How many class room hours does the typical university teacher teach per week?
There is no “typical” number in this matter. Let's take a few examples:
UK, lecturer: it's usually a full-time position, so you have to put in 35-40 hours per week. The ratio of lecture time over all the rest (preparation, departmental committees, etc.) depends on the contract, but I have rarely seen it pushed past 1:1 (which means roughly 20 hours of teaching, maybe 25 at most).
France, "PRAG": this is the position of a high-School teacher detached to a university, and the closest one to a lecturer position. Their nominal teaching load is 384 hours per year, with a weight of 1.5 for lectures and 1 for exercises sessions. But for one the year is very short, from about 23 to 26 weeks, so that means about 15 hours per week, and this is only the nominal amount. In any cases, they (voluntarily or not) have to teach additional hours, which are paid in addition (to a lower rate than nominal hours).
As a point of comparison: a French high-school teacher would have 18 teaching hours per week.
Other comparison points, less relevant to the question as they are for teaching+research positions:
France, associate professor (maître de conférences): junior-level position, supposed to be half teaching and half research. This has a fixed number of 192 teaching hours per year. If you consider that those are spread on 30 weeks, it gives 6.4 hours per week. Even considering it is not a teaching-only position, that number is lower than the one you quote.
France, full professor (professeur des universités): same number of hours in theory, but as you gain seniority you can do more full-class teaching (with bigger groups), of which every hour counts as 1.5 hour in your yearly total. Through this, and other mechanisms, senior professors usually have fewer hours to teach.
20 hours per week for most teaching only positions is normal. I have seen Profs with major research responsibilities that at times have had 20 hours of teaching as well.
My rule of thumb for a course: You will spend 2 to 3 times the amount of teaching you do preparing the first time you teach a course and this decreases as years go on for that same course (a new course requires considerable amount of time for preparation again).
First time I was teaching advanced thermodynamics and fluid mechanics courses I was spending two full days per 2 hours of teaching actually! but then after three years it was down to preparing 2 hours for 2 hours of teaching.
Your numbers seem right to me. In short 20 hours of teaching = virtually no time to do research.
I assume you are talking about in term time teaching per week and not total teaching per year/52. I have never heard of a permanent full time position having a heavier teaching load than a 5-5. Some people then choose to teach summer courses (but this wouldn't effect you teaching hours per term week). Often this type of load includes some repetition so you might only have to prep 7 courses of which only 1 might be a new prep. The amount of classroom contact time for each course might be as low as 3 hours but could climb to 6. There might also be some office hour contact (which you might count as teaching contact). Many full time teaching jobs have lighter loads and can be as low as 3-3. Research intensive departments can have typical teaching loads as low as 1-1. Adjuncts often teach as high as 6-6 in order to make ends meet.
There is so much more than just the number of taught hours that influence teaching load. I think you need to look at number of classroom hours, number of unique preps, office hours, and marking.