I'm the person who approves—or rejects—every heating unit before it reaches a customer. At our facility, that means I review roughly 200 unique items annually. And I ‘ve learned that the most dangerous thing you can do when ordering a replacement heater is to assume it’ll just work. I learned that the hard way.

In Q1 of last year, we received a batch of fifteen ceramic fan heaters for a commercial retrofit. The spec sheet looked perfect. The price was competitive. Then I actually put one on the test bench. The internal thermal cutoff was rated for 85°C—our contract required 110°C. Normal tolerance for this part is ±5°C. The vendor claimed it was “within industry standard.” We rejected the entire batch, delayed the project by two weeks, and incurred a $3,800 rush-shipping fee to get compliant units. I still kick myself for not catching it in the pre-order spec review.

So, here is the exact checklist I now use before approving any heating component order. It’s not a theory. It’s a scar.

Who Is This For?

This checklist is for anyone responsible for purchasing or specifying a heating unit—whether it’s a Dimplex night storage heater for a residential flat, a ceramic heater for a workshop, or a hot water heater replacement for a commercial building. If you’re the person whose name is on the purchase order, use this.

There are seven steps. Do them in order.

Step 1: Verify the Spec Sheet Against Your Actual Conditions

Sound obvious? It’s not. The spec sheet describes ideal conditions. Your installation site is rarely ideal.

Check these three numbers specifically:

  • Thermal cutoff rating. Ask: what happens if the airflow is partially blocked? If the cutoff trips too early, the unit cycles constantly. If it trips too late, you have a fire risk.
  • Input voltage tolerance. A unit rated for 240V will behave differently on a line that’s actually delivering 228V. I’ve seen fan motors fail prematurely because the voltage sag was outside the spec.
  • Ingress Protection (IP) rating. If the unit is going in a garage or workshop, it needs at least IP54 to handle dust and occasional moisture. An IP20 unit won’t last a season.

Checkpoint: If the spec sheet doesn’t list these three values, call the manufacturer before you order. If they can’t provide them, find a different product.

Step 2: Confirm the Mounting Kit is Included (It’s Never Obvious)

Here’s a mistake I’ve made twice: ordering a replacement hot water heater element and assuming the gasket and locknut were in the box. They were not. That meant an extra trip to the supplier, a $12 part, and an hour of lost labor.

The same applies to wall-mounted heaters. Does the bracket come with the Dimplex night storage heater, or is it a separate SKU? Read the “what’s in the box” section of the listing. If it’s vague, email the vendor. Get it in writing.

Step 3: Check the Airflow Direction (This is the One Everyone Forgets)

This step is so common I’d call it the professional’s secret. I cannot tell you how many installations I’ve seen where the unit was functional but the airflow was fighting itself.

For any unit with a fan—ceramic heaters, forced-air unit heaters, or blowers like an EGO blower—verify the inlet and outlet orientation. Some units are designed for horizontal airflow, others for vertical. I’ve had to reject 18 units in one order because the air inlet grille was facing a wall, and the spec sheet didn’t specify required clearance. The vendor’s defense? “We can’t predict installation choices.” Fair, but if we’d checked the clearance requirement before ordering, we would have picked the model with the side-mounted intake.

Checkpoint: Look at the installation manual for minimum clearance from walls, ceilings, and obstructions. It’s usually on page 2 or 3. If it’s not there, ask.

Step 4: Ask “What Is NOT Included?”

This is where transparency separates trustworthy vendors from the rest. I make it a standard practice: after I get a quote, I send back a one-line email. “Can you list everything not included in this price?”

You’d be surprised what comes back. Things I’ve seen excluded:

  • Thermostat (for a unit that requires external control)
  • Wall-mounting bracket
  • Power cord (carbon dioxide washing machine? No, but I’ve seen heater units without a cord)
  • Warranty registration (you have to pay extra)

The vendor who lists all fees upfront—even if the total looks higher—usually costs you less in the end. The one who gives you a low base price and adds “installation accessories” is the one who’ll bill you $200 for a $12 bracket.

Step 5: Check the Air Filter Direction (Really)

Which way does air filter go? This is the most common question we get from installers. And I understand why: on some units, the filter frame isn’t labeled clearly.

For a heater unit, the filter direction matters because the airflow pulls through the filter. If you install it backward, the filter’s structural mesh is on the wrong side, and it can collapse under airflow, restricting heat exchange and causing the unit to overheat.

When we specify our units, we now require that the filter frame has an arrow stamped on both sides—not just on the frame edge, where it can be hidden. If your unit has a filter, check for that arrow. If it’s not there, use a permanent marker to draw one after the first correct installation.

Quick rule: The arrow always points toward the blower/motor. Away from the intake. If you can’t find the arrow, assume the filter goes with the dirtier side facing outward (intake side).

Step 6: Price-Check by Total Installed Cost, Not Unit Price

I once approved a purchase of 30 Dimplex ceramic heaters because the per-unit price was 18% lower than the competitor. Total installed cost came out 12% higher, because we had to buy separate thermostats, longer brackets, and a special wiring adapter.

According to USPS pricing as of February 2025, your postage costs can vary by up to 40% based on envelope size and weight. But when you’re buying heaters, the variation isn’t in stamps—it’s in what you need to add to make the unit work in your building.

Always calculate the installed cost: unit price + all required accessories + labor for extra steps + any known service costs in year one. That’s your real number.

Step 7: Get One Reference Installation (and Call Them)

This is the step I started doing after 2022. Before approving a new model, I ask the vendor for a reference who has installed that exact unit in a similar application. If they can’t provide one, I’m nervous.

When I called a reference for a Dimplex storage heater model we were evaluating, I learned that the door latch on the previous version had a defect—it opened during shipping. The vendor had fixed it in the current production run, but I wouldn’t have known to check unless the reference told me. Saved us having to inspect every unit upon delivery.

Common Mistakes I Still See

Here are the issues I catch most, in order of frequency:

  1. Wrong thermal cutoff. I’ve said it before, but it’s true. This is the number one reason I reject a batch.
  2. Missing mounting hardware. Not a safety issue, but it delays installation and creates cost.
  3. Filter direction wrong. It’s a simple fix, but it causes overheating if ignored.
  4. Voltage mismatch. Ordering a 240V unit for a building wired at 208V. It happens more than you think.
  5. Assuming the spec sheet is the whole story. It isn’t. Verify the conditions at your site.

You don’t have to be perfect. I’m not. But if you run this checklist before you hit “buy,” you’ll catch the things that cost time, money, and reputation.