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Deal.ai › Compare

Master Flow Foundation Vent Cover vs Frost King Foundation Vent Foam Plug

The Master Flow cover is the sturdier, more permanent choice: aluminum, a snap-in screen, and a spring-loaded automatic flap that opens and closes with temperature. The Frost King plug is a foam block you press into the opening for winter and pull out in spring. Buy the Master Flow for year-round venting that keeps rodents and debris out; buy the Frost King if you want a simple seasonal seal for a vent that already has a screen. Owners of the Master Flow report easy installation, though some had to enlarge the hook hole and one had a hook break.

  • Choose the Master Flow if you want a permanent, rust-resistant cover that vents automatically and blocks rodents and debris.
  • Choose the Frost King if you want a tool-free foam plug to seal a crawl space vent for the cold months and remove in spring.

Prices

  • Master Flow Foundation Vent Cover: $14.37 at Max Warehouse (last seen Nov 9)
  • Frost King Foundation Vent Foam Plug: $10.88 at Amazon (last seen Nov 8)
  • Difference: the Frost King Foundation Vent Foam Plug is $3.49 cheaper than the Master Flow Foundation Vent Cover at the latest prices (Nov 8 and Nov 9)
Master Flow
Master Flow 7.4 in. H X 15.4 in. W Mill Aluminum Foundation Vent Cover

Master Flow Foundation Vent Cover

Master Flow 7.4 in. H X 15.4 in. W Mill Aluminum Foundation Vent Cover

4.8(4 ratings)
$14.37at Max WarehouseChecked 23 h ago
See all prices and details
Visit Max Warehouse
Pros
  • Aluminum resists rust and corrosion
  • Automatic flap vents without manual work
  • Screen keeps out insects and small rodents
  • Two covers and springs per pack
  • Snap-in mounting, hardware included
Cons
  • Hook hole may need enlarging on some vents
  • At least one owner reported a hook breaking
  • Not paintable or stainable
  • Only fits 16 x 8 in. vents
Frost King
Frost King 6.5 in. x 7.75 in. Large Foundation Vent Foam Plug

Frost King Foundation Vent Foam Plug

Frost King 6.5 in. x 7.75 in. Large Foundation Vent Foam Plug

$10.88at AmazonChecked Nov 8
See all prices and details
Visit Amazon

As an Amazon Associate, Deal.ai earns from qualifying purchases.

Pros
  • No tools, presses in by hand
  • Seals the full opening for winter
  • Helps reduce frozen pipe risk
  • Easy to remove in spring
Cons
  • No screen or venting when installed
  • Foam can compress or degrade over seasons
  • Fits only smaller openings
  • Must be removed and stored each year

What separates them

Master Flow Foundation Vent CoverFrost King Foundation Vent Foam Plug
FunctionAutomatic flap opens and closes with temperature to vent the crawl space year-roundSolid foam plug seals the vent shut for winter insulation
Material and durabilityAluminum, rust and corrosion resistant, about 1/4 in. thickFoam and polystyrene, soft and compressible
InstallationSnap-in over a 16 x 8 in. vent; springs and screen includedPressure fit by hand, no tools
Rodent and debris screenScreen included to keep out insects and small rodentsNo screen; blocks the whole opening when in place
Seasonal useStays mounted all yearMeant to go in for winter and come out for summer
Fit rangeFits standard 16 x 8 in. foundation ventsFits openings around 6.5 x 7.75 in.
FinishMill aluminum, not paintable or stainableWhite foam

Price history

$14.60$2.86
Nov 4Nov 10
  • Master Flow Foundation Vent Cover: lowest $14.60 on Nov 4 at The Home Depot.
  • Frost King Foundation Vent Foam Plug: lowest $2.86 on Nov 9 at Lowe's; $9.62 on Nov 10.

Prices at every store

Master Flow Foundation Vent Cover

  • Max WarehouseNew

    In stockReturn policy

    $14.37Checked 23 h ago
    Visit Max Warehouse
  • Mrosupreme.comNew

    In stockReturn policy

    $14.41Checked 23 h ago
    Visit Mrosupreme.com
  • SupremeDIYNew

    In stockReturn policy

    $17.94Checked 23 h ago
    Visit SupremeDIY
  • The Home DepotNew

    Availability unknown

    $14.60Checked Nov 4
    Visit The Home Depot
All 8 stores and price history →

Frost King Foundation Vent Foam Plug

  • Lowe'sNew

    Availability unknown

    $2.86Checked Nov 8
    Visit Lowe's
  • WalmartNew

    Availability unknownSold by SIM Supply Inc

    $9.62Checked 5 h ago
    Visit Walmart
  • AmazonNew

    Availability unknown

    As an Amazon Associate, Deal.ai earns from qualifying purchases.

