Comparing Blower Quotations Like for Like: Basis, Efficiency and Hidden Exclusions

By the NextAir Systems engineering team. Last reviewed October 2026.

You asked three suppliers for a blower and received three quotations that look comparable. Prices differ by a few percent, efficiencies differ by a couple of points, and each is accompanied by a confident cover letter. Before you rank them, it is worth an hour to put them on the same basis, because the differences that matter are rarely the ones on the front page.

We work an example in which the lower headline efficiency belongs to the worse machine, and then list the exclusions that turn up most often.

The short version

• Quotation A states 4,000 Pa total pressure at 82% total efficiency. Quotation B states 4,000 Pa static at 84% static efficiency. A looks close to B, but on a common basis B’s total efficiency is about 88%, and it needs 1.6 kW less shaft power.
• At 8,000 hours and USD 0.08 per kWh the difference is about USD 1,081 a year, enough to pay back a price premium of USD 8,000 in about 7 years.
• The three usual sources of confusion are the airflow basis, the pressure basis and what is excluded from the price.
• Ask every supplier to fill in the same table, and put the test basis in writing: AMCA 210 or ISO 5801 performance is what makes a guarantee enforceable.^[1]

Step 1: one airflow basis

Convert every airflow to actual m³/h at the stated gas condition, or to normal Nm³/h, and do it for all quotes. A quotation in Nm³/h for a hot gas is a bigger fan than the same number in actual m³/h, as explained in reading a blower datasheet.

Step 2: one pressure and efficiency basis

Take two quotations for 50,000 m³/h. Quotation A gives a total pressure of 4,000 Pa and a total efficiency of 82%. Quotation B gives a static pressure of 4,000 Pa and a static efficiency of 84%. Assume the outlet velocity is 18 m/s, which gives a velocity pressure of 194 Pa.

Item	Quotation A	Quotation B
Stated pressure	4,000 Pa (total)	4,000 Pa (static)
Stated efficiency	82% (total)	84% (static)
Shaft power at the stated duty (kW)	67.8	66.1
Equivalent total pressure (Pa)	4,000	4,194
Equivalent total efficiency	82%	88.1%

Worked example. The shaft power follows from airflow × pressure ÷ efficiency. For A: 13.89 m³/s × 4,000 Pa ÷ 0.82 = 67.8 kW. For B: 13.89 × 4,000 ÷ 0.84 = 66.1 kW. B uses 1.6 kW less. Converted to a common total basis, B’s total pressure is 4,194 Pa and its total efficiency is 88.1%, which is 6.1 points better than A, not two. The headline numbers understated B’s advantage because they were on different bases.

Reverse the case and the same effect hides a weaker machine. The only protection is to put every quote on one basis before ranking. At USD 0.08 per kWh and 8,000 hours, A’s extra 1.6 kW costs about USD 1,081 a year including motor losses. Over 15 years at an 8% discount rate the present value is about USD 9,253, more than a USD 8,000 price premium would justify, as the model in the life-cycle cost article shows.

Notice what this means for negotiation. A supplier whose sheet shows a lower headline number is not necessarily offering a worse machine, and one with a higher number is not necessarily offering a better one. The only fair question is what each machine will draw at your duty point, which you can compute in two minutes once the bases agree.

Step 3: the operating point, not the peak

A supplier can quote the peak efficiency of the fan family, which is higher than what you will get at your duty point. Ask each supplier to mark the duty point on the performance curve and quote the efficiency there. Check that it is close to the best-efficiency point and well away from the stall region, as explained in the operating point guide.

Step 4: the exclusions

• Motor and drive. Is the motor included, and what efficiency class? Is a VFD or soft starter included?
• Bearings and couplings, guards, base frame and anti-vibration mounts.
• Inlet and outlet items, such as inlet cones, flexible connections, silencers, dampers and inlet vanes.
• Insulation and painting or coating, especially for hot or corrosive service.
• Instrumentation, vibration probes, temperature sensors and monitoring.
• Testing. Witnessed performance testing, balancing grade and any mechanical run test.
• Spares and commissioning, and the warranty terms, including what voids them.
• Delivery basis. Ex-works, delivered or installed, which changes the comparison completely.

Step 5: the guarantee

A performance guarantee is only worth something if it names the test: the standard, the tolerance, and who pays if it fails. The usual standards are ISO 5801 and AMCA 210, covered in our testing guide. AMCA’s Publication 201 also notes that installed performance can fall below the laboratory rating because of the system, and that fans of the same type from different manufacturers do not necessarily react the same way,^[1] so the guarantee should say where it applies.

A template to send to every bidder

1. Airflow at the gas condition (actual and normal).
2. Total pressure and static pressure at the duty point, and the gas density used.
3. Total and static efficiency at the duty point, and the peak efficiency.
4. Shaft power, motor rating, motor efficiency class and drive type.
5. Speed, wheel diameter and tip speed.
6. Sound power level.
7. Scope inclusions and exclusions, line by line.
8. Test standard, tolerance and guarantee terms.

Where this fits with NextAir

NextAir will complete a table like this for any enquiry and is happy to see competing quotations normalised alongside ours. Send your specification to our centrifugal blower manufacturer team. Our centrifugal blower guide explains the range, and the chemical and fertiliser page covers corrosive duties where the exclusions matter most.

Sources

1. AMCA / ANSI Webstore. AMCA 201-23 Fans and Systems.
2. Plant Engineering (US DOE Motor System BestPractices material). Building energy efficiency into fan systems.

Figures and tables on this page are calculated or compiled by NextAir Systems and you are welcome to reuse them with a link back to this article.

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