl space with a dead dehumidifier is worse than the vented one it replaced. | 8 years | Industry reference see citation | $1,350–$2,700 | Published site range The published Seattle-metro range for a dehumidifier supplied, installed and wired ($1,350–$2,700). Used unchanged for a replacement, which is conservative: a like-for-like swap into an existing circuit does not repeat the electrical work. |
| Sump pump Duty cycle sets the life. A pump that runs through every wet season sits at the short end of any published figure, and a pump that has never run is not proof of a dry crawl space — it is equally consistent with a stuck float. | 7 years | Industry reference see citation | $1,600–$3,125 | Published site range The published Seattle-metro range for a sump pump installation ($1,600–$3,125), which covers the pump, basin, lid, discharge plumbing and the electrical connection. A replacement pump dropped into an existing basin is the bottom of this band or below it. |
| Dehumidifier air filters The one maintenance item with a manufacturer-stated interval. Running the unit on a blocked filter reduces its capacity, so this is a small cost that protects a large one. | Recurs annually | Manufacturer see citation | $50–$180 per year | Editorial allowance Per year. The interval is the manufacturer’s — Therma-Stor recommends the air filters be replaced every three to six months, so two to four a year. The price per filter is NOT sourced: this site found no published Seattle-area figure and holds none, so the annual band assumes roughly $25 to $45 a filter. Substitute the price on the unit you actually own. |
| Annual inspection and service visit Some workmanship warranties lapse without one, which makes this a condition of the coverage as often as it is a discretionary spend. Read the warranty before deciding it is optional. | Recurs annually | Assumption | $150–$350 per year | Editorial allowance Per year, for one professional crawl space visit. Entirely an editorial assumption: this site found no published Seattle-area rate for a crawl space service call and holds no quote data for one. It is in the model because leaving it out would imply the maintenance is free, and it is shown separately so it can be removed. |
| Seam, seal and wall-attachment repair Not the plastic failing. A taped seam letting go at a stem wall, a fastener pulling out of damp masonry, or a puncture left by a trade who did not know the crawl space was sealed. Cheap in year three, expensive to discover in year eight. | 7–15 years | Assumption | $270–$935 | Editorial allowance Modeled at 8% to 20% of the published Seattle-metro vapor barrier installation range ($3,400–$4,675), giving $270–$935 for a localised repair visit. Both the percentage and the 7-to-15-year interval are editorial judgements with no source behind them. At the low end of the interval the model books none of these inside 15 years; at the high end it books two. |
Two tiers, kept apart on purpose.
Rows marked published site range trace to this site's cost methodology — the same modeled ranges the cost guide publishes, with a documented reference project behind them. Rows marked editorial allowance do not. Nobody publishes a Seattle-area rate for a crawl space service call, and this site holds no quote data for one, so those figures are judgements with their reasoning printed rather than measurements with a source. Every total below is shown as both subtotals so you can take the first and discard the second.
Three scopes, modeled over 10 and 15 years
These are the site's own service scopes, not invented tiers. Installation figures come from the published cost ranges; the derivation is printed under each one so a reader can check the addition rather than trust it.
Encapsulation with dehumidification
The base scope this model prices. Sealed liner on floor and walls, vents and access sealed, seams and penetrations sealed, plus a dehumidifier. The dehumidifier is this model’s choice of equipment, not a code item: Washington’s residential code (WAC 51-51-0408, R408.3), which governs new construction and permitted work, lists a radon system and continuous exhaust ventilation for an unvented crawl space instead, and neither is in this price.
The honest fit: A damp crawl space with no standing water and no active water entry. If water gets in, this is the wrong scope at any price.
| Horizon | Installation | Expected replacements | Published-range subtotal | Editorial allowance | Modeled total |
|---|---|---|---|---|---|
| 10 years | $12,000–$15,700 |
| $13,350–$18,400 | $2,000–$6,235 | $15,350–$24,635 |
| 15 years | $12,000–$15,700 |
| $13,350–$18,400 | $3,000–$9,820 | $16,350–$28,220 |
How the installation figure was assembled: The published encapsulation range ($10,650–$13,000) plus the dehumidifier, which that range excludes and quotes separately ($1,350–$2,700).
