Cuando hace mucho calor, prefiero quedarme en casa.

In Spanish, weather is often expressed with hacer rather than a verb like to be.

So:

• Hace calor = It’s hot
• Hace frío = It’s cold
• Hace buen tiempo = The weather is nice

Literally, hace calor is something like it makes heat, but you should learn it as the normal Spanish way to talk about heat.

In this sentence, cuando hace mucho calor means when it’s very hot.

Because calor is a noun, not an adjective.

• mucho is used with nouns
• muy is used with adjectives and adverbs

So:

• mucho calor = a lot of heat / very hot
• muy caliente = very hot

Compare:

• Hace mucho calor. = It’s very hot.
• El café está muy caliente. = The coffee is very hot.

That distinction is very important in Spanish.

Because preferir is a stem-changing verb.

In the present tense, the e in the stem changes to ie in most forms:

• yo prefiero
• tú prefieres
• él/ella prefiere
• nosotros preferimos
• vosotros preferís
• ellos prefieren

So prefiero is the correct I prefer form.

This kind of change is very common in Spanish. Other verbs like this include querer → quiero and pensar → pienso.

After a verb like preferir, Spanish often uses an infinitive to say what someone prefers to do.

So:

• prefiero quedarme = I prefer to stay
• prefiero comer = I prefer to eat
• prefiero salir = I prefer to go out

Quedarme is the infinitive quedarse with the reflexive pronoun me attached to the end.

This is normal after a conjugated verb:

• Quiero irme.
• Necesito acostarme.
• Prefiero quedarme.

You could also say me prefiero quedar in some structures with other verbs, but with a single infinitive like this, attaching the pronoun to the infinitive is the standard and natural choice.

Here, quedarse means to stay or to remain.

So quedarme en casa means to stay at home.

Be careful: quedar and quedarse can have several meanings depending on context. For example:

• quedar con alguien = to meet someone / arrange to meet
• quedar bien = to look good / to turn out well
• quedarse = to stay / remain

In this sentence, the meaning is clearly to stay.

Because the verb used for to stay in this sense is normally quedarse, not just quedar.

• quedar often means things like to arrange, to be left, or to suit
• quedarse means to stay / remain

So:

• Prefiero quedarme en casa. = I prefer to stay at home.

If you said prefiero quedar en casa, that would sound wrong for this meaning.

In Spanish, en casa is a very common expression meaning at home.

• en casa = at home
• en la casa = in the house

So the sentence uses en casa because it means being at home in a general sense, not specifically inside a particular house as a physical building.

Compare:

• Estoy en casa. = I’m at home.
• Estoy en la casa de mi abuela. = I’m in my grandmother’s house.

Because this sentence is talking about a habitual or general situation:

• Cuando hace mucho calor, prefiero quedarme en casa.
• When it’s very hot, I prefer to stay at home.

Spanish uses the present tense after cuando when talking about things that happen regularly or generally.

If you are talking about a future event, Spanish often uses the present subjunctive after cuando:

• Cuando haga mucho calor, me quedaré en casa.
• When it’s very hot / when it gets very hot, I’ll stay at home.

So:

• cuando hace = general/habitual
• cuando haga = future reference

Yes, it is normal and recommended here.

The sentence begins with a subordinate clause:

• Cuando hace mucho calor, ...

In both Spanish and English, a comma is commonly used after an introductory clause like this.

So this punctuation is natural:

• Cuando hace mucho calor, prefiero quedarme en casa.

You may sometimes see commas omitted in informal writing, but the comma is the standard choice.

Yes, but the nuance is slightly different.

• prefiero quedarme en casa = I prefer to stay at home
  • This suggests remaining there instead of going out
• prefiero estar en casa = I prefer to be at home
  • This focuses more on the state of being at home

In many everyday situations, both are possible, but quedarme en casa is especially natural when the idea is not going out because of the heat.

A simple guide for Spain Spanish:

• hace ≈ AH-theh
• prefiero ≈ preh-FYEH-roh
• quedarme ≈ keh-DAR-meh

A few details:

• In most of Spain, c before e or i sounds like th in think
  • so hace sounds like AH-theh
• qu before e gives a hard k sound
  • so quedarme begins with keh-
• The stress is:
  • HA-ce
  • pre-FIE-ro
  • que-DAR-me

Because calor is usually treated as an uncountable noun in this expression, like heat in English.

So Spanish says:

• Hace mucho calor.

not normally:

• Hace muchos calores.

You are talking about a lot of heat, not many heats.

Spanish sometimes does use plural nouns in other weather expressions, but calor in this common structure is singular.

Yes. Spanish allows some flexibility.

The original sentence is:

• Cuando hace mucho calor, prefiero quedarme en casa.

You could also say:

• Prefiero quedarme en casa cuando hace mucho calor.

Both are correct. The difference is mainly one of emphasis and rhythm:

• Starting with cuando hace mucho calor highlights the condition first
• Starting with prefiero highlights your preference first

The original version sounds very natural and well-balanced.