diff --git a/esphome/core/__init__.py b/esphome/core/__init__.py
index 983b844ced..bc9a070e83 100644
--- a/esphome/core/__init__.py
+++ b/esphome/core/__init__.py
@@ -703,7 +703,7 @@ class EsphomeCore:
     def platformio_cache_dir(self) -> str:
         """Get the PlatformIO cache directory path."""
         # Check if running in Docker/HA addon with custom cache dir
-        if cache_dir := os.environ.get("PLATFORMIO_CACHE_DIR"):
+        if (cache_dir := os.environ.get("PLATFORMIO_CACHE_DIR")) and cache_dir.strip():
             return cache_dir
         # Default PlatformIO cache location
         return os.path.expanduser("~/.platformio/.cache")
diff --git a/tests/unit_tests/test_core.py b/tests/unit_tests/test_core.py
index b36bc8f4c0..4677140ad2 100644
--- a/tests/unit_tests/test_core.py
+++ b/tests/unit_tests/test_core.py
@@ -687,6 +687,14 @@ class TestEsphomeCore:
             expected = os.path.expanduser("~/.platformio/.cache")
             assert target.platformio_cache_dir == expected
 
+    def test_platformio_cache_dir_whitespace_env_var(self):
+        """Test platformio_cache_dir with whitespace-only env var falls back to default."""
+        target = core.EsphomeCore()
+
+        with patch.dict(os.environ, {"PLATFORMIO_CACHE_DIR": "   "}):
+            expected = os.path.expanduser("~/.platformio/.cache")
+            assert target.platformio_cache_dir == expected
+
     def test_platformio_cache_dir_docker_addon_path(self):
         """Test platformio_cache_dir in Docker/HA addon environment."""
         target = core.EsphomeCore()