Premium conditioned crawl space
The full premium scope as published: heavier liner, dehumidifier, closed-cell foam at the rim joists, and the harder-access or larger-area work that pushes a project into the premium band.
The honest fit: Low clearance, a large floor area, difficult access, or an owner buying the heavier material deliberately. The premium band is a different scope, not a more expensive contractor.
| Horizon | Installation | Expected replacements | Published-range subtotal | Editorial allowance | Modeled total |
|---|---|---|---|---|---|
| 10 years | $15,675–$21,500 |
| $17,025–$24,200 | $2,000–$6,235 | $19,025–$30,435 |
| 15 years | $15,675–$21,500 |
| $17,025–$24,200 | $3,000–$9,820 | $20,025–$34,020 |
How the installation figure was assembled: The published encapsulation premium band ($15,675–$21,500). The dehumidifier is NOT added on top: this band already includes it, along with the rim joist foam. Adding it again is the double-count this line exists to prevent.
Encapsulation over a water-management system
Drainage first, then the sealed system on top of it. Interior perimeter drain, sump basin and pump with a battery backup, then the encapsulation and its dehumidifier.
The honest fit: Water actively enters the crawl space. This is the configuration with the most equipment on the ownership clock, and the one where the gap between purchase price and cost of ownership is widest.
| Horizon | Installation | Expected replacements | Published-range subtotal | Editorial allowance | Modeled total |
|---|---|---|---|---|---|
| 10 years | $16,675–$23,775 |
| $19,625–$29,600 | $2,000–$6,235 | $21,625–$35,835 |
| 15 years | $16,675–$23,775 |
| $21,225–$32,725 | $3,000–$9,820 | $24,225–$42,545 |
How the installation figure was assembled: The published encapsulation range ($10,650–$13,000) plus the dehumidifier ($1,350–$2,700), plus crawl space drainage ($4,025–$7,175), plus the battery-backup increment derived from the sump pump row’s typical and premium bands ($650–$900).
What would move these numbers
The dehumidifier's service life is the input the totals move most with, and it is the one resting on an industry guideline chart rather than on a measurement. So here is what happens if the chart is wrong, tested against the common scope over fifteen years:
| If a dehumidifier lasts | Replacements in 15 years | Change against the published model |
|---|---|---|
| 6 years | 2 | +$1,350–$2,700 |
| 8 years — the figure used | 1 | No change |
| 12 years | 1 | No change |
Notice the third row. Over a fifteen-year window, any dehumidifier lasting between about seven and a half and fifteen years produces exactly one replacement, so the model cannot tell a good unit from a very good one. That is a real limit of a whole-number replacement count over a short horizon, and it is worth knowing before treating any of these totals as precise.
What these totals leave out
A cost-of-ownership figure that quietly omits the electricity is not a cost of ownership. Each of these is a real cost with no defensible Seattle-area price behind it, so each is named rather than absorbed silently. Treat the totals above as a floor, not a forecast.
- Electricity to run the dehumidifier Pushes the total up
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A dehumidifier in a sealed crawl space runs whenever the space is above its humidity setting, and the electricity it uses is billed at whatever your utility charges per kilowatt-hour.
Why it carries no figure here: The DOE test procedure behind published dehumidifier energy figures measures portable room units on a standardised cycle. Applying that number to a crawl space unit under a Seattle-area house would be a fabrication with a federal test procedure’s name attached to it. Actual consumption depends on run hours in your crawl space, which nobody knows in advance.
