A heater install goes wrong in the first hour and costs you for the next fifteen years. The hardware is straightforward. The clearances, plumbing sequence, venting, and wiring are where the failures hide. ANSI Z223.1 sets the baseline for gas heater installation; the heat pump and solar manuals are the baseline for those. Read them. What follows is the field-level checklist we use on every new install.
Placement on the pad
- Five feet from any spa wall unless separated by a permanent barrier (fence, masonry wall). ANSI sets that minimum for gas heaters.
- Non-combustible base— concrete pad, brick, or hollow masonry topped with 4" and 24-gauge sheet metal. Never mount directly on wood or composite decking.
- Three feet of clear space on all service sides, minimum. Some manufacturers require more; the service manual wins.
- Wind protectionfor gas heaters exposed to steady wind — either set back three feet from the nearest wall or build a windbreak. High wind dilutes combustion air and causes intermittent ignition faults.
- Not under an overhanging roof for gas heaters. Combustion exhaust needs to dissipate; soffits trap it.
Plumbing sequence
The order of equipment on the return line is not optional. The correct sequence for any heater:
- Pump →
- Filter →
- Heater →
- Chemical feeder / salt cell →
- Pool returns
Why: the heater should see already-filtered water (no debris baking onto the heat exchanger) and should never see a high-concentration chemical feed (concentrated chlorine or acid corrodes the exchanger fast). A check valve between the heater and any downstream feeder prevents back-siphon during pump-off.
Thermal break on the return
Every gas heater and most heat pumps require a thermal break — typically 18–24 inches of metal or CPVC on the heater outlet before the Schedule 40 PVC picks back up. The brass or stainless nipple bleeds off residual heat so plain PVC never sees water above its service temperature. Skip this and the PVC union at the first tee softens, sags, and leaks in year two.
Gas line and venting (gas heaters)
- Size the gas line for the heater's peak BTU demand. A 400k BTU/hr heater on a line sized for 200k starves, runs rich, and fault-codes.
- Every gas heater gets a dedicated shut-off valve within six feet, a sediment trap on the inlet, and a gas pressure test at commissioning.
- Outdoor gas heaters are direct vent — combustion air is drawn from the sides and exhaust rises straight up. Keep the top clear.
- Indoor installation is a separate and more demanding category. Always a Category III or IV flue, always engineered combustion air, always by a licensed professional.
Electrical for heat pumps
- Dedicated 240V circuit, sized to the manufacturer's minimum circuit amperage. Common residential heat pumps draw 20–50 amps.
- Breaker per the nameplate. Under-breakering will nuisance-trip under startup load.
- Bonding wire— Florida code (NEC 680) requires all metallic pool equipment to be bonded back to the equipotential bonding grid. Not the same as grounding. Inspectors check this.
Fireman switch (gas heater protection)
Every gas heater downstream of a time-clocked pump needs a fireman switch — a low-voltage interlock that kills the heater a few minutes before the pump shuts off, so residual heat can dissipate through the exchanger instead of boiling in place. For millivolt heaters, the wire run from timer to heater must stay under 30 feet or the resistance drops the signal below the gas-valve holding current.
Every install we do gets a labeled equipment diagram taped inside the pool room or access panel. The next tech will thank you. So will you, in three years, when something fails and you've forgotten how it's wired.