Faults hide in plain sight
A heat pump with the wrong refrigerant charge or choked airflow still heats and cools. It just does it worse, at a higher bill, and nothing on the wall tells the homeowner.
Pre-seed · Spun out of Southern Heat Pumps · Building for the whole US
Read any heat pump’s physics from the outside.
Coilwise is a low-cost clamp-on sensor kit and a physics-informed AI model, built as one system. It goes on any brand of heat pump or heat-pump water heater in about an hour, with no refrigerant gauges and no manufacturer data. It finds charge and airflow faults, estimates live efficiency, and then runs the unit as a flexible load for the grid.
We’re new and pre-revenue. Right now we want two kinds of conversation: with seed investors, and with the first contractors, utilities and manufacturers willing to put kits on real units.
01The problem
Heat pumps are going into millions of homes. After install day, it’s hard for anyone to see how they’re really running.
Diagnosis needs a truck and gauges
Confirming charge today means a technician on site, gauges on the service ports, and years of experience to read them. That doesn’t scale to millions of new units.
Data is locked to one brand
Where connected diagnostics exist, they belong to one manufacturer’s newer equipment. Contractors and utilities work with every brand and every age of unit.
Flexibility can’t be verified
Utilities want heat pumps and water heaters to soak up cheap midday power and back off at the evening peak. To pay for that, they need to know what each unit actually did, and whether it was healthy enough to ask.
02Why now
Three shifts are landing at the same time.
Millions of homes are moving onto heat pumps.
Heating, cooling and hot water across the US are shifting from combustion to heat pumps. That puts millions of new machines in homes, and each one only performs as well as it was installed and maintained.
The federal water-heater rule takes effect.
The federal efficiency rule for residential water heaters takes effect in 2029. For most electric tank water heaters, meeting it means a heat pump, and every one of those comes with a tank that can store energy as heat.
Grids need demand that can move.
As solar grows, grids can have more power than they need at midday and too little in the evening. A heat pump that can be scheduled, verified and kept healthy is exactly the kind of load that can move.
03The insight
Measure the gap, not the gas.
Behind this text is a refrigerant’s equation of state. The flat valley is where liquid and vapor coexist, and that’s where a heat pump does its work: boil cold refrigerant at low pressure, compress it, condense it hot at high pressure, and let it expand back down.
Given the weather, the load and the power draw, physics says where a healthy unit’s loop should sit. That’s the dashed line. On a healthy unit the real loop sits right on top of it.
(p + 3/v²)(3v − 1) = 8T van der Waals, reduced units. Maxwell’s equal-area rule flattens the shaded loop into the boiling line.
- measured cycle
- model’s expectation
- liquid–vapor dome
A fault pulls the loop off its path, in a direction you can name.
Our kit never opens the refrigerant circuit. Pipe temperatures, true power and air conditions pin down where the real loop is. The gap between that and the model’s expectation, the residual, stays near zero on a healthy unit and points somewhere specific when something is wrong. The same measurements give a live estimate of efficiency (COP).
Undercharge: superheat ↑ · subcooling ↓ · power ↓
r = ymeasured − ŷ(weather, load; θ) every channel, at matched conditions
Anything that doesn’t match a known signature is flagged as unknown instead of being forced into a label.
One backbone. A small adapter for each brand.
In 1880 van der Waals noticed that very different fluids, once scaled by a few constants, fall onto nearly the same surface. Our model is built the same way: one shared physics backbone, plus a handful of per-brand parameters such as probe offsets, the compressor map and the fan curve.
Taking on a new brand means fitting those few numbers from a handful of examples. We don’t retrain from scratch.
ŷ = fshared(x; θbrand) θbrand: a few numbers per brand family
04How it works
One kit, one model, about an hour on site.
- 1
Clamp on
Split-core current clamps, a plug-in voltage reference, pipe and air probes, and an optional vibration sensor. Nothing is cut, opened or tapped into the refrigerant circuit, and it fits any brand of heat pump or heat-pump water heater.
- 2
Learn the unit
The installer runs the unit through a few steady states. The model fits that unit’s small set of parameters and stores its healthy baseline.