- Radon vent system and exhaust ventilation, where a permit applies Pushes the total up
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Washington’s residential code section for under-floor space (WAC 51-51-0408, R408.3) does not list a dehumidifier among its conditions for an unvented crawl space. It lists a sealed Class I vapor retarder together with a radon system meeting the code’s radon appendix, and continuously operated mechanical exhaust at 1 cubic foot per minute for each 50 square feet of crawl space floor. That code governs new construction and permitted work.
Why it carries no figure here: No modeled range for a radon vent system or a crawl space exhaust fan exists on this site, and the encapsulation range excludes both. Whether either is required on an existing house is a question for the local building department, not for a cost model.
- Backup sump pump battery Pushes the total up
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Zoeller states the sealed AGM battery for its Aquanot backup systems is designed to deliver a useful life of 4 to 5 years — so a 15-year horizon contains two or three of them.
Why it carries no figure here: The manufacturer publishes the design life but no price, and this site found no published Seattle-area figure for a replacement battery. The service life is genuinely useful on its own and is reported; inventing a price to sit next to it would not be.
- Condensate pump, where the drain has no fall Pushes the total up
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A dehumidifier needs somewhere for the water to go. Where gravity drainage is not available a condensate pump does it, and it is another small motor on its own clock.
Why it carries no figure here: No manufacturer or industry service-life figure that specifically covers a residential crawl space condensate pump was found, and this site found no published Seattle-area price. A figure from a commercial-building survey is not a residential figure and is not offered as one.
- Dehumidifier repairs inside the warranty term Pushes the total up
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Therma-Stor warrants its Santa Fe product for two years and its components for six — but beyond the two-year term the warranty excludes transportation and the labor to fit the covered part.
Why it carries no figure here: Whether a unit fails in year four at all is unknowable, and the labor rate to fit a warranty part is the same unpublished local service rate that keeps the annual visit in the allowance tier. Worth knowing that a six-year component warranty is not six years of free repairs.
- Insulation replacement Not a running cost
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Replacing crawl space floor insulation is published on this site at $2,500–$5,825.
Why it carries no figure here: It is not an encapsulation running cost — it is the cost a working encapsulation is partly there to stop recurring. Booking it as a maintenance item would double-count the benefit as an expense. It belongs on the other side of the ledger, and this model does not attempt a benefits side.
- The water problem nobody diagnosed Pushes the total up
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The single most common reason an encapsulation fails early is that it was installed over unresolved water intrusion. Drainage retrofitted afterwards is published here at $4,025–$7,175.
Why it carries no figure here: It is not a maintenance cost and not a probability this site can honestly put a number on. It is the largest single risk to any figure on this page, and the reason the diagnosis matters more than the material thickness.
What it means for the money
This site models a Seattle-metro encapsulation at $10,650 to $13,000 before sales tax, up to $15,675–$21,500 for a full premium scope, with the radon system and exhaust fan Washington asks of a sealed crawl space priced on top. Two honest observations about amortizing that:
- Dividing the full price by a liner warranty term flatters the arithmetic, because it ignores the fan and any dehumidifier you will replace inside that window and the maintenance the warranty may require.
- It also understates the case in a different way, since the largest reported benefits — a dry crawl space, no musty smell reaching the living space, warmer floors — arrive immediately rather than accruing over the term.
Both of those observations are why the section above exists: the first is the arithmetic error the ownership model is built to avoid, and the second is the reason the model does not pretend to be a verdict on whether the work is worth doing. It prices one side of the ledger only.
If you are weighing the spend rather than the service life, is encapsulation worth it in Washington works through the payback math for this climate, and vapor barrier vs encapsulation covers whether the cheaper option would do the job. If you have not yet decided whether your crawl space should be sealed at all, closed vs vented crawl spaces is the prior question, including what Washington code requires.
