Quick answer
For a pool under 5,000-6,500 gallons, a full-size 240V heat pump is usually overkill on install cost — the FibroPool FH120 (20,000 BTU, about $1,999) is the best pick if you want real continuous heating without running new electrical, since it plugs into a standard 120V outlet instead of the 240V circuit every other heat pump on this site needs. The AQUASTRONG 16,000-18,000 BTU heat pump (120V, roughly $900-$1,800 depending on retailer) undercuts it on price if you’re comfortable with a newer budget-import brand. For the cheapest possible boost with zero electrical work, two or three Intex 28685E Solar Mats (about $30-$37 each) add 5-9°F on sunny days per Intex’s own spec, though they do nothing after dark.
A small pool — a soft-side above-ground pool, a cocktail pool, or a spa-adjacent setup under about 5,000-6,500 gallons — creates a specific problem the rest of this site’s size guides don’t solve: our 10,000-gallon guide already starts at the point where a standard 240V heat pump like the FibroPool FH255 makes sense, but running a new 240V circuit (double-pole breaker, dedicated line, often an electrician) can cost more than the heater itself on a pool this small. The 120V plug-in heat pump category exists specifically to skip that cost, even though it means accepting lower BTU output than you’d get from a 240V unit at the same price.
Best pool heaters for a small pool at a glance
| Heater | Power | BTU | Best for | Price |
|---|---|---|---|---|
| FibroPool FH120 | 120V (standard outlet) | 20,000 | No electrician, established brand | ~$1,999 |
| AQUASTRONG 16K/18K | 120V (standard outlet) | 16,000-18,000 | Lowest cost, heat + cool | ~$900-$1,800 |
| Intex 28685E Solar Mat | None (solar) | N/A (+5-9°F/sunny day) | Cheapest, zero electrical | ~$30-$37/panel |
1. FibroPool FH120 — Best for No Electrician Required
FibroPool FH120 Heat Pump (20,000 BTU, 120V)
- Plugs into a standard 120V outlet or heavy-duty extension cord — no dedicated 240V circuit, double-pole breaker, or electrician visit, unlike FibroPool's own larger FH255 and every other heat pump covered on this site.
- 20,000 BTU sits just under the strict 25,000-BTU floor the 5-BTU-per-gallon rule would call for on a full 5,000-gallon pool, but it's FibroPool's own rated ceiling for that size — expect a slower rise near the top of the range rather than a unit that simply can't keep up.
- Genuinely counterintuitive pricing: at about $1,999, the FH120 costs more than FibroPool's own 55,000-BTU FH255 (roughly $1,799, our pick for 10,000-gallon pools) despite putting out less than half the heat — the 120V convenience itself is the expensive part, not the BTU output.
- Best fit for renters, seasonal setups, or anyone who doesn't want to commit to permanent 240V wiring for a pool that might move or get replaced.
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If the choice is between paying an electrician for a 240V line or paying FibroPool’s premium for a plug-and-play 120V unit, the FH120 is the established-brand answer. It won’t out-heat a 240V pump, but it’s the only FibroPool model that skips the wiring project entirely.
2. AQUASTRONG 16,000-18,000 BTU — Best Budget Pick
AQUASTRONG Heat Pump (16,000-18,000 BTU, 120V)
- Same 120V plug-in category as the FH120, but priced well below it on most retailer listings — though the spread is wide ($699-$1,800 seen across different listings/sites), so check the actual checkout price before assuming the lowest figure applies.
- 5.5 COP and a titanium heat exchanger on paper match mid-tier 240V heat pumps, but AQUASTRONG doesn't have the decade-plus track record FibroPool, Hayward, or Pentair have on this site's other picks.
- Dual heating and cooling mode — useful if the small pool is in a hot climate and occasionally needs cooling down rather than warming up, a feature the FH120 doesn't offer.
- Fits the same "budget-import" tier this site has flagged before on big-box retailer listings — a real option, but go in knowing the brand doesn't have an established service network if something fails outside the 3-year warranty.
For the tightest budget, AQUASTRONG undercuts the FH120 while staying in the same no-electrician 120V category. The tradeoff is brand history, not the core spec sheet.
3. Intex 28685E Solar Mat — Cheapest, Zero Electrical Work
Intex 28685E Solar Mat
- No power draw, no circuit, no installation beyond connecting it inline with the pump hose — the lowest-cost and lowest-effort option on this list by a wide margin.
- Multiple panels link together for more surface area, the same approach covered in more depth in our Intex pool heater guide and best solar pool heater picks.
- Only adds heat while the sun is out and the pool pump is running — it can't hold a set temperature overnight or on cloudy days the way either heat pump above can.
- Makes the most sense paired with a pool cover to hold the gain overnight, or as a free supplement stacked on top of a small heat pump rather than a standalone heating solution.
If the pool only needs a few extra degrees on sunny days and running a heat pump (even a 120V one) feels like overkill, a stack of solar mats is the cheapest way to get there — just don’t expect it to replace a real heater once fall cools off the afternoons.
Why not just use a resistance heater?
Electric resistance heaters — covered in full in our best electric pool heater guide — are also 120V/240V options built for small pools and spas, and the budget EcoSmart Smart Spa 11 (~$499) is cheaper upfront than either heat pump here. The tradeoff is running cost: a resistance heater delivers exactly 1 unit of heat per unit of electricity, while the FH120 and AQUASTRONG’s heat-pump compressors move several units of heat per unit of electricity drawn, so they cost less to run all season even though they cost more to buy. Pick a resistance heater for occasional/backup use, and a 120V heat pump if the small pool gets heated regularly.
The bottom line
A small pool under 5,000-6,500 gallons doesn’t need — and often can’t easily accommodate — the 240V heat pumps sized for this site’s other guides. The FibroPool FH120 is the established-brand pick if avoiding an electrician is worth paying a premium for, the AQUASTRONG 16,000-18,000 BTU heat pump is the budget alternative in the same 120V category, and a stack of Intex Solar Mats is the cheapest supplement if a few extra degrees on sunny days is all that’s needed. If your pool is closer to 10,000 gallons, see our best pool heater for a 10,000-gallon pool picks instead — that’s where a standard 240V heat pump starts to make financial sense. For the full type-by-type breakdown across every pool size, see our best pool heater pillar guide.