Ventilation FansBathroom & Utility
Delta SLM70D Ventilation Fan Manual
Setup, everyday use, maintenance and troubleshooting for the 70 CFM bathroom exhaust fan, with verified specifications.
- Airflow70 CFM
- Sound0.8–2 sones
- Efficacy7 CFM/W
- Duct size3 in. round
About the Delta SLM70D
This guide covers the Delta SLM70D, a 70 CFM bathroom exhaust fan on the ENERGY STAR certified list. It belongs to the BreezSlim line.
It has rated airflow settings of 40 and 70 CFM (2-speed). At 0.25 in. of static pressure — closer to a real duct run with elbows and a roof cap — airflow is 56.1 CFM. Its sound rating is 0.8–2 sones, which is quiet to moderate — audible, but easy to talk over. It connects to a 3 in. round duct.
Fan efficacy is 7 CFM per watt, which means the motor draws roughly 10 W at 70 CFM. That efficacy is higher than 59% of the 822 Bathroom & Utility models in our database.
Specifications
| Brand | Delta |
|---|---|
| Model number | SLM70D |
| Model name / series | BreezSlim |
| Fan type | Bathroom & Utility |
| Rated airflow | 70 CFM |
| Fan efficacy | 7.0 CFM/W |
| Second airflow setting | 40 CFM |
| Efficacy at second setting | 12.7 CFM/W |
| Airflow at 0.25 in. w.g. | 56.1 CFM |
| Sound level (highest rated) | 2.0 sones |
| Sound level (lowest rated) | 0.8 sones |
| Number of speeds | 2 |
| Duct connection (round) | 3.0 in. |
| Integrated light | No |
| ENERGY STAR Most Efficient | No |
Safety information
- Turn off power at the circuit breaker before installing, wiring or cleaning the fan, and confirm it is off with a non-contact voltage tester.
- Install and wire the fan in accordance with the instructions and local electrical and building codes. If you are unsure, hire a licensed electrician or HVAC contractor.
- Always duct the fan to the outdoors. Never terminate exhaust in an attic, crawl space, soffit vent or wall cavity — trapped moisture and grease cause mold, rot and fire risk.
- If the fan is installed over a bathtub or shower, it must be listed for that location and is typically required to be on a GFCI-protected circuit — check the installation instructions.
- Do not use the fan to exhaust explosive or flammable vapors.
Installation and first-time setup
- Check the fan size
For a bathroom up to 100 sq. ft. with an 8 ft ceiling, plan on about 1 CFM per square foot, and at least 50 CFM. At 70 CFM this fan suits a bathroom up to roughly 70 sq. ft. by that rule.
- Choose the location
Mount the fan in the ceiling between the shower and toilet, or as close to the shower as the listing allows, and away from the door so it draws air across the room.
- Plan the duct run
Use 3 in. round smooth metal or insulated flexible duct no smaller than the fan's collar. Keep the run as short and straight as possible, pull flexible duct taut, and slope horizontal runs slightly toward the exterior so condensation drains out.
- Insulate and terminate
In an unheated attic, use insulated duct to prevent condensation. End the run at a roof or wall cap with a backdraft damper — never in the attic or a soffit vent.
- Mount and wire
Fasten the housing to the joists with the supplied brackets, seal the gap between housing and ceiling to stop air leakage, and make the electrical connections inside the wiring box. Attach the grille.
- Test
Restore power and hold a single sheet of tissue near the grille — it should be drawn firmly against it. Check outdoors that the damper opens when the fan runs.
Using your ventilation fan
How long to run the fan
Turn the fan on when you start a bath or shower and leave it running for about 20 minutes afterward to clear moisture from the room and surfaces. A timer switch or humidity-sensing control makes this automatic and prevents the fan from running all day.
Using multiple speeds
With settings from 40 to 70 CFM, the lower setting can run continuously for background ventilation while the higher setting clears steam after showers. Continuous low-speed operation is how many homes meet whole-house ventilation requirements.