Warranty terms belong to the installer and to the manufacturer of each component, and they differ, so read the written terms themselves rather than a summary of them. A free in-home inspection is how to find out what your crawl space needs before you evaluate anyone's warranty. You get a written, no-obligation quote; ask for it to name the liner, the exhaust fan, the radon vent, any dehumidifier and any pump by product, so the service lives above can be checked against it.
Sources
An honest limitation: the component service lives on this page come from manufacturer documentation and from the home-inspection industry's own reference chart, not from a controlled study or from field data this site holds. No published study tracks crawl space encapsulation lifespans in the Seattle area, and no source prices crawl space maintenance here — which is why the ownership model separates its published-range subtotal from its editorial allowance, and why the allowance figures are labeled as assumptions rather than cited to anything. Treat the service lives as informed expectations rather than measured outcomes. What Washington's code requires of a sealed crawl space, how to check a contractor's registration, and the moisture thresholds that separate mold from decay, are cited below.
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Washington State Legislature, WAC 51-51-0408 — Section R408, Under-floor space (Washington State Residential Code, amended by WSR 23-23-104) Checked
What Washington requires under a house: ventilation at 1 square foot per 300 square feet of under-floor area; 6-mil black polyethylene ground cover with joints lapped 6 inches, extending to the foundation wall, which may be omitted where the crawl space has a concrete slab floor at least 2 inches thick; vent coverings with a least dimension of no more than 1/4 inch (corrosion-resistant wire mesh at 1/8 inch), and operational louvers permitted; ventilation reducible to 1/1,500 where a Class I vapor retarder covers the earth, with a radon vent built to Appendix AF required where ventilation is below 1/300 or operable louvers are installed. Vents may be omitted only where both numbered conditions of R408.3 are met: a continuous Class I vapor retarder lapped and sealed 6 inches, extending 6 inches up and sealed to the stem wall, with an Appendix AF radon system; and continuously operated mechanical exhaust at 1 cfm per 50 square feet. R408.8 is not adopted in Washington.
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USDA Forest Products Laboratory, Wood Handbook, Chapter 14: Biodeterioration of Wood (General Technical Report FPL-GTR-282 (2021 edition)) Checked
The wood moisture content and temperature ranges at which decay fungi become active, which is what separates a surface mold problem from structural rot. Also, for the white-mold guide: mold shows as fuzzy or powdery surface growth in colors from light shades to black, and on softwoods can often be brushed off (p. 14-2); mold and stain fungi affect strength only slightly but make wood more absorbent, which can lead to decay (p. 14-2); fresh surface growth of decay fungi can look like fan-shaped patches, strands or root-like structures, usually white or brown (p. 14-3); white rot leaves wood bleached and spongy, brown rot darkens it and cracks it into cubes, and some brown-rot fungi form water-conducting strands that carry soil water into dry wood (p. 14-4); and that crawl-space condensation, whose primary source is soil moisture, can cause serious decay, while wood debris and concrete forms left under a building can seed it (p. 14-7). And, for the termite guide (pp. 14-11 to 14-15): anobiid powder-post beetles generally need wood at about 15% moisture or more, which inadequate ventilation can create and lower moisture through ventilation, insulation and vapor barriers can relieve; subterranean termites need a constant source of moisture, build mud shelter tubes that are a good sign of their activity, swarm usually in early spring or fall, and leave galleries along the grain under a shell of sound wood, so suspect wood is probed with a pick or knife; infestation hazard is greatest over a crawl space that is poorly drained and lacks a moisture barrier; in a crawl space, joists at least 18 inches and girders 12 inches from the earth, a polyethylene barrier over the soil running partly up the foundation wall, drainage away from the house with gutters, downspouts and grading, posts that bear on the ground made of concrete, and concrete forms, stakes, stumps and waste wood removed; control of termites already in a building means breaking the contact between the soil colony and the woodwork by blocking runways, treating the soil, repairing leaks such as plumbing leaks, or a combination, then inspecting often; carpenter ants use wood for shelter rather than food, prefer wood softened by decay and so can point to a moisture problem, and species such as Camponotus modoc can be particularly damaging.
