The Caleffi 108860A is a iStop anti-freeze valve with 1" Female NPT connections.
Best for outdoor or unheated piping runs where a freeze event would otherwise split the line.
Specifications sourced from Caleffi North America technical literature. Last reviewed July 2026.
Key Features
Built for Air-to-Water Heat Pumps
The iStop anti-freeze valve is intended for air-to-water hydronic heat pump installations, protecting the outdoor portion of the circuit if the unit stops during freezing weather.
Automatic Discharge Near Freezing
The valve opens and discharges a small volume of water as the medium approaches freezing, relieving the expansion that would otherwise split piping or the heat exchanger.
Install on Both Flow and Return
Caleffi specifies one valve on the flow line and one on the return, mounted outdoors close to the heat pump, vertical with the discharge pointing downward. Do not insulate the valve.
Union Connection for Service
A union tailpiece allows removal for inspection or replacement without disturbing the connected piping.
Technical Specifications
| Product Type | Anti-Freeze Valve |
| Connection Size | 1" |
| Connection Type | Female NPT |
| Series | iStop |
| Maximum operating pressure | 150 psi |
| Ambient temperature range | -22 - 140 deg F |
| Material | brass |
| Shipping Weight | 1.9 lb (approx.) |
Related Products
- Caleffi 108866A : iStop 1" Press
- Caleffi 108869A : iStop 1" Sweat
- Caleffi 108870A : iStop 1-1/4" Female NPT
- Caleffi 108876A : iStop 1-1/4" Press
Frequently Asked Questions
How does Caleffi 108860A protect against freezing?
The iStop anti-freeze valve opens and discharges a small volume of water as the medium approaches freezing. Relieving that volume prevents the ice expansion that would otherwise split piping or fittings.
What connection does Caleffi 108860A use?
It is supplied with 1" Female NPT connections. Other sizes and connection styles in the iStop range are listed under Related Products.
What are the pressure and temperature limits of Caleffi 108860A?
Maximum operating pressure is 150 psi.
What is the warranty on Caleffi 108860A?
Caleffi covers this product under its standard two-year limited warranty against defects in material and workmanship from the date of shipment. ZOT Supply is an authorized Caleffi distributor.
- Product Type:
- Anti-Freeze Valve
- Series:
- iStop
- Product Family:
- Anti-freeze Valves
- Connection Type:
- Female NPT
- Connection Size:
- 1 inch
- Max Operating Pressure:
- 150 psi