How HeatSync compares
This page compares HeatSync to the other options in the same problem space. The goal is honest framing — these products serve different shapes of user, and the right answer for you depends on what you actually want.
We didn’t build this page to argue HeatSync wins on every axis. It doesn’t. Specifically: Homely and Havenwise offer cloud-side predictive optimisation that HeatSync doesn’t (yet) match. And OpenEnergyMonitor delivers genuine metrology-grade CoP measurement that no software-only project running off the bus could substitute for — if you need a real number for an MCS report or a tariff dispute, that’s the tool. These are complementary in many setups, not competitors.
Facts current as of May 2026. Spotted something out-of-date? Open an issue on GitHub.
At a glance
Section titled “At a glance”| Cloud required? | Control | Samsung interface | Home Assistant | Up-front | Sub | Open source | Tariff / carbon | |
|---|---|---|---|---|---|---|---|---|
| HeatSync | No | R+W (incl. FSV via F3/F4 experiment) | F1/F2 native; F3/F4 WIP | Native MQTT auto-discovery, ~25 entities | ~£25 | £0 | Yes (MIT) | Built-in — tariff windows + UK grid-carbon-aware DHW + schedule heatmap |
| esphome_samsung_hvac_bus | No | R+W (partial; FSV partial) | F1/F2 | Native ESPHome | ~£15–£30 (DIY) | £0 | Yes (GPL) | None (HA automations) |
| 70p4z/samsung-nasa-mqtt | No | R+W via wired-remote impersonation | F3/F4 (Python on Pi + THVD8000) | Via MQTT | ~£40–£60 | £0 | Yes | None |
| OpenEnergyMonitor (emonHP) | Optional | Read-only monitoring | Neither — CT clamps + MID-class flow meter | Via emoncms HTTP / MQTT | £462+VAT (≤10 kW), £539+VAT (≤17 kW) | £0 self-host; ~£1–3/mo emoncms.org | Yes (HW + FW) | None (it’s a meter) |
| Samsung MIM-H04EN | Yes — SmartThings | R+W: on/off, mode, target, DHW boost, schedules | F1/F2 | None (cloud-only) | ~£150–£220 + fit | £0 | Proprietary | None |
| Homely | Yes | R+W via Samsung MIM-B19N Modbus board | Indirect (Modbus, not NASA) | None | ~£399–£549 | £0 first 2 yr, then ~£2/mo | Proprietary | Strong — weather-forecast predictive, Agile/Cosy/Go-aware |
| Havenwise | Yes | R+W via vendor cloud APIs | Indirect (Samsung cloud, not bus) | None | £0 — app-only | £7/mo (1-mo trial) | Proprietary | Tariff-aware load-shift, multi-brand |
| Planet Devices “Atmo” | Yes | R+W via Samsung MIM-B19N | Indirect | None public | Installer-priced | Yes, opaque | Proprietary | Not a headline feature |
Footnotes:
- MIM-H03 is discontinued — current Samsung NASA Wi-Fi adapter is the MIM-H04EN.
- The Samsung MIM-B19N is Samsung’s own Modbus-to-NASA bridge board (~£200). Homely, Havenwise’s Samsung path, and Planet Devices all attach via this board rather than directly tapping the NASA bus.
- We’ve left out Tado, Hive and MELCloud — they’re generic thermostats or vendor cloud apps, not heat-pump-native enough to compare like-for-like.
Where each fits
Section titled “Where each fits”HeatSync
Section titled “HeatSync”Best for: someone who wants local-first control, has (or doesn’t mind acquiring) a small soldering / Wi-Fi config skillset, runs Home Assistant or plans to, and is comfortable with software that’s still on a v0.8 trajectory.
Honest caveat: HeatSync doesn’t have cloud-side predictive
optimisation. Today the /insights heat-loss analyser surfaces the
building’s U-value + time constant; tomorrow that should feed into
auto-tuned flow temperatures, but it doesn’t yet. If you want
set-it-and-forget-it weather-forecast preheat, look at Homely or
Havenwise.
esphome_samsung_hvac_bus
Section titled “esphome_samsung_hvac_bus”Best for: existing ESPHome users who already trust the ecosystem and want the lightest-touch local NASA bridge. Active maintenance, big install base. Our own NASA parser was vendored from this project with attribution preserved.
