HVAC
HVAC Refrigerant Charge Calculator
Estimate line set charge adjustment as a planning figure, alongside the manufacturer's charging procedure rather than instead of it.
Result
An estimate for ordering and planning only. The final charge is set by measurement, using superheat on a fixed-orifice system or subcooling on a TXV system, against the manufacturer's chart for that model. Charging by weight alone, or by pressure alone, is how systems end up over or undercharged.
Get a Free Business AuditWhat moves the number
- Line set length beyond the factory charge, which is what the adjustment covers.
- Line diameter, since volume rises sharply with size.
- Refrigerant type, because charge per unit length differs.
Where this one goes wrong
Charging by pressure alone or by weight alone without verifying with superheat or subcooling as the manufacturer specifies. Charge is verified against measured conditions, and an estimate is a starting point rather than a result.
Before you quote
- The manufacturer's charging procedure for that specific equipment.
- That the system has been evacuated properly before charging.
- Superheat or subcooling measured at stable operating conditions.
Questions
About this calculator
Does this replace the manufacturer's charging procedure?
No. It estimates the adjustment for line set length so you can plan how much refrigerant to carry. The final charge is verified by the method the manufacturer specifies for that equipment.
Why does refrigerant type matter?
Because charge per foot of line differs between refrigerants, and because handling, pressures and equipment compatibility differ too. They are not interchangeable.
What happens if the charge is slightly off?
Capacity and efficiency drop in both directions, and persistent overcharge or undercharge shortens compressor life. That is why it is verified against measurements rather than estimated and left.
The formula
total = factory charge + (line length - included length) x ounces per foot / 16
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How to use this calculator
- System size (tons) (tons). Enter your own figure; the page starts at 3 tons.
- Factory charge (lb). From the nameplate. It covers the unit plus a standard line set.
- Line set length (ft) (ft). Enter your own figure; the page starts at 35 ft.
- Length the factory charge covers (ft) (ft). Enter your own figure; the page starts at 15 ft.
- Liquid line size. Enter your own figure; the page starts at 3/8 inch (1.2 oz/ft).
The result updates as you type, so you can try a figure, see what it does to estimated total charge, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| System size (tons) | 3 tons |
| Factory charge | 6.5 lb |
| Line set length (ft) | 35 ft |
| Length the factory charge covers (ft) | 15 ft |
| Liquid line size | 3/8 inch (1.2 oz/ft) |
What comes out
| Result | Value |
|---|---|
| Estimated total charge main result | 8.0 |
| Added for the extra line | 1.5 |
| Line beyond the factory allowance | 20 |
| Extra charge in ounces | 24 |
About 8.0 lb in total: the 6.5 lb factory charge plus 1.5 lb for the 20 feet of extra line.
How sensitive the answer is
Holding everything else steady and changing only system size (tons), this is what happens to estimated total charge. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| System size (tons) (tons) | Estimated total charge |
|---|---|
| 1.5 tons | 8.0 |
| 2.25 tons | 8.0 |
| 3 tons example above | 8.0 |
| 4.5 tons | 8.0 |
| 6 tons | 8.0 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- System size (tons) (tons)
- Measured in tons, starting at 3 tons.
- Factory charge (lb)
- From the nameplate. It covers the unit plus a standard line set.
- Line set length (ft) (ft)
- Measured in ft, between 0 and 300, starting at 35 ft.
- Length the factory charge covers (ft) (ft)
- Measured in ft, between 0 and 100, starting at 15 ft.
- Liquid line size
- Choose from 1/4 inch (0.6 oz/ft), 5/16 inch (1.2 oz/ft), 3/8 inch (1.2 oz/ft), 1/2 inch (2.1 oz/ft).
What the results tell you
| Result | What it is |
|---|---|
| Estimated total charge | The headline result. A decimal figure. |
| Added for the extra line | A decimal figure. |
| Line beyond the factory allowance | A number. |
| Extra charge in ounces | A number. |
Before you rely on this number
Sizing, capacity and load figures here are planning estimates. A real installation depends on the manufacturer's data for the specific equipment, the duct system it is going into, and a proper load calculation for the building. Use this to sanity-check a number or price a job, not to select equipment.
Estimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.