diff --git a/pkg/config/spec.go b/pkg/config/spec.go
index 05ef4c7..f954fcc 100644
--- a/pkg/config/spec.go
+++ b/pkg/config/spec.go
@@ -565,8 +565,27 @@ func ReadUkiResetSpecFromConfig(c *Config) (*v1.ResetUkiSpec, error) {
 }
 
 func NewUkiInstallSpec(cfg *Config) (*v1.InstallUkiSpec, error) {
+	var activeImg v1.Image
+
+	isoRootExists, _ := fsutils.Exists(cfg.Fs, constants.IsoBaseTree)
+
+	// First try to use the install media source
+	if isoRootExists {
+		activeImg.Source = v1.NewDirSrc(constants.IsoBaseTree)
+	}
+	// Then any user provided source
+	if cfg.Install.Source != "" {
+		activeImg.Source, _ = v1.NewSrcFromURI(cfg.Install.Source)
+	}
+	// If we dont have any just an empty source so the sanitation fails
+	// TODO: Should we directly fail here if we got no source instead of waiting for the Sanitize() to fail?
+	if !isoRootExists && cfg.Install.Source == "" {
+		activeImg.Source = v1.NewEmptySrc()
+	}
+
 	spec := &v1.InstallUkiSpec{
 		Target: cfg.Install.Device,
+		Active: activeImg,
 	}
 
 	// Calculate the partitions afterwards so they use the image sizes for the final partition sizes
@@ -595,8 +614,21 @@ func NewUkiInstallSpec(cfg *Config) (*v1.InstallUkiSpec, error) {
 		Flags:           []string{},
 	}
 
-	err := unmarshallFullSpec(cfg, "install", spec)
-	// TODO: Get the actual source size to calculate the image size and partitions size for at least 3 UKI images
+	// Get the actual source size to calculate the image size and partitions size
+	size, err := GetSourceSize(cfg, spec.Active.Source)
+	if err != nil {
+		cfg.Logger.Warnf("Failed to infer size for images, leaving it as default size (%sMb): %s", spec.Partitions.EFI.Size, err.Error())
+	} else {
+		// Only override if the calculated size is bigger than the default size, otherwise stay with 15Gb minimum
+		if uint(size*3) > spec.Partitions.EFI.Size {
+			spec.Partitions.EFI.Size = uint(size * 3)
+		}
+	}
+
+	cfg.Logger.Infof("Setting image size to %dMb", spec.Partitions.EFI.Size)
+
+	err = unmarshallFullSpec(cfg, "install", spec)
+
 	// Add default values for the skip partitions for our default entries
 	spec.SkipEntries = append(spec.SkipEntries, constants.UkiDefaultSkipEntries()...)
 	return spec, err
diff --git a/pkg/types/v1/config.go b/pkg/types/v1/config.go
index ecbf2a1..7e29666 100644
--- a/pkg/types/v1/config.go
+++ b/pkg/types/v1/config.go
@@ -504,6 +504,7 @@ type DockerImageMeta struct {
 }
 
 type InstallUkiSpec struct {
+	Active          Image               `yaml:"system,omitempty" mapstructure:"system"`
 	Target          string              `yaml:"device,omitempty" mapstructure:"device"`
 	Reboot          bool                `yaml:"reboot,omitempty" mapstructure:"reboot"`
 	PowerOff        bool                `yaml:"poweroff,omitempty" mapstructure:"poweroff"`
diff --git a/pkg/uki/install.go b/pkg/uki/install.go
index 5eb098f..89071b2 100644
--- a/pkg/uki/install.go
+++ b/pkg/uki/install.go
@@ -33,55 +33,6 @@ func (i *InstallAction) Run() (err error) {
 	_ = utils.RunStage(i.cfg, "kairos-uki-install.pre")
 	_ = events.RunHookScript("/usr/bin/kairos-agent.uki.install.pre.hook")
 
-	// immucore mounts CDROM under this path
-	_, err = i.cfg.Fs.Stat(constants.UkiCdromSource)
-	if err != nil {
-		i.cfg.Logger.Errorf("mountpoint '%s' not ready. error: %s", constants.UkiCdromSource, err)
-		return err
-	}
-	// Get source (from spec?)
-	// If source is empty then we need to find the media we booted from....to get the efi files...
-	// cdrom is kind fo easy...
-	_ = fsutils.MkdirAll(i.cfg.Fs, constants.UkiSource, os.ModeDir|os.ModePerm)
-
-	image := &v1.Image{
-		File:       filepath.Join(constants.UkiCdromSource, "efiboot.img"),
-		Label:      "UKI_SOURCE", // Made up, only for logging
-		MountPoint: constants.UkiSource,
-	}
-
-	mounted, err := i.cfg.Mounter.IsMountPoint(constants.UkiCdromSource)
-	if !mounted || err != nil {
-		err = e.MountImage(image)
-		if err != nil {
-			return err
-		}
-	}
-
-	cleanup.Push(func() error {
-		return e.UnmountImage(image)
-	})
-
-	source := v1.NewDirSrc(constants.UkiSource)
-
-	// Get the actual source size to calculate the image size and partitions size
-	size, err := config.GetSourceSize(i.cfg, source)
-	if err != nil {
-		i.cfg.Logger.Warnf("Failed to infer size for images, leaving it as default size (%sMb): %s", i.spec.Partitions.EFI.Size, err.Error())
-	} else {
-		// Only override if the calculated size is bigger than the default size, otherwise stay with 15Gb minimum
-		if uint(size*3) > i.spec.Partitions.EFI.Size {
-			i.spec.Partitions.EFI.Size = uint(size * 3)
-		}
-	}
-
-	i.cfg.Logger.Infof("Setting image size to %dMb", i.spec.Partitions.EFI.Size)
-
-	// Create EFI partition (fat32), we already create the efi partition on normal efi install,we can reuse that?
-	// Create COS_OEM/COS_PERSISTANT if set (optional)
-	// I guess we need to set sensible default values here for sizes? oem -> 64Mb as usual but if no persistent then EFI max size?
-	// if persistent then EFI = source size * 2 (or maybe 3 times! so we can upgrade!) and then persistent the rest of the disk?
-
 	// Deactivate any active volume on target
 	err = e.DeactivateDevices()
 	if err != nil {
@@ -123,7 +74,7 @@ func (i *InstallAction) Run() (err error) {
 	}
 
 	// Copy the efi file into the proper dir
-	_, err = e.DumpSource(i.spec.Partitions.EFI.MountPoint, source)
+	_, err = e.DumpSource(i.spec.Partitions.EFI.MountPoint, i.spec.Active.Source)
 	if err != nil {
 		return err
 	}