RV Water Pump Calculator: What Size Water Pump Do I Need?

The right RV water pump is the smallest one that still holds pressure with everything you run at once open — and the number on the box cannot tell you which that is. A pump’s rated GPM is its flow at 0 psi. On SHURflo’s own data sheet its 3.0 GPM pump makes 1.5 at 30 psi, and a shower plus a kitchen faucet pull it down to about 13 psi.

What size water pump do I need for my RV?

Start with what is open at the same time, not with the size of the rig. On the calculator’s defaults — a 2.5 gal/min shower and a 2.2 gal/min kitchen faucet running together, and 25 psi wanted at the pump — the answer is SHURflo’s 4.0 GPM 4048, which settles at 28.8 psi and delivers 3.0 gal/min, about 1.5 to each fixture.

Change one input and the answer moves:

What is open	Pressure wanted	Smallest pump that holds it	Holds
Shower alone	25 psi	SHURflo 4008 (3.0 GPM)	29.4 psi
Shower and kitchen faucet	20 psi	Remco Aquajet ES (3.4 GPM)	21.8 psi
Shower and kitchen faucet	25 psi	SHURflo 4048 (4.0 GPM)	28.8 psi
Shower and kitchen faucet	30 psi	Remco Aquajet RV (5.3 GPM)	31.3 psi
Shower, kitchen and bathroom faucets	25 psi	Nothing in our records	21.2 psi at best

Federal-maximum fixtures: 2.5 gal/min at 80 psi for a shower head, 2.2 at 60 for a faucet. Pressures at the pump, from each maker’s published curve.

The guides that rank for this question answer it by rig size instead, and they do not agree. A small RV needs 2.0 to 2.5 GPM on LATCH.IT’s guide, “around 3.5” on Camper Rules’, and anything from 1.0 to 2.8 on Prked’s. None of them does the sum above, and two of the four — LATCH.IT and Kohree — recommend the pumps they sell.

What does 3.0 GPM on an RV water pump actually mean?

It is the flow with nothing to push against — 0 psi, a hose running into a bucket. Both makers here publish the rest of the curve, and none of the four ranking guides quotes it:

Pump	On the box	At 20 psi	At 30 psi	At 40 psi	At 50 psi
SHURflo Revolution 4028	2.3	1.43	1.22	1.00	0.24
SHURflo Revolution 4008	3.0	1.8	1.5	1.2	0.5
Remco Aquajet ES	3.4	2.7	2.3	2.0	1.6
SHURflo 4048 High Flow	4.0	3.2	3.0	2.0	0.95
Remco Aquajet RV	5.3	4.0	3.25	2.5	2.25

Gal/min, from each maker’s data sheet. SHURflo’s are “typical performance at 12V”; Remco’s spec sheets do not state a voltage.

Three things fall out of that table that no rating on a box would tell you:

• The 3.0 GPM pump makes half its label at 30 psi — 1.5 gal/min, on SHURflo’s own sheet.
• The label order breaks by 40 psi. Remco’s 3.4 GPM Aquajet ES makes the same 2.0 gal/min there as SHURflo’s 4.0 GPM 4048, and at 50 psi it makes 1.6 against 0.95.
• A 1.3 GPM gap on the box is 0.25 at 30 psi. That is the 5.3 GPM Aquajet RV against the 4.0 GPM 4048.

Why the pressure drops when two taps are open

A fixture is a fixed opening, and water through a fixed opening rises and falls with the square root of the pressure across it — the liquid flow relation in Swagelok’s valve sizing bulletin, adapted from the ISA standard for sizing valves. That is why the federal flow limits name a pressure: a shower head is 2.5 gal/min “at a flowing pressure of 80 pounds per square inch”, a faucet 2.2 at 60 (10 CFR 430.32).

Put the two curves together and the pump settles where they cross. On the SHURflo 4008:

• Shower alone. At 20 psi the pump makes 1.8 gal/min and the shower would take 1.25; at 30 psi, 1.5 against 1.53. They meet at 29.4 psi, about 1.5 gal/min.
• Shower and kitchen faucet. The pair would take 1.78 gal/min at 10 psi, where the pump makes 2.2, and 2.52 at 20, where it makes 1.8. They meet at 13.4 psi, and each fixture gets about 1.0 gal/min.

That is the shower going weak when someone rinses a plate: not a failing pump, but the pump doing exactly what its data sheet says. Lower flow at the head is not all bad news — on a tank water heater it means more minutes of hot water, which our hot water calculator works out.

Is a bigger RV water pump worth it?

Sometimes — but the upgrade is electrical as much as it is plumbing, and the makers say so in their own manuals.

	SHURflo 4008	SHURflo 4048	Remco Aquajet ES	Remco Aquajet RV
Amps at 30 psi	5.1	7.3	6.5	10.0
Fuse	10 A	15 A	7.5 A in the box; 10 A in the manual	10 A in the box; 15 A in the manual
Wire	16 AWG minimum, 12 recommended	14 AWG minimum, 12 recommended	Existing wiring in most RVs, per Remco	14 AWG to 10 ft, 12 to 20 ft, 10 beyond

From SHURflo’s data sheets and 911-1008 and 911-1024 manuals, and Remco’s spec sheets and 2025 Aquajet manual.

