Water HeatersSolar with Electric Backup
MC Green B80-20 Water Heater Manual
Setup, everyday use, maintenance and troubleshooting for the solar water heater with electric backup, with verified specifications.
- Collector area36.2 sq. ft.
- Solar tank80 gal.
- Freeze limit29 °F
About the MC Green B80-20
MC Green model B80-20 (SWH) is a solar water heater with electric backup that meets ENERGY STAR efficiency requirements.
This direct thermosyphon system combines 36.2 sq. ft. of flat-plate collector area, an 80-gallon solar storage tank, and a tank-type backup heater (1.5 kW element). It is certified to SRCC OG-300 under number 30004360. The DOE classifies it in the low usage draw pattern, so its efficiency rating assumes about 38 gallons of hot water a day.
Specifications
| Brand | MC Green |
|---|---|
| Model number | B80-20 |
| Model name / series | SWH |
| Water heater type | Solar with Electric Backup |
| Fuel / energy source | Electric |
| DOE draw pattern | Low-Usage |
| Voltage | 240 V |
| Solar system type | Direct Thermosyphon |
| Collector type | Flat Plate |
| Collector area | 36.2 sq. ft. |
| Solar storage tank | 80 gal. |
| Backup heater type | Tank |
| Backup element input | 1.5 kW |
| Freeze tolerance limit | 29 °F |
| SRCC OG-300 certification no. | 30004360 |
| Connected / demand-response capable | No |
Safety information
- Set the water heater to about 120 °F (49 °C). Water at 140 °F can cause a serious burn in a few seconds; at 120 °F it takes several minutes. Homes with young children or older adults benefit from anti-scald valves at tubs and showers.
- The temperature and pressure (T&P) relief valve protects the tank from bursting. Never cap, plug or remove it, and keep its discharge pipe running full size to within about 6 in. of the floor or to an approved drain.
- Installation should be done by a licensed plumber (and electrician or gas fitter where required). Most jurisdictions require a permit.
- Turn off the breaker before removing any cover. Never switch on power to an electric water heater until the tank is completely full — an element energized in air burns out in seconds.
- Where local code requires it (for example, in seismic zones), secure the tank to the wall with approved strapping.
- Solar collectors and piping can become hot enough to cause severe burns, and roof work carries a serious fall risk. Leave collector service to a qualified solar installer.
Installation and first-time setup
Use this checklist when planning the installation of the MC Green B80-20 and when reviewing the finished job with your installer.
- Install the certified configuration
Solar water heaters are rated as