70p4z/samsung-nasa-mqtt
Section titled “70p4z/samsung-nasa-mqtt”Best for: someone who wants F3/F4 wired-remote bus access today on a Raspberry Pi rather than ESP32. We’re a kindred project here — our F3/F4 experiment is converging on the same architectural pattern (impersonating a wired remote to write FSV registers that don’t broadcast on F1/F2).
OpenEnergyMonitor
Section titled “OpenEnergyMonitor”A genuinely brilliant project run by a small team in Wales — open-source hardware, open-source firmware, and a UK heat-pump community dataset at heatpumpmonitor.org that has done more for honest CoP reporting than any vendor. The emonHP bundle gives you MID-class flow metering, dedicated CT clamps, properly calibrated temperature probes — metrology, not estimation.
HeatSync computes a calorimetric COP from the bus’s own flow + ΔT readings, which is good enough to watch trends and spot regressions but isn’t a substitute for proper instrumentation. If you care about the absolute number — for an MCS report, a tariff dispute, or publishing your numbers — emonHP is the right tool.
The bundle price reflects what’s in the box (the MID flow meter alone isn’t cheap, and that’s just physics). For most enthusiasts that’s significant up-front money, which is the main reason it doesn’t end up in every install. If you do invest, it pairs beautifully with HeatSync — emonHP for measurement, HeatSync for control, both local, both exporting to Home Assistant.
Samsung MIM-H04EN
Section titled “Samsung MIM-H04EN”Best for: someone who wants Samsung’s officially supported path, doesn’t mind a Samsung account + Wi-Fi-required setup, and is happy with the basic on/off / target / DHW boost control surface.
Honest caveat: cloud-locked, no FSV access, breaks if Samsung’s cloud ever shuts down. The MIM-H03 (its predecessor) being discontinued in 2024 should give pause about long-term commitment.
Homely
Section titled “Homely”Best for: someone who wants the smartest possible thermostat with zero maintenance and no DIY. Genuinely strong predictive logic — they ingest Met Office forecasts and Agile/Cosy/Go tariff schedules and write setpoints with no homeowner intervention.
Honest caveat: cloud-locked, attaches to Samsung via the third- party MIM-B19N Modbus board (not the NASA bus directly), £2/mo subscription after year 2.
Havenwise
Section titled “Havenwise”Best for: app-only setup with no hardware to install — works entirely via the manufacturer’s existing cloud APIs (Samsung, Vaillant, Mitsubishi, Daikin early access). The cheapest entry into predictive optimisation if you already have a SmartThings-connected Samsung.
Honest caveat: requires your heat pump to already be cloud-paired via its OEM app, £7/mo (highest sub in this list), and you’re stacking two clouds (Samsung + Havenwise) which is more failure points than a local-only stack.
Planet Devices “Atmo”
Section titled “Planet Devices “Atmo””Best for: installers managing a fleet of heat pumps across brands who want a single dashboard for diagnostics and remote troubleshooting. Not really aimed at homeowners.
Honest caveat: opaque retail pricing, no public Home Assistant story, sub model not publicly listed.
So which should you actually pick?
Section titled “So which should you actually pick?”Roughly:
- I want local control, hackable, free, willing to DIY: HeatSync or esphome_samsung_hvac_bus. Pick HeatSync if you want the carbon / tariff scheduling built-in; pick the ESPHome project if you already use ESPHome and prefer its entity model.
- I want set-it-and-forget-it cloud optimisation, don’t mind paying: Homely (best predictive, hub + node) or Havenwise (app-only, cheaper to start, more brands).
- I want metrology-grade CoP numbers: OpenEnergyMonitor’s emonHP. Run alongside any of the above.
- I want Samsung’s official path and nothing else: MIM-H04EN.
Nothing in this list strictly dominates the others on every axis. HeatSync is the closest thing to “free, local, open, with built-in tariff awareness” — but if you want learned weather-comp without ever touching a config screen, the cloud-based predictive products are genuinely good at that.