Care and maintenance
| When | What to do |
|---|---|
| Every 3–6 months | Remove the grille (it usually unclips with spring wires), wash it in warm, soapy water and vacuum dust from the housing and fan blades with power off. |
| Every year | Check outdoors that the damper flap opens freely and the exterior cap is clear of lint, nests and debris. |
| Every few years | Inspect accessible duct runs for disconnected joints, crushed sections or condensation. |
Troubleshooting
Weak airflow and excess noise are almost always caused by the duct system rather than the fan. Turn off power at the breaker before removing the grille or touching the motor.
| Problem | Possible cause | What to try |
|---|---|---|
| Fan runs but moves little air | Damper stuck closed; duct crushed, disconnected or too long; dirty grille or filter. | Check the exterior damper and cap, inspect the duct, and clean the grille or filters. |
| Louder than expected | Restrictive or undersized duct; loose grille; housing not secured. | Use duct at least as large as the collar (3 in. round), tighten the grille and mounting screws. |
| Rattling or flapping sound | Backdraft damper fluttering in wind; loose duct. | Secure the duct and check that the damper closes fully; a wall cap with a better damper may help. |
| Water dripping from the grille | Condensation in an uninsulated duct; duct sloped back toward the fan. | Insulate the duct in unheated spaces and slope it toward the exterior. |
| Fan will not start | Breaker off; switch or timer failed; motor plug loose in the housing. | Check the breaker, test the switch, and with power off confirm the motor is plugged into its receptacle. |
| Cold drafts from the fan when off | Damper not closing; unsealed housing. | Free or replace the damper and seal around the housing. |
Energy use and running costs
Ventilation fan certification lists airflow and efficacy rather than annual energy use. From 70 CFM at 7 CFM/W, the Delta SLM70D draws roughly 10 W. The table estimates yearly use at an average electricity price of $0.17 per kWh.
| Scenario | Power | Energy per year | Cost per year |
|---|---|---|---|
| After showers, 1 h/day | 10 W | 3.7 kWh | $0.62 |
| Continuous at 40 CFM, 24 h/day | 3 W | 28 kWh | $4.69 |
The motor is only part of the cost: every cubic foot exhausted is replaced by outdoor air that must be heated or cooled. Run the fan as long as needed to clear moisture, then let a timer or humidity control switch it off — unless it is providing intended continuous ventilation.
Frequently asked questions
How many CFM is the Delta SLM70D?
It is rated at 70 CFM, with airflow settings of 40 and 70 CFM, and delivers 56.1 CFM at 0.25 in. of static pressure.
How loud is the Delta SLM70D?
It is rated at 0.8–2 sones, which is quiet to moderate — audible, but easy to talk over. Restrictive ductwork can make any fan louder than its rating.
What size duct does the Delta SLM70D need?
It has a 3 in. round duct connection. Use duct at least that size all the way to the exterior cap; reducing it cuts airflow and raises noise.
What size bathroom can the Delta SLM70D ventilate?
Using the common rule of 1 CFM per square foot for bathrooms up to 100 sq. ft. with 8 ft ceilings, 70 CFM covers a bathroom up to about 70 sq. ft.
How much electricity does the Delta SLM70D use?
With an efficacy of 7 CFM/W it draws roughly 10 W at 70 CFM. Running one hour a day costs about $0.62 a year at $0.17/kWh.
Does the Delta SLM70D have a light?
No. The certified configuration does not include a light.
Sources and disclaimer
Specifications on this page come from the ENERGY STAR certified ventilation fans dataset published by the U.S. Environmental Protection Agency (record certified January 18, 2018), retrieved October 7, 2026.
The setup, operating, maintenance and troubleshooting guidance is written by ManualHarbor's editors for this specific product type and configuration. It is an independent guide — not a reproduction of the manufacturer's manual — and ManualHarbor is not affiliated with Delta. Always follow the safety instructions, installation requirements and warranty terms supplied with your unit, and contact Delta or an authorized service provider for warranty repairs and replacement parts.
Running-cost figures use assumed U.S. average utility prices and are estimates for comparison only. See our editorial methodology for details.
Report a problem with this guide
Spotted a wrong value, a broken link or something unclear? Tell us and we will review it.