Double poly · inflation blower · not a kit

Double-layer greenhouse plastic / high tunnel inflation blower: air gap, outside air, ¼-inch pressure (sourced)

Growers search double-layer greenhouse plastic, high-tunnel inflation blower, and how to inflate two layers of 6-mil film after the house is up. This page is the inflation sibling — why an air gap, when a single layer is enough on an unheated Practice 325 tunnel, outside air versus inside air, lock channel, damper and manometer, light loss, and power. Winter heaters stay on how to heat a high tunnel; that page names double poly only in passing. Film sheets stay on high-tunnel plastic replacement. Lock channel stays on high-tunnel wiggle wire. It is not a commercially manufactured high-tunnel kit and not a USDA payment schedule.

Extension quotes copied 15 October 2026, about 03:30 UTC from MSU Biernbaum 2013, Bartok (UConn) 2013, e-GRO Owen (OSU) 2025, UF/IFAS HS1466, Penn State, N.C. State, and Johnny's. Featured Amazon prices copied the same night. A missing featured price stays an em dash. Ratings are not copied. Seller inside-air or “NRCS eligible” claims stay labeled. EQIP language below is the structure-only wording already on what EQIP will not pay for. Second film, blowers, tape, a manometer, and site electricity are grower expense. No USDA payment dollar is invented here.

Kit index: commercially manufactured kits. Replacement-parts directory: high-tunnel replacement parts. Size map: high-tunnel sizes. Film: 6-mil plastic replacement. Torn film / poly-patch: plastic repair tape. Lock channel: wiggle wire. End walls: high-tunnel end walls. Ventilation: high-tunnel ventilation fans. Winter heat: how to heat a high tunnel. County inspection: EQIP checklist.

Why two layers, and why an air gap

A second 6-mil sheet is not decoration. Land-grant pages treat the inflated air space as insulation, a tighter cover in wind, and a condensation buffer — on a greenhouse. A high tunnel is usually still a single-layer season-extension house.

One of the differentiating factors between the various names is whether the structure is covered with a single layer of polyethylene film (high tunnel) or two layers with an electric inflation fan keeping the two layers separate for greater insulation as well as a tighter covering less prone to move about in the wind (hoophouse or greenhouse).

Source: Michigan State University — John Biernbaum, High Tunnel / Hoophouse / Solar Greenhouse notes (2013).

With heated greenhouse, the second inflated layer is generally reported to decrease heating requirement by 40%. If any heating at all will be used in the structure, even if only minimal heat on very cold nights, a double inflated layer is necessary.

Source: Michigan State University — John Biernbaum, High Tunnel / Hoophouse / Solar Greenhouse notes (2013). The 40 percent figure is 2013 Biernbaum copy, not a current energy audit.

Where we have such a large emphasis on winter production, we have decided to go with the second layer in most cases. We have two greenhouses with the double layer. The plastic does not blow and flap under windy conditions and there is an approximately 4F advantage or increase on average under cold and freezing conditions.

Source: Michigan State University — John Biernbaum, High Tunnel / Hoophouse / Solar Greenhouse notes (2013). Qualitative 4F observation — not an invented soil °F table.

Two layers of 6 mil are the standard. It saves 35 percent on heating costs as opposed to a single layer. When inflated, it keeps the plastic tight, reducing stress on the connections. It reduces condensation, as the inner layer is warmer. It also provides a level of insurance should one layer tear.

Source: John W. Bartok Jr. (University of Connecticut, emeritus) — Greenhouse glazing tips, Greenhouse Management (published 5 March 2013). Bartok's 35 percent and MSU's 40 percent stay labeled separately. This page does not average them.

This air layer between the two layers of poly film helps reduce heat loss, minimizes condensation, and improves the structure's ability to withstand wind and snow loads.

Source: e-GRO Alert 14-05 — W. Garrett Owen, The Ohio State University, Proper Installation & Maintenance of a Double-Poly Greenhouse Inflation Blower (February 2025).

Single layer on an unheated Practice 325 tunnel

Practice 325 is still an unheated season-extension structure unless the county writes something else. Double poly is the greenhouse covering. Heaters, if any, stay on how to heat a high tunnel.