- 3
Watch and act
From then on it scores residuals continuously, estimates COP, flags charge and airflow faults, and, while the unit is healthy, runs it as a flexible load.
- 1
Current clamps
Split-core, around one conductor at the outdoor unit and at the blower or water-heater branch. For start-up transients, short-cycling, and telling the compressor apart from the blower or backup element.
- 2
True power and voltage
A plug-in voltage reference. For real kilowatts and power factor: the bottom half of the efficiency ratio, and proof of every kilowatt shifted.
- 3
Pipe surface temperatures
Strapped to bare copper and insulated, or to the tank wall on a water heater. For superheat and subcooling, the core charge signals, and the tank’s state of charge.
- 4
Air temperature and humidity
Return, supply and outdoor air. For delivered capacity, and for the weather that every expectation depends on.
- 5
Vibration (optional)
On the compressor shell or fan bracket. For fan and bearing wear, before it shows up in the current.
Every sensor is there because a term in the model needs it. The physics decides what we measure.
At the unit
An edge node meters power, runs the model, enforces safety rules and talks to the equipment. It keeps working if the Wi-Fi drops.
In the cloud
Fleet training, per-brand adapters and scheduling. Compact features go up, not raw streams, and signed model updates come down.
Safety first
It never asks a unit that looks unhealthy to take on extra load, and it respects each unit’s comfort band and low-temperature limits.
05The grid
A water-heater tank is a battery that stores heat.
A shower draws more power than a home heat pump can deliver on demand, so heat-pump water heaters already keep a tank of hot water. That makes them schedulable: charge the tank when power is cheap or the sun is high, then coast through the evening peak.
- CTA-2045 at the unit. The edge node sends Load Up, Shed and Return to Normal through the standard port and reads back what the equipment did. Equipment without a port falls back to thermostat setpoint offsets.
- Health-gated. The same model that watches the unit decides when it’s safe to shift. Hot-water minimums, comfort bands and low-temperature limits are hard constraints.
- Measured, not modeled. Every kilowatt shifted is counted by the same clamps that diagnose the unit.
ut = min(&ubar;, max(0, λ − Lt)) water-filling: the exact solution for spreading a tank’s charge under a load curve
Eastern tank
Idle
Tap a ring to pick a time zone. Drag around the dial to scrub the day.
All four zones, summedno schedule
06The market
Every heat pump in the country, whatever the brand.
Our market is the installed and soon-to-be-installed base of heat pumps and heat-pump water heaters across the US, and the people responsible for them. A kit that works on any brand and is cheap enough to leave on the unit can reach that base without waiting for every manufacturer to connect its own.
HVAC contractors
See problems before the callback. Commission with evidence, arrive with a diagnosis, and stay connected to the customer after install day.
Utilities and programs
Measured, verifiable flexibility from equipment that’s already in homes, plus install-quality checks for incentive programs.
Manufacturers
Field performance and fault data from units in homes, including models with no connectivity, and a path into grid programs.
Homeowners
Equipment that runs the way it should and fewer surprises, delivered through their contractor or utility rather than another app to manage.
We start close to the install. The company is spinning out of Southern Heat Pumps, a heat-pump installer, and the kit is designed around how technicians actually work on site.
07Team
The founders
Robert Stevens
Co-founder
Russell Stevens
Co-founder
We’re spinning Coilwise out of Southern Heat Pumps as its own company, to build this for heat pumps across the country.
- Designed
The full system. Signal chain, physics-informed model, edge and cloud split, control interface, and a prototype bill of materials.
- Next
A fault-injection rig. Real units with known charge, airflow and restriction faults, measured by the kit alongside reference instruments.
- Then
Kits in the field. First units with design partners, across brands and climates.
- Status
Pre-revenue, no customers yet. Finding the first ones is what this page is for.
08The ask
Request a conversation.
Investors
We’re meeting seed investors who back hardware-plus-AI companies early. If that’s you, we’d like to walk you through the system design and our plan to prove it on real units.
Design partners
HVAC contractors, utilities and program administrators, and manufacturers: we’re looking for a small first group to put early kits on real units and tell us what we got wrong.