Learn Hardcore Japanese: denkidai ga takai nara, syouenekaden ni kaeta hou ga ii. - If your electricity bill is high, you’d better switch to energy-saving appliances.

なら is a conditional particle meaning “if” or “when” based on a premise or assumption. Here it takes the known fact “電気代が高い” (“the electricity bill is high”) and says “if that’s the case, …”. Compared with other conditionals:

たら focuses on “when/after” in a more neutral or temporal sense.
と expresses automatic consequences or general truths.
Using なら highlights “given that situation” (you’ve already observed the high bill).

Why is 高い used to describe 電気代? Doesn’t 高い mean “tall”?

Many Japanese adjectives have multiple senses. 高い primarily means “high/tall,” but it also means “expensive” or “costly.” When attached to 電気代 (electricity charges), it naturally means “expensive” or “high cost.”

What does 省エネ家電 mean and how is it formed?

省エネ is an abbreviation of 省エネルギー (“energy-saving”).
家電 is short for 家電製品 (“home appliances”).
Together 省エネ家電 means “energy-saving appliances” or “energy-efficient home electronics.”

Why is the particle に used before 替えた?

With the verb 替える (“to replace” or “to switch”), the particle に marks the target you are switching to.
Example pattern:
A を B に替える = “replace A with B.”
Here:
電気代 (subject) → 高い (condition) → 省エネ家電に替えた (switch to energy-saving appliances).

Why is 替えた in the past tense instead of present/future?

In the recommendation structure ～たほうがいい, the verb before ほうがいい is always in the past (た-form). Although you’re giving advice about a future or hypothetical action, the past tense here is a fixed grammatical requirement:
Verb (past) + ほうがいい = “you’d better do ~.”

What does ～ほうがいい express?

～ほうがいい is used to give advice or make a recommendation: “You’d better ~” or “It’s better to ~.”

For positive advice: Verb (past) + ほうがいい
For advice to avoid something: Verb (negative) + ほうがいい
In our sentence, 替えたほうがいい means “you’d better switch (to energy-saving appliances).”

Could we use another conditional like たら or と here? How would the nuance change?

たら: 電気代が高かったら、～ほうがいい。
Feels slightly more neutral or based on “if/when that actually happens.”
と: 電気代が高いと、省エネ家電に替えたほうがいい。
Suggests a general, almost automatic outcome or rule.
Using なら emphasizes “given what we’ve established (that the bill is high), here’s the suggestion,” making it a bit more conversational when responding to new information.

What’s the difference between the verbs 替える, 換える, and 変える?

All three read かえる and can mean “to change,” but their typical uses differ:

替える: replace one thing with another (e.g., 替え玉, currency exchange contexts).
換える: exchange or swap, often used for currencies, data, air (換気), etc.
変える: transform or alter (e.g., 服装を変える, イメージを変える).
For “switching appliances,” 替える or 換える is common. In everyday writing, they’re sometimes used interchangeably, but 変える is less precise for “replace one object with another.”