Learn Hardcore Esperanto: Mia familio loĝas en malnova domo, sed nia hejmo estas tre varma. - My family lives in an old house, but our home is very warm.

Mia familio loĝas en malnova domo
= My family lives/resides in an old house. (talking about where they live)
Mia familio vivas feliĉe
= My family lives happily. (talking about how they live, not where)
Mia familio estas en la domo
= My family is in the house. (location at this moment, not their residence)

Using loĝas is the most natural way to say “lives (resides) in” a place.

What’s the difference between domo and hejmo?

domo = house, building where people live (physical structure)
hejmo = home in the emotional/relational sense (where you feel at home)

So the contrast in the sentence is intentional:

…loĝas en malnova domo – the building is old
sed nia hejmo estas tre varma – but our home (the atmosphere, feeling) is very warm

You could live in a new apartment (nova apartamento) but still say:

Tio estas mia hejmo = That is my home (emotionally).

Why is it Mia familio but nia hejmo? Why not mia hejmo too?

Grammatically, both mia hejmo (my home) and nia hejmo (our home) are possible.

In this sentence:

Mia familio = my family (from the speaker’s viewpoint)
nia hejmo = our home (the shared home of all family members)

So the speaker is:

talking about their family as my family
describing the home as belonging to the whole group, our home

It’s a natural and common shift in perspective, not a grammatical requirement.

Why is there no -n (accusative) ending on any of the words? Shouldn’t en malnova domo take -n?

The -n (accusative) ending is mainly for:

direct objects
showing motion into/onto/through with some prepositions

Here:

Mia familio is the subject.
There is no direct object of loĝas or estas.
en malnova domo expresses location (“in an old house”), not movement into it.

So:

Mia familio loĝas en malnova domo.
(location → no -n)
Mia familio iras en malnovan domon.
My family goes into an old house. (movement into → domon with -n)

That’s why there is no -n in the original sentence.

Why is it en malnova domo and not en la malnova domo?

Esperanto has a single definite article: la = the.

You use la when you’re talking about some specific, identifiable house:

Mia familio loĝas en la malnova domo apud la preĝejo.
= My family lives in the old house near the church.

Without la, it’s more general:

Mia familio loĝas en malnova domo.
= My family lives in an old house. (no special house the listener is supposed to already know about)

So the sentence as given corresponds to English “an old house”, not “the old house.”

Why do the adjectives end in -a, like malnova and varma?

In Esperanto, all adjectives end in -a in their basic (singular, non‑accusative) form.

malnova domo = old house
- malnov- (root “old”) + -a (adjective)
varma hejmo = warm home
- varm- (root “warm”) + -a (adjective)

The pattern:

nouns: -o → domo, hejmo, familio
adjectives: -a → malnova, varma
verbs (present): -as → loĝas, estas

Do adjectives have to agree with the noun in number (and case)? What would the plural be?

Yes. Adjectives agree with their noun in:

number: singular -a, plural -aj
case (accusative): add -n if the noun has -n

Examples:

singular: malnova domo = an old house
plural: malnovaj domoj = old houses

With motion (accusative):

Ili eniras en malnovan domon.
Ili eniras en malnovajn domojn.

In your sentence, domo and hejmo are singular and not accusative, so:

malnova domo
tre varma hejmo

Does word order matter? Could I say Nia hejmo estas tre varma, sed mia familio loĝas en malnova domo instead?

Basic Esperanto word order is S–V–O (subject–verb–object), like English, but it is fairly flexible.

Your alternative:

Nia hejmo estas tre varma, sed mia familio loĝas en malnova domo.

is perfectly grammatical. The original order just puts the “old house” idea first and then contrasts it with the warm home. Swapping the clauses only changes emphasis and flow, not correctness.

What exactly does sed mean, and how is it different from words like kaj or tamen?

sed = but (introduces contrast)
kaj = and (adds information)
tamen = however, nevertheless (usually adverb, not a conjunction)

Your sentence:

…, sed nia hejmo estas tre varma.
= …but our home is very warm.

You could also say:

Mia familio loĝas en malnova domo. Tamen nia hejmo estas tre varma.
Two sentences; tamen works like “however.”

But sed is the most natural direct equivalent of “but” joining two clauses.

Is varma here about physical warmth or emotional warmth?

varma literally means warm (in temperature), but in context with hejmo it very often also suggests emotional warmth, coziness, friendliness.

So nia hejmo estas tre varma can be understood as:

The home is literally warm (not cold, well heated), and/or
The home feels warm and welcoming, not cold emotionally.

Esperanto allows that same metaphorical use, much like English does.

Why is the sentence Mia familio loĝas en malnova domo, sed nia hejmo estas tre varma and not something like Mia familio estas en malnova domo?

esti en (“to be in”) describes being located somewhere at a moment:

Mia familio estas en malnova domo.
= My family is in an old house (right now).

loĝi en describes residing/living there:

Mia familio loĝas en malnova domo.
= My family lives in an old house (that’s their home address).

The sentence is talking about where they live, not just where they are right now, so loĝas is the precise and most idiomatic choice.