High tunnels are generally covered with a single layer of greenhouse-grade polyethylene film (six mil) instead of the air-inflated double polyethylene layer found in greenhouses.

Source: Penn State Extension — High Tunnel Production (updated 13 March 2023).

A single layer will provide significant crop protection and is what is most common in hightunnel or hoophouse production.

Source: Michigan State University — John Biernbaum, High Tunnel / Hoophouse / Solar Greenhouse notes (2013).

One layer may be adequate for high tunnels covered for season extension in the spring. This also works fine for nursery narrow overwintering hoophouses.

Source: John W. Bartok Jr. (University of Connecticut, emeritus) — Greenhouse glazing tips, Greenhouse Management (published 5 March 2013).

A high tunnel, or hoophouse, is basically an arched or hoop-shaped frame covered with clear plastic and high enough to stand in or drive a tractor through. Traditional high tunnels are completely solar-heated, without electricity for automated ventilation or heating systems.

Source: NC State Extension Growing Small Farms — Season Extension: Introduction and Basic Principles.

Hoophouses don't need electricity or heating systems, although some growers do add them to extend the season even further. In general, though, roll-up or roll-down sides are used to ventilate a hoophouse, and the sun does the work of heating it.

Source: Johnny's Selected Seeds — Protect Your Crops • Basic High & Low Tunnel Components (Byczynski / Johnny's Research Team).

Unlike regular greenhouses, high tunnel structures provide less environmental control and may not have electrical service, automated ventilation, or permanent heating systems (Lamont 2009).

Source: UF/IFAS Extension — Tian, Vincent, Gong, Zhao, and Agehara, Using High Tunnels to Enhance Organic Vegetable Production in Florida: an Overview (HS1466).

Hoop houses are not typically built to be environmentally controlled. They are meant to be a season extender, not a four-season greenhouse. The double-layer improves this, but only enough to help improve the growing environment into the shoulder seasons.

Source: Bootstrap Farmer — Double Layer Inflation Kits (manufacturer blog; opened 15 October 2026). Manufacturer copy — not a land-grant yield.

An alternative to using an inflation blower is the use of greenhouse spacer blocks. Using spacer blocks can be particularly useful for smaller structures or in situations where running an electric blower continuously is not feasible. Spacer blocks offer a passive solution that doesn't require electricity, potentially reducing operating costs. However, they may not provide the same level of consistent inflation as a blower system, especially in larger greenhouses.

Source: e-GRO Alert 14-05 — W. Garrett Owen, The Ohio State University, Proper Installation & Maintenance of a Double-Poly Greenhouse Inflation Blower (February 2025). Passive spacer blocks are a no-electricity alternative, not a blower.

How inflation works: blower, outside air, damper, pressure

The blower is a small continuous fan holding pressure between two sheets — not a ventilation fan. Summer air exchange stays on high-tunnel ventilation fans.

When installing an inflation blower, it is important to select a fan with sufficient cubic feet per minute (CFM) capacity to evenly inflate the size of your greenhouse. I have seen 50, 60, 77, and 148 CFM inflation blowers available from various greenhouse manufacturers and supply companies.

Source: e-GRO Alert 14-05 — W. Garrett Owen, The Ohio State University, Proper Installation & Maintenance of a Double-Poly Greenhouse Inflation Blower (February 2025). Sizes seen in the trade — not a 30×96 shopping list.

Once the inflation blower is selected, mount the blower on the interior of the structure. In most free-standing greenhouses, inflation blowers are typically mounted on the first or second bow from an end wall; however, mounting will vary based on greenhouse manufacturers and space. Additionally, inflation blowers are often manufactured with a damper which is used to control airflow and prevent overinflation and damage the glazing material.

Source: e-GRO Alert 14-05 — W. Garrett Owen, The Ohio State University, Proper Installation & Maintenance of a Double-Poly Greenhouse Inflation Blower (February 2025).

A critical aspect of the installation process is ensuring that the inflation blower draws in outdoor air rather than greenhouse air. Using outdoor air prevents moisture from being introduced between the two layers of poly. If greenhouse air is used, its higher humidity levels can lead to condensation forming between the layers. This condensation reduces light transmission, accelerates poly degradation, and creates an environment conducive to mold growth.

