Collectors: Hold ±1 to 2% RH With Backup Power for Humidors

A dedicated standby generator paired with an automatic transfer switch, a battery backed UPS for controls, and a load shedding sequence that protects humidity before anything else is the practical, code aware way to shield premium walk in humidors from irreversible damage. Before specifying equipment, we recommend a critical load audit with your MEP contractor, careful attention to generator siting and exhaust clearances, and alignment with NFPA 110 transfer expectations.

TL;DR:

• Prioritize humidity because humidifier output stops immediately during outages, while temperature drifts more slowly; a 65% to 72% relative humidity environment can slide toward danger.
• Size generators from peak loads, not steady wattage: compressors and fan motors may draw three to five times rated current briefly when starting.
• Use a separate UPS for controllers and sensors; many designs target transfer under ten seconds, and HVAC loads require separate capacity calculations.
• Modeling found that generators placed within roughly 15 to 25 feet of openings may allow carbon monoxide entry; greater clearance and vertical exhaust reduce risk.
• Witness commissioning under real failure conditions, including utility loss, sensor dropout, and transfer switch misfires, before storing a collection in the room.

Table of Contents

• What has to stay powered, and which systems can do it
• Sizing your generator and battery capacity for real run-time
• Keeping controls online so the system doesn’t fail itself
• The safety and code checklist no installer should skip
• From audit to commissioning: the implementation sequence
• How we build backup power into every bespoke humidor
• Three priorities I insist on for every commissioning
• Let us design your backup power into the humidor itself
• FAQ
• Sources

What has to stay powered, and which systems can do it

A walk in humidor is a perfectly balanced ecosystem, and relative humidity is the variable that collapses fastest when power fails. Temperature drifts slowly inside an insulated room, but humidifier output stops the instant current is lost, and within a short window a 65% to 72% RH environment can begin sliding toward the danger zone where mold and tobacco beetle activity accelerate. That is why humidity, not temperature, is the load you protect first.

The circuits that matter most during an outage are narrow and specific:

• Humidifier control boards and the misting or steam generation unit itself
• The precision compressor, air handler, or mini split that manages sensible cooling
• Monitoring, data logging, and alarm systems that alert staff to drift
• Small ventilation and safety fans required for even air distribution

Three solution categories cover nearly every bespoke installation. A standby generator, whether natural gas or diesel, supplies sustained power for outages measured in hours or days. A UPS or battery energy storage hybrid bridges the gap during transfer and can ride through brief interruptions without a generator ever starting. Combined heat and power systems suit larger facilities such as lounges or clubs with continuous thermal and electrical demand, offering steady output when designed for islanding, according to DOE guidance on CHP reliability. For most private collections, a generator and UPS pairing delivers the reliability needed without the complexity of a CHP build.

Sizing your generator and battery capacity for real run-time

Sizing starts with nameplate data, not guesswork. Add the running wattage of every critical circuit, then account for motor start inrush, since compressors and fan motors can draw three to five times their rated current for a few seconds at startup. That inrush figure, not the steady state load, often determines whether a generator sized “on paper” actually holds voltage when equipment cycles on.

1. List every critical load’s rated kW and its motor start multiplier
2. Sum the peak kW to size generator capacity with margin
3. Multiply average running kW by expected outage hours to estimate kWh demand
4. Match fuel storage or utility gas capacity to that kWh target
5. Add a UPS sized for controls and sensors, calculated separately from HVAC load

Short outages measured in minutes to a few hours favor a UPS or BESS that can carry the full humidor load without the generator ever firing. Multi-day outages demand fuel logistics: natural gas offers continuous supply with lower emissions where a utility line exists, while diesel or propane require on-site storage and a refueling plan. Hybridizing a smaller generator with battery storage, as DOE guidance suggests, lowers fuel logistics while improving response during the transfer window.

Pro Tip: Size your generator against motor start inrush, not steady state wattage. An undersized unit that trips on startup never gets the chance to protect your humidity at all.

Keeping controls online so the system doesn’t fail itself

Generators and batteries only matter if the control layer survives the transition between them. A UPS dedicated to controllers and sensors, separate from the HVAC power path, holds setpoints steady during the automatic transfer switch’s brief window, which emergency system expectations generally place under ten seconds, according to NFPA 110 and NFPA 70 transfer standards.

NFPA 110 and NFPA 70 define transfer timing expectations for emergency and legally required standby systems, including automatic transfer switch performance, which is the backbone of a code aware backup design.

Beyond transfer timing, control redundancy deserves its own design pass:

• Run PID control loops with multiple alarm thresholds rather than a single setpoint trigger
• Install a secondary sensor path, battery backed and wireless or hardwired, independent of the primary controller
• Confirm that communication repeaters carry their own battery backup, since a wireless sensor network without one becomes a single point of failure
• Commission failure scenarios deliberately: pull a sensor, drop communication, and force an ATS mis-transfer to document fail-safe behavior

A humidor that holds ±1 to 2% RH under normal conditions can still swing wildly if the controller loses its mind during a power event rather than the compressor losing its motor. Testing the control logic, not just the generator, is what separates a resilient installation from an expensive one that fails anyway.

The safety and code checklist no installer should skip

Generator siting carries real risk, and the rules exist because people have been hurt. CDC and NIOSH guidance on carbon monoxide documents that many generator related CO incidents trace back to exhaust placed too close to windows, doors, or air intakes. Modeling cited in a NIST and CDC study on generator CO entry found that placement under roughly 15 to 25 feet from openings can allow carbon monoxide entry in many scenarios, and that greater clearance combined with elevated or vertical exhaust stacks meaningfully reduces that risk.

