42,000 BTU (3.5-ton) Heat Pumps: Which One to Buy
A 42,000 BTU heat pump is a 3.5-ton system, an in-between size for about 1,400 to 1,750 sq ft by the common rule of one ton per 400 to 500 sq ft. For a home with ducts, buy the Goodman GLZS4BA4210 + AMST42CU1300 ($4,333 on Amazon) and have a licensed installer fit it. Goodman's warranty depends on that.
Our pick at 3.5 tons
Goodman GLZS4BA4210 + AMST42CU1300
$4,333 on Amazon
Check price on Amazon- Outdoor unit + air handler: the pairing its certified rating is for.
- Rated 15.2 SEER2 and 7.8 HSPF2 (AHRI), above the federal floor for heat pumps in every region (14.3 SEER2, 7.5 HSPF2).
- On a 5°F day it still makes 20,000 BTU of heat, 51% of its rating at 47°F. Plan backup heat for colder days.
- Amazon's listing says 14.3 SEER2; AHRI certifies 15.2 with this air handler.
Need something different?
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$2,819.95 on AmazonKeeping your indoor unit
Goodman GLZS4BA4210
Outdoor unit only, $1,513.05 less. Your installer confirms your indoor unit matches it.
Why 3.5 tons is harder to shop for
3.5 tons is an in-between size. Far fewer systems are certified at 3.5 tons than at 3 or 4 tons, so an installer may quote one of those instead. That is fine when your load calculation lands close to it; ask to see the numbers.
One size down, the 3-ton Goodman system (Goodman GLZS4BA3610 + AMST36CU1300) costs $4,310.14, $22.86 less, for about 1,200 to 1,500 sq ft, and makes 17,400 BTU of heat at 5°F. One size up, the 4-ton system (Goodman GLZS4BA4810 + AMST48CU1300) costs $4,910.07, for about 1,600 to 2,000 sq ft, and makes 20,000 BTU at 5°F. Pick the size the load calculation gives, not the price.
Replacing a unit? The size is in the old outdoor unit's model number: 42 means 3.5 tons.
Will it keep up in winter?
On a 5°F day this Goodman makes 20,000 BTU of heat. The middle ducted 3.5-ton heat pump certified makes 21,600, so it is close to typical. Plan backup heat for the coldest nights all the same.
What it costs
| How you buy it | Typical price |
|---|---|
| Outdoor unit only, on Amazon | from $2,819.95 |
| Outdoor unit + air handler, on Amazon | from $4,333 |
| Ducted heat pump, 3.5-ton, installed by a contractor | $10,000 to $18,000 |
Amazon prices read today. Installed prices are U.S. typical for a replacement on existing ducts, equipment, labor and permit together (published 2026 data, compiled July 2026).
Questions buyers ask
- How much does a 3.5-ton heat pump cost?
- $2,819.95 to $4,333 on Amazon for the Goodman listings here, and typically $10,000 to $18,000 installed by a contractor.
- Should I get 3 tons or 3.5 tons?
- Go by the load calculation. By the rule of thumb, 3 tons suits about 1,200 to 1,500 sq ft and 3.5 tons about 1,400 to 1,750. On Amazon today the 3-ton Goodman system is $22.86 less than the 3.5-ton.
- Is a 3.5-ton heat pump hard to find?
- There is less choice: far fewer systems are certified at 3.5 tons than at 3 or 4 tons. Goodman makes one, sold here as the Goodman GLZS4BA4210 + AMST42CU1300.
- Which air handler goes with a 3.5-ton heat pump?
- The one its AHRI rating names. For this pick that is the AMST42CU1300, which ships in the same listing.
- Can I buy a heat pump online and install it myself?
- You can buy it online, but a licensed installer has to fit it: charging the refrigerant needs EPA Section 608 certification. Goodman says it gives no warranty on equipment a homeowner buys online unless the unit is installed by a dealer who follows all federal, state and local codes and licensing rules.
Every certified 3.5-ton heat pump (239)
The systems below are certified at about 42,000 BTU, ducted and ductless, most sold through contractors. If an installer quotes one, find it here to check its efficiency and how much heat it keeps on a 5°F day. The table shows the 20 with the highest HSPF2; the full product list has all 239.
The 20 highest-HSPF2 of 239 certified units
| Brand & model | HSPF2 | Capacity | Heat at 5°F | $/MMBtu | Buy | |
|---|---|---|---|---|---|---|
| TOSHIBA CARRIER RAV-BP421AT2P-UL | 11.2 | 3.5 ton | 33,400 BTU | $16.81 | installer | |
| Mitsubishi Electric MXZ-SM42NLHZ | 11.1 | 3.5 ton | 48,000 BTU | $16.96 | installer | |
| Mitsubishi Electric PUMY-HL42NKMU | 11.1 | 3.5 ton | 48,000 BTU | $16.96 | installer | |
| MDV MOE30U-48HFN1-M[X] | 11.0 | 3.5 ton | 56,500 BTU | $17.12 | installer | |
| LG KUMXA421A | 11.0 | 3.5 ton | 44,000 BTU | $17.12 | installer | |
| LG LMU421HHV | 11.0 | 3.5 ton | 44,000 BTU | $17.12 | installer | |
| LG KUSXA421A | 10.8 | 3.5 ton | 43,500 BTU | $17.44 | installer | |
| LG KUSXB421A | 10.8 | 3.5 ton | 40,000 BTU | $17.44 | installer | |
| Hitachi PAS-48BUFASDQ1 | 10.8 | 3.5 ton | 36,600 BTU | $17.44 | installer | |
| LG LUU420HHV | 10.8 | 3.5 ton | 40,000 BTU | $17.52 | installer | |
| Fujitsu AOUH42KUAH1 | 10.6 | 3.5 ton | 48,000 BTU | $17.76 | installer | |
| Mitsubishi Electric MXZ-SM42NAMHZ2 | 10.6 | 3.5 ton | 44,000 BTU | $17.85 | installer | |
| Mitsubishi Electric PUMY-HP42NKMU2 | 10.6 | 3.5 ton | 44,000 BTU | $17.85 | installer | |
| Trane / Mitsubishi Electric NTXMSH42A152B | 10.6 | 3.5 ton | 44,000 BTU | $17.85 | installer | |
| 1HVAC EZ-48Z-M5B | 10.5 | 3.5 ton | 37,000 BTU | $17.93 | installer | |
| ACIQ ACIQ-42Z-E-HH-M5 | 10.5 | 3.5 ton | 34,000 BTU | $17.93 | installer | |
| AUX AM5-H42/2DR3B | 10.5 | 3.5 ton | 34,000 BTU | $17.93 | installer | |
| AUX ASUM42HPMULO | 10.5 | 3.5 ton | 34,000 BTU | $17.93 | installer | |
| Armbridge AB-GTMH42-230VO | 10.5 | 3.5 ton | 34,000 BTU | $17.93 | installer | |
| Armbridge AB-GTMR42-230VO | 10.5 | 3.5 ton | 34,000 BTU | $17.93 | installer |
Capacity and efficiency are AHRI-certified values; $/MMBtu is computed by us from EIA energy prices — see methodology. Heat at 5°F is the number that decides whether a heat pump keeps up in real cold, and most listings omit it.