    $10.88Free shippingChecked Nov 8
    Visit Amazon
  • eBayNew

    Availability unknownSold by dkhardware (98.7% positive, 18,900 ratings)Returns: Set by the eBay seller; the eBay Money Back Guarantee covers an item that doesn't arrive or isn't as described.

    $4.58+ $8.79 shippingChecked Nov 8
    Visit eBay

Store links may earn us a commission.

All 4 stores and price history →

Specs compared

SpecMaster Flow Foundation Vent CoverFrost King Foundation Vent Foam Plug
TypeAutomatic Foundation VentVent Plug
Vent TypeFoundation ventVent Plug
Depth11.13 cm13.25 in
Dimensions17.5 in x 9.25 in (actual)6-1/2 in. x 7-3/4 in.
Height8 in6.5 INH
Length9.25 in13.25 in
Width16 in7.75 in
MaterialResinFoam, Polystyrene
Typical RoomsCrawl spaceCrawl space
Intended UseVentilationWinter insulation
ApplicationFoundationCrawl space
UseVentilationInsulation, Increase comfort, Reduce the risk o…
Show all 29 specsShow fewer specs
SpecMaster Flow Foundation Vent CoverFrost King Foundation Vent Foam Plug
Installation LocationFoundationCrawl spaces
Installation TypeSnap-in installationPressure fit installation
Installation HighlightsSnap-in installationPressure fit installation with no tools required
Airflow Volume57 sq. in. (net free vent area)—
Power SourceNon-Powered—
Typical EnvironmentHomes with a foundation—
Mounting Hardware IncludedYes—
Control TypeAutomatic—
Filter Included

What reviewers say

Master Flow Foundation Vent Cover

Buyers say the covers install easily and solve crawl space problems, with quality matching what they expected. A few ran into installation friction around the hook hole, and one had a hook break while closing the flap.

What people mention
  • InstallationMixedMost say it snaps on easily, but some had to enlarge the hook hole first.
  • Build qualityMixedOwners call it high quality, though one hook broke while closing the flap.
  • PricePraisedBuyers say it costs much less than other sites.
  • Crawl space protectionPraisedOwners report it solved a crawl space problem and keeps out debris.

Frost King Foundation Vent Foam Plug

Owners who use these plugs describe them as a quick, low-cost way to shut cold air out of crawl spaces and keep pipes from freezing. Most praise the fit and tool-free install; complaints center on sizing and the foam's durability.

What people mention
  • FitMixedOwners say the plug fits common square vents well but can be snug or loose depending on the vent brand.
  • InstallationPraisedReviewers like that it pressure-fits by hand with no tools and comes out just as easily.
  • Draft blockingPraisedUsers report less cold air coming through foundation vents in winter.
  • DurabilityCriticisedSome owners say the foam tears or compresses after a few seasons of use.

Questions and answers

Which is better for keeping rodents out of a crawl space?
The Master Flow. Its included screen blocks insects and small rodents while still letting air through. The Frost King plug blocks everything only while it is in place.
Which lasts longer?
The Master Flow aluminum cover is built to stay mounted for years. The Frost King foam plug is a seasonal item that can compress and wear with repeated install and removal.
Can I use both together?
Not on the same vent. The Master Flow mounts over the vent opening, and the Frost King fills the opening, so they compete for the same space.
Is the Frost King plug worth stepping up to the Master Flow?
If you want year-round venting and rodent protection, yes. If you only need a winter seal and already have a screen, the plug does that job with less work.
Will the Master Flow fit my vent?
It fits standard 16 x 8 in. foundation vents. Measure the opening first; some owners had to enlarge the hook hole.
Does the Frost King plug stop frozen pipes?
It helps by sealing cold air out of the crawl space, which is its stated purpose. It does not insulate the pipes themselves.

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More comparisons

  • Recessed Crawl Space Vent Cover - Shallow Depth Encapsulation Seal vs Master Flow 7.4 in. H X 15.4 in. W Mill Aluminum Foundation Vent Cover
  • Recessed Crawl Space Vent Cover - Standard Depth Encapsulation Seal vs Master Flow 7.4 in. H X 15.4 in. W Mill Aluminum Foundation Vent Cover

Buying guides that pick them

  • Best insulated crawl space vent covers
Yes
—
Included AccessoriesScreen—
Heat SentryYes—
Fits vent size16" x 8" (406 mm x 203 mm)—
Package quantityPK2—
Covers per packageTwo (2) covers and springs per package—
Energy Efficiency—Reduce heating bills, Help reduce utility bills
Color—White
Shape—Square