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United States Environmental Protection Agency, A Brief Guide to Mold, Moisture and Your Home Checked
Indoor humidity targets, EPA’s position on when sampling is and is not worth paying for, its position on biocides, the general health effects of damp indoor spaces, and the 24–48 hour drying window — which EPA states as a PREVENTION target ("dry water-damaged areas and items within 24-48 hours to prevent mold growth"), not as a time by which mold begins. Also that molds produce allergens, irritants and in some cases potentially toxic substances, can trigger asthma attacks in people allergic to mold, that it is impossible to get rid of all mold and spores indoors, that moldy surfaces should not be painted or caulked over, that a moldy area under about 10 square feet is in most cases a job a homeowner can handle, that larger growth sends the reader to EPA’s remediation guidance for schools and commercial buildings, and that damage from sewage or other contaminated water calls for a professional experienced with it.
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International Association of Certified Home Inspectors (InterNACHI), InterNACHI's Standard Estimated Life Expectancy Chart for Homes Explanatory summary, not the governing text Checked
The two equipment service lives the ownership-cost model turns on: a dehumidifier at 8 years and a sump pump at 7 years. This is the chart the home-inspection trade actually works from, which is why it is cited — an inspector reading a service life into a report is most often reading this one.
Note: An industry guideline chart, not a measurement. It states its own figures are determined from research and testing under regular recommended maintenance and normal wear, and should be used as guidelines only rather than relied on as guarantees. It publishes no sample, no method and no confidence interval, and it is not specific to the Seattle area.
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Therma-Stor LLC (Santa Fe), Santa Fe Advance90 / Advance120 Dehumidifier — Installation and Operation Instructions (TS-1152, Rev B, 08/20) Checked
Three things a dehumidifier costs money for after it is installed: the manufacturer’s recommendation that the air filters be replaced every three to six months; a warranty of two years on the product and six years on components; and the warranty’s exclusion of transportation and of labor costs incurred in repair or replacement of those components — which is why a six-year component warranty is not six years of free repairs. Also the installation conditions the dehumidifier guide relies on: the space must be free of water intrusion and of excessive outdoor air before the unit goes in; it runs between 49°F and 95°F, best from 56°F, and makes little or no water at 55°F or below; intake and exhaust stay 12 inches from any wall; it sits level and raised, never in standing water, and is hung from the joists where the space could flood, a flooded unit not being covered; it needs a 115-volt outlet on a circuit of at least 15 amps, dedicated and GFCI-protected near water; its drain needs a trap and a 3/4-inch line falling at least 1 inch in 10 feet, or a condensate pump; and its “Normal” setting, 45 to 55 percent relative humidity, is the one recommended for most uses, the driest setting being advised against in a space below 65°F because it means long stretches of ineffective running.
Note: One manufacturer and one product family. Cited because it is a crawl-space-class unit whose terms are published in full, not because its terms are universal. Confirm the filter interval and the warranty on the unit actually quoted to you; both vary by model and by brand.
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Zoeller Pump Company, AGM Maintenance Free Battery — product specification Checked
That the sealed AGM battery for the Aquanot 507 and 508 backup systems is designed to deliver a useful life of 4 to 5 years — the figure behind the ownership model treating a backup pump’s battery as a recurring cost rather than a one-off purchase.
Note: A manufacturer’s design life for one battery type on one backup system. Actual life depends on how often the backup is called on, which in a Seattle-area crawl space is a function of the wet season and of the primary pump’s condition.
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Washington State Department of Labor & Industries, Verify a Contractor, Tradesperson or Business Checked
The official Washington register: registration status, bond, workers compensation account standing, and lawsuits filed against the bond.
Sources last checked between and ; the date beside each one is when it was last opened. Where a figure comes from a document that is revised on a schedule, the edition or version is named above so you can confirm it against the current one yourself.