A short list of checks belongs on every project schedule before equipment arrives:

• Confirm exhaust and fresh air intake separation against CDC and NIOSH clearance guidance
• Verify transfer switch classification and timing against NFPA 110 and NFPA 70
• Document fuel tank placement, flood elevation, and environmental best practices as outlined in FEMA P-1019
• Secure permits before trenching, tank placement, or electrical tie-ins begin

FEMA P-1019 recommends that critical facilities identify their essential functions first and size standby power to match those loads, a sequence that keeps permitting straightforward because the scope is defined before equipment is ordered.

From audit to commissioning: the implementation sequence

A bespoke walk in humidor backup project moves through a predictable sequence, and skipping a step almost always shows up later as a change order.

1. Conduct a critical load audit and set minimum acceptable humidity and temperature thresholds for the space
2. Draft an electrical one-line diagram specifying ATS and UPS capacity, generator size, and fuel logistics
3. Secure permits, confirm exhaust siting, and prepare the site with environmental best management practices
4. Install and witness commission every failure scenario: utility loss, ATS transfer, sensor dropout, and generator start
5. Establish remote monitoring and a documented maintenance and fuel refresh schedule

The backup humidor readiness steps for cigar collectors we have outlined separately walk through the collector facing version of this checklist in more detail. For HVAC specific guidance on precision humidity equipment feeding into this design, our piece on holding ±1 to 2% RH with DOAS or desiccant systems covers the equipment side that the electrical plan must support. Witnessed commissioning matters more than any single component spec. An ATS that transfers too slowly, or recloses without control, can create a transient that shocks the humidity system even when every other piece of equipment is correctly sized.

How we build backup power into every bespoke humidor

We offer custom walk in humidors designed to hold optimal humidity for collectors, lounges, and clubs who cannot afford a single lapse in climate control. Every custom installation we design accounts for the electrical and controls layer from the first consultation, not as an afterthought once the cabinetry is finished.

Our walk in humidors are tailored to aesthetic and functional requirements, including integration of backup power, monitoring, and failover into the finished room. Delivery and consultation ensure the electrical plan, humidity strategy, and finish carpentry are coordinated as one system rather than by separate vendors working independently. Experience with collectors and lounge owners has informed the sequencing of generator, UPS, and control redundancy into a coherent installation, with commissioning results documented as requested.

Three priorities I insist on for every commissioning

Protect humidity first. Every load shedding sequence, every generator size calculation, and every UPS specification should exist to serve that single priority, because RH punishes you in days while temperature drift takes weeks.

Require witnessed commissioning, not a paper spec. I have seen beautifully engineered one-line diagrams fail in the field because nobody forced an ATS transfer under load before the client moved their cigars in.

Insist on a documented maintenance and fuel logistics plan before the generator is ever delivered. An undersized genset or a sensor network with no battery backed path are the two mistakes that turn an elegant design into an expensive lesson.

— Belle Dunn

Let us design your backup power into the humidor itself

We treat backup power as part of the humidor, not an add-on bolted in after the cabinetry ships. Starting with Dunn’s Bespoke, our consultation walks through your critical load audit, generator and UPS sizing, and the controls redundancy that keeps your collection safe during transfer.

If a full custom walk in build is not yet the right step, our electronic humidor lines offer a strong starting point for collections that need precision climate control without a ground-up installation.

• Explore our Humidor Supreme 9200 Series Double-Door Electronic Humidor for a dual-zone, high-capacity option
• Compare the Humidor Supreme 9000 Series and 9100 Black for single-zone electronic protection
• Browse our full Electronic Humidors and Cabinet Humidors collections

Request a consultation through Dunn’s Bespoke and we will talk through financing, installation support, and the backup power architecture your collection deserves.

FAQ

What size generator do I need for a walk in humidor?

Size is determined by adding the peak kW of every critical load, including motor start inrush that can run three to five times a compressor’s rated current, then adding margin. A critical load audit following FEMA’s approach to critical facility power planning is the right starting point before any equipment is ordered.

How far should a generator exhaust be from windows or doors?

CDC and NIOSH guidance calls for siting generator exhaust well away from windows, doors, and air intakes to prevent carbon monoxide entry. Modeling in a NIST and CDC study found that clearances of roughly 15 to 25 feet, combined with vertical exhaust stacks, meaningfully reduce CO risk compared to closer placement.

How fast does the transfer switch need to work?

NFPA 110 and NFPA 70 outline transfer timing expectations for emergency and legally required standby systems, and many designs target transfer in under ten seconds to keep controllers and sensors from losing power. A UPS dedicated to the control layer bridges that window regardless of how quickly the ATS completes its switch.

Does Dunn’s install backup power systems directly?

We design bespoke walk in humidors with backup power, controls redundancy, and monitoring integrated from the first consultation through Dunn’s Bespoke. Pricing for a bespoke project is available on request once your critical load audit and site details are reviewed.

What’s the biggest mistake collectors make with backup power?

The most common error is sizing a generator against steady state wattage while ignoring motor start inrush, which causes the unit to trip the moment equipment cycles on. A close second is skipping witnessed commissioning, which means failure scenarios like sensor dropout or ATS mis-transfer never get tested until they happen for real.

Sources

• CDC / NIOSH guidance on carbon monoxide and generators
• FEMA P-1019 Emergency Power Systems for Critical Facilities
• DOE / CHP and back-up power guidance

Recommended

• ±1–2% vs ±5–10%: What Collectors Need for Cigar Humidification
• Collectors: 5 Precise Checks When Your Humidor Won’t Hold Humidity
• 65–68% RH: How Collectors Keep Cigar Lockers Stable and Mold Free
• Why Precise Humidity Control Matters for Cigar Collectors