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Design and sizing

Full Load Hours

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Category: Design and sizing

Plain-English definition: Full Load Hours describes part of the heating or cooling demand the geothermal system must satisfy. Accurate load information helps prevent comfort complaints, short cycling, unnecessary backup heat, and poor humidity control.

Whiteboard-style diagram for Full Load Hours showing room-by-room load, house floor plan, sizing, equipment selection, and loop sizing concepts.
This simplified diagram shows room-by-room load, house floor plan, sizing, equipment selection, and loop sizing concepts as it relates to Full Load Hours. Exact geothermal designs vary by home, site conditions, equipment selection, and local requirements.

What Full Load Hours means

Full Load Hours describes part of the heating or cooling demand the geothermal system must satisfy. Accurate load information helps prevent comfort complaints, short cycling, unnecessary backup heat, and poor humidity control.

In a homeowner proposal, full load hours should connect to a real part of the job: the indoor equipment, underground loop or water source, duct or hydronic distribution, controls, permitting, startup testing, or closeout paperwork. When the term appears without that connection, ask the contractor to point to the line item, drawing, calculation, model number, or checklist that explains it.

Why Full Load Hours matters for geothermal installation

Geothermal systems are sensitive to design details because the indoor equipment and the earth-side heat exchanger have to work as one system. Full Load Hours can affect comfort, reliability, efficiency, serviceability, or the way competing bids should be compared. A low bid that leaves the term undefined may not include the same design work, installation labor, testing, or documentation as a more complete bid.

Where homeowners may encounter it

  • Equipment schedules, proposal line items, and system-design summaries.
  • Installer conversations about load calculations, loop fields, wells, ductwork, hydronics, controls, or commissioning.
  • Permit notes, drilling or well records, startup checklists, warranty documents, and owner handoff packets.

Questions to ask your installer

  • How does full load hours apply to my house and site?
  • What calculation, test, drawing, equipment data, or permit supports the recommendation?
  • Who verifies it during installation or startup?
  • Will it appear in the final documentation I receive after commissioning?

Red flags to watch for

  • The proposal uses full load hours without explaining what it means for your home.
  • The installer cannot show who is responsible for design, installation, verification, or documentation.
  • Important assumptions are missing from the written quote, especially where site conditions, water, drilling, ducts, controls, or permits are involved.

Related glossary terms

Sources

  • Technical Manuals — ACCA. Used for Manual J, Manual D, Manual S, load, duct, and equipment-selection terminology.
  • Geothermal Heat Pumps — ENERGY STAR. Used for homeowner-facing geothermal equipment context.
  • IGSHPA — International Ground Source Heat Pump Association. Used for ground-source system design and installation terminology.

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