Infiltration

Category: Design and sizing

Plain-English definition: Infiltration is a design value used to match the geothermal equipment, ground loop, pumping, controls, and indoor distribution to the actual house. Homeowners should ask where the value came from and whether it is documented in the proposal.

What Infiltration means

Infiltration is a design value used to match the geothermal equipment, ground loop, pumping, controls, and indoor distribution to the actual house. Homeowners should ask where the value came from and whether it is documented in the proposal.

In a homeowner proposal, infiltration 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 Infiltration 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. Infiltration 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.

How Infiltration affects the project scope

For a core geothermal concept, the important question is how the installer turns the concept into a documented design choice. Ask whether infiltration affects equipment capacity, loop length or well requirements, pump selection, controls, duct or hydronic work, permits, startup readings, or future service access. Strong proposals make those connections visible instead of leaving homeowners to guess what is included.

Before signing, compare how each bidder explains infiltration. A better proposal usually names the calculation, drawing, test, model number, permit, or commissioning step that supports the recommendation. If the answer is only verbal, ask for written documentation before treating the quote as complete.

Also ask what would change if the field conditions differ from the first assumption. A loop can encounter wetter or drier soil than expected, a bore can hit different rock or water zones, an older duct system can restrict airflow, and a control setting can change when backup heat starts. A homeowner-friendly installer will explain how infiltration is checked during design and then verified after installation, so the final system is not just sold correctly but actually handed over with usable evidence.

For core glossary items, request a simple closeout record. It does not need to be a complex engineering package for every house, but it should be detailed enough for a future service technician to understand what was installed, what readings were recorded, and why the design choices were made. If the installer cannot explain how this item will be verified, documented, or serviced later, treat that as a proposal-quality concern rather than a vocabulary problem.

That record protects the homeowner because it turns a sales conversation into a serviceable system history.

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 infiltration 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 infiltration 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

• Geothermal Heat Pump
• Ground-Source Heat Pump
• Sensible Load
• Building Envelope
• Air Leakage
• Room By Room Load Calculation

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.