SHURflo’s 4008 to its 4048 more than doubles the pressure on the default two-fixture case, 13.4 psi to 28.8, and doubles the current, 3.6 A to 7.2. It also wants 14 AWG wire where the 4008 accepts 16, and a 15 A fuse where the 4008 takes 10. Both SHURflo manuals add that an Intellitec pump controller rated 7.5 A must be replaced or given a relay.

Remco’s Aquajet RV is at its full 10 A from 30 psi up on Remco’s own sheet, and the 2025 manual warns it “may draw more current (Amps) than the pump(s) they replace”. If the old circuit drops more than a volt with the existing pump running, Remco says to “pull a new heavier (10-12AWG) ‘hot’ wire to the pump AND use a 30 amp relay”. On the default it buys 2.5 psi over the 4048 for about 2.8 A more. Remco’s Aquajet ES is the easy one: its manual says it “should be compatible with the existing electrical wiring for most RVs”.

Our 12V wire size calculator sizes the run for a new pump’s current. At 12 V, the 4008’s 5.1 A at 30 psi is about 61 W and the 4048’s 7.3 A about 88 W — the two ends of the water pump row in our lithium battery sizing guide.

Do I need an accumulator tank?

Not with a by-pass pump, according to the people who make them. Both SHURflo manuals say “No need for an accumulator with by-pass pumps”, and Seaflo’s 42 series sheet says “No need for an accumulator tank, and no more pump cycling.” Prked’s guide, for anyone who sticks with a standard pump, calls the accumulator “The Secret Weapon” under a heading that reads “Why You Need an Accumulator Tank”.

SHURflo still sells two — a 24 oz nylon tank and a 2 gallon stainless one — and if you fit one, its catalog says it “should be charged to the restart [On] pressure of the pump”: 40 psi on the 4008 and 4048. Remco’s answer to a pump that “rapidly cycles on/off with water demand” is its own pulsation dampener, along with checking any inline filter.

If a by-pass pump does cycle, SHURflo’s manual points at the plumbing first: “restrictive plumbing and flow restrictions in faucets/shower heads”, a water filter that is not “on separate feed line”, or a shut-off pressure set too low.

When the maker publishes no curve

Two pumps that turn up in the ranking guides are missing from the calculator, because their makers do not publish the numbers it needs.

• Seaflo 42 series. The spec sheet gives “full 3.0 GPM open demand”, 7.5 A, and a switch adjustable from 45 to 65 psi, set at 55. Nothing between 0 psi and shut-off.
• Lippert Flow Max. Lippert’s product page describes it as “averaging 50 PSI” with “an average of over 3.0 gallons per minute”. None of the five curves above makes even 2.5 gal/min at 50 psi. The same page lists “9.5 max amp (15 amp required)”; Lippert’s own manual says “A 10 amp fuse is required”.

The five pumps compared

Model	On the box	At 30 psi	Shut-off	Max draw	Fuse	Buy
SHURflo Revolution 4028	2.3 GPM open flow, at 0 psi	1.22 GPM	50 psi, restarting at 40 psi	5 A in Pentair's catalog; the data sheet's own table reaches 5.3 A at 55 psi	7.5 A recommended	Check price(opens in a new tab)
SHURflo Revolution 4008	3.0 GPM open flow, at 0 psi	1.5 GPM	55 psi, restarting at 40 psi	7.5 A	10 A recommended	Check price(opens in a new tab)
Remco Aquajet ES	3.4 GPM maximum flow, at 0 psi	2.3 GPM	65 psi	6.5 A	7.5 A included, per the spec sheet; the 2025 manual says to use only a 10 A	Check price(opens in a new tab)
SHURflo 4048 High Flow	4.0 GPM open flow, at 0 psi	3.0 GPM on the 2016 data sheet; 2.8 in the 2014 manual	55 psi, restarting at 40 psi	10 A in Pentair's catalog; the data sheet's own table reaches 10.4 A at 65 psi	15 A recommended	Check price(opens in a new tab)
Remco Aquajet RV	5.3 GPM maximum flow, at 0 psi — the 2025 manual's cover still says 5.0	3.25 GPM	65 psi	10 A	10 A included, per the spec sheet; the 2025 manual says to use only a 15 A	Check price(opens in a new tab)

Where this goes wrong

1. Buying by the number on the box. It is the flow at 0 psi. Compare pumps at 30 or 40 psi, where your fixtures actually run.
2. Sizing for every fixture at once when you take turns. A shower alone holds about 29 psi on a stock 3.0 GPM SHURflo.
3. Upgrading the pump and not the wire. A 4048 wants 14 AWG and a 15 A fuse; a 16 AWG circuit is below SHURflo’s minimum for it.
4. Expecting 40 to 70 psi on the pump. Camper Rules says a camper “should have a PSI level of about 40 - 70”. SHURflo’s pumps shut off at 55 and restart at 40, and with one shower open the 4008 Camper Rules recommends sits near 29.
5. Adding an accumulator to fix a by-pass pump. SHURflo says it does not need one. Look for a restriction first.

Questions worth answering