Intermatic WH21 electric timer

by Sam

Bought electric timer, Intermatic WH21 model, for 40-gallon AO Smith electric water heater and this is my experience so far... after one year using for water heating in residential home.

Advantages first:

My electrical bill went down by over 20%. Water heater works few hours per day only. It will be ON between 5 and 7 am and 6-8 pm and hot water temperature is around 120 F. As you can see, the timer is set in such a manner so my AO Smith water heater doesn't have to work constantly 24/7.

Very easy installation, it takes less than an hour, but you need some electrical experience.

The timer is very convenient. Intermatic WH21 model has many settings which covers almost any time you desire.


Instructions to install are poorly done but if you know what are you doing it is not hard to install. The only problem is the tight casing that makes very difficult to install #10 wire.

Comments for Intermatic WH21 electric timer

Average Rating starstarstar

Click here to add your own comments

Aug 22, 2020
Timer is fast
by: Robert Eberle

Bought a new intermatic wh 21 electric water heater timer to replace a worn out masterplumber timer which worked fine for many years. The new intermatic timer does NOT work well. It is fast 45 minutes to 1 hour and 15 minutes each day. After a 3 day trip away we returned home at 4:00 pm, The timer read 10:30 PM. One cannot know how the timer will function until it's wired which is very difficult. 10 gauge wire in a tight space. Is there an adjustment to slow it down? I have tried many resets without success. BUY ANOTHER BRAND.

Aug 02, 2018
VERY annoying...
by: Gale

The MOST annoying company... Logically you would want your water heater on in the morning and in the evening and off during the day and the night... So, for this timer you would need 4 little metal clips. Does this company include 4 little metal clips? NO, only 2 little metal clips. It probably would have cost a nickel more to have 4 clips in the box. You are supposed to BUY two more clips and the shipping costs alone are more than it's worth. COMPANY is bad...

Click here to add your own comments

Join in and write your own page! It's easy to do. How? Simply click here to return to Parts.