Source: e-GRO Alert 14-05 — W. Garrett Owen, The Ohio State University, Proper Installation & Maintenance of a Double-Poly Greenhouse Inflation Blower (February 2025).

If the plastic has been installed properly without any leaks or holes, there is very little air blown between the layers once it is inflated. The blower is just holding the pressure similarly to the way you would blow up and hold a balloon. Under this situation, where the air comes from is not critical. But a batten may loosen slightly, or the plastic may get punctured with a few small holes. Then there is air exchange, and the drier outside air reduces the potential for moisture condensation. I have been in greenhouses where several inches of water collected between the layers.

Source: John W. Bartok Jr. (University of Connecticut, emeritus) — Greenhouse glazing tips, Greenhouse Management (published 5 March 2013).

Once installed, the fan should operate continuously, 24/7, to maintain consistent inflation pressure. This ensures proper insulation and structural integrity while preventing deflation during periods of high wind or snow.

Source: e-GRO Alert 14-05 — W. Garrett Owen, The Ohio State University, Proper Installation & Maintenance of a Double-Poly Greenhouse Inflation Blower (February 2025). Outage means the bubble deflates.

The research that Professor Bill Roberts at Rutgers University did when he first introduced the inflated double layer concept showed that ¼ inch was an optimum pressure. Going below this level will allow the plastic to ripple on windy days, putting stress on the endwall battens. This can lead to tears. Overinflating tends to stretch the plastic. Use a homemade or commercial manometer to measure the pressure. Adjustment is made by opening or closing the intake on the inflation blower or adjusting the motor speed with a rheostat.

Source: John W. Bartok Jr. (University of Connecticut, emeritus) — Greenhouse glazing tips, Greenhouse Management (published 5 March 2013), citing Rutgers Professor Bill Roberts. ¼ inch of static pressure is not Bootstrap Farmer's vendor “inflate 6–8 inches” gap.

The difference between 1.5 inches and 6 inches of space adds about 1 percent to the total heat loss.

Source: John W. Bartok Jr. (University of Connecticut, emeritus) — Greenhouse glazing tips, Greenhouse Management (published 5 March 2013).

I’ve seen where vinyl drier vent hose was used and UV light deteriorated the hose, thus inflating the double-poly with greenhouse air resulting in condensation.

Source: e-GRO Alert 14-05 — W. Garrett Owen, The Ohio State University, Proper Installation & Maintenance of a Double-Poly Greenhouse Inflation Blower (February 2025).

With double layer film and air inflation, electricity is necessary for the blower. Power lines can be placed in the same trench as the water line. I have heard of people using a solar powered blower, but it is rare at this point in time. I read that the annual cost of running the inflation blower for one greenhouse is only about $5.

Source: Michigan State University — John Biernbaum, High Tunnel / Hoophouse / Solar Greenhouse notes (2013). The “about $5” annual cost is 2013 “I read that” copy — not a current utility bill.

Two sheets in the same lock channel

Both layers are greenhouse-grade 6-mil film. Channel and spring-wire featured prices stay on high-tunnel wiggle wire. Intake through an end wall is an end-wall cut, not a kit door — see high-tunnel end walls.

The second layer of plastic is installed with lock channel and spring wire. When adding the second layer of plastic, the second layer only needs to cover the top of the hoop house down to the hip boards to provide benefits. Install the plastic into the existing lock channel with additional spring wire.

Source: Bootstrap Farmer — Double Layer Inflation Kits (manufacturer blog; opened 15 October 2026). Manufacturer install notes — not a land-grant channel count.

We recommend that both layers of the greenhouse film are 6 mil., as a thinner plastic may not hold up as well with the installation of an inflation kit.

Source: Bootstrap Farmer — Double Layer Inflation Kits (manufacturer blog; opened 15 October 2026).

The standard film thickness is 6 mil (0.006 inch) and the most common types last for 3 to 4 years.

Source: Michigan State University — John Biernbaum, High Tunnel / Hoophouse / Solar Greenhouse notes (2013).

When using a polyethylene cover, a minimum 6-mil greenhouse grade, UV-resistant material is required.

Source: USDA NRCS Pennsylvania — Seasonal High Tunnel System for Crops. Cover grade, not a second-layer payment.

Light transmission trade-off

High tunnel frames are usually covered with one or two layers of polyethylene film (Kaiser and Ernst 2012); in the latter case, an inflated air layer exists in between the two layers (Figure 5). The double-layer roof provides better insulation and cold protection when installed with an inflation fan; but the two layers may reduce light penetration by about 3%–15% more than would a single layer of plastic (Maynard and O’Donnell 2018).

Source: UF/IFAS Extension — Tian, Vincent, Gong, Zhao, and Agehara, Using High Tunnels to Enhance Organic Vegetable Production in Florida: an Overview (HS1466), citing Maynard and O’Donnell 2018. The 3%–15% band is that citation — this page does not invent a PAR table.

Condensation between layers (inside-air inflation) cuts light further — e-GRO's outdoor-air warning above. Shade-cloth cooling is a different job and stays on the shade-cloth page.

Bootstrap Farmer air inflation kit (manufacturer, not Amazon)

Live Shopify JSON 15 October 2026, about 03:30 UTC. Kit frames stay on manufacturer product pages. No invented affiliate tag.

Source: Bootstrap Farmer — Greenhouse Air Inflation Kit (Shopify JSON opened 15 October 2026). Vendor notes on that page: Includes 60 cfm blower, exhaust air deflector, mounting bracket, 72" inlet air hose, inlet damper/air regulator;Operates at 110 volts, pulling 0.42 amps. Note: We recommend that you use air from the outside, which is less humid, reducing condensation. Note: This fan lacks a plug. Many growers hardwire them in, but a plug can easily be attached. Consult a licensed electrician if this is something you are not comfortable doing.

Sourced Amazon inflation parts

Titles and featured one-time prices were copied from live amazon.com product pages 15 October 2026, about 03:30 UTC. Kit frames stay on manufacturer product pages. 16×90 film (B07D22SZCQ) 403'd tonight and is not re-priced here — compare it on plastic replacement. Poly-Patch B00YOIE4T2 and inflation-kit B004JVM8EC had no featured offer.

EQIP pays for the structure, not the blower

A second poly layer, inflation blower, repair tape, manometer, and site electricity sit outside the High Tunnel System Initiative payment unless your county office writes them in. Confirm with your NRCS district conservationist. Tunnel Spec does not invent a dollar.

Under the High Tunnel System Initiative, financial assistance is provided only for the structure itself. Electricity, venting systems, lighting, etc. can be installed providing the additions meets manufacturer’s designs and specifications. However, the grower is responsible for those costs.

Source: USDA NRCS High Tunnel System Initiative FAQ (Updated November 2024; Oregon-branded).

Producers can install heating, ventilation, or electrical systems at their own expense.

Source: USDA NRCS Pennsylvania — Seasonal High Tunnel System for Crops. One state office page, not a national inflation payment.

The practice does not include greenhouses or low tunnel systems.

Source: NRCS Conservation Practice Standard 325 High Tunnel System. Double-poly greenhouses are the covering CPS 325 contrasts with a high tunnel.

For polyethylene covers, use a minimum 6-mil greenhouse grade, UV-resistant material.

Source: NRCS Conservation Practice Standard 325 High Tunnel System. Minimum 6-mil when polyethylene is used — not a second-layer dollar.

Rules vary; call your county NRCS office.

FAQ

Why put two layers of poly with an air gap on a high tunnel?

MSU Biernbaum 2013: two layers with an electric inflation fan keep the layers separate for greater insulation and a tighter covering less prone to move about in the wind; the second inflated layer is generally reported to decrease heating requirement by 40% on a heated greenhouse; the plastic does not blow and flap, with an approximately 4F advantage under cold conditions. Bartok (UConn, 2013): two layers of 6 mil save 35 percent on heating costs versus a single layer; inflation keeps the plastic tight; the warmer inner layer reduces condensation; a second layer is insurance if one tears. Those 40% and 35% figures are labeled 2013 sources — this page does not average them. e-GRO Owen (OSU, 2025): the air layer reduces heat loss, minimizes condensation, and improves the ability to withstand wind and snow loads.

Is double poly worth it on an unheated NRCS Practice 325 season-extension tunnel?

Penn State: high tunnels are generally covered with a single layer of six-mil greenhouse-grade polyethylene instead of the air-inflated double polyethylene layer found in greenhouses. MSU: a single layer will provide significant crop protection and is what is most common in high-tunnel or hoophouse production; a double inflated layer is necessary if any heating at all will be used. Bartok: one layer may be adequate for high tunnels covered for season extension in the spring. N.C. State: traditional high tunnels are completely solar-heated, without electricity for automated ventilation or heating systems. Johnny's: hoophouses don't need electricity or heating systems, although some growers add them. Bootstrap Farmer (vendor): hoop houses are meant to be a season extender, not a four-season greenhouse; the double layer helps into the shoulder seasons. UF/IFAS: high tunnels may not have electrical service. e-GRO names spacer blocks as a no-electricity alternative that may not match blower inflation on larger houses. This page does not invent a one-house rule.

Should the blower pull outside air or inside air?

e-GRO Owen: draw outdoor air, not greenhouse air; humid inside air causes condensation between layers, which reduces light, accelerates poly degradation, and can grow mold; install an external intake. Bartok: with a tight install there is little air exchange once inflated (balloon analogy); once there are leaks, drier outside air reduces condensation — he has seen several inches of water between layers. Bootstrap Farmer manufacturer copy recommends outside air because it is less humid. One Amazon blower listing (B097HT6P4Q) says it pulls air from inside the greenhouse — that is seller copy, not the land-grant method. e-GRO: do not use vinyl dryer vent hose that UV can destroy.

How do I install two layers in lock channel, and where does the blower go?

Bootstrap Farmer (manufacturer): the second layer is installed with lock channel and spring wire, typically down to the hip boards, into the existing channel with additional spring wire; both layers 6 mil. e-GRO: mount the blower on the interior, typically the first or second bow from an end wall; many blowers have a damper to prevent overinflation; run 24/7. Lock-channel featured prices stay on the wiggle-wire page. End-wall intake fittings sit with the end-wall page's hardware, not a duplicate. This page does not invent a staple or channel count for a 20×40 or 30×96.

What static pressure should I run, and how do I check it?

Bartok, citing Rutgers Professor Bill Roberts: ¼ inch was an optimum pressure; below that the plastic ripples in wind and stresses end-wall battens; overinflating stretches the plastic; measure with a homemade or commercial manometer; adjust the intake damper or motor speed. e-GRO: adjust damper settings to maintain inflation without over-stressing the film. Bootstrap Farmer vendor copy says inflate 6–8 inches and monitor with a manometer — that inch gap is vendor copy, not Bartok's ¼-inch static pressure. The two numbers are different measurements. This page does not invent a CFM shopping list beyond e-GRO's 50 / 60 / 77 / 148 CFM sizes seen in the trade.

Does EQIP pay for a second poly layer, an inflation blower, or the electricity?

Tunnel Spec does not invent eligibility or dollars. The High Tunnel System Initiative FAQ says financial assistance is provided only for the structure itself, and that electricity, venting systems, lighting, etc. can be installed if they meet manufacturer designs — the grower is responsible for those costs. The Pennsylvania seasonal high tunnel page says producers can install heating, ventilation, or electrical systems at their own expense. CPS 325 does not include greenhouses. PA and CPS 325 name a minimum 6-mil greenhouse-grade UV cover when polyethylene is used — a cover-grade sentence, not a double-poly payment. Inflation blowers, a second film layer, tape, a manometer, and site electricity sit with those grower costs. Confirm with your NRCS district conservationist. See what EQIP will not pay for.

Rules vary; call your county NRCS office. Tunnel Spec does not determine eligibility, payment rates, or inspection outcomes. Confirm double-poly inflation with your NRCS district conservationist. As an Amazon Associate, we earn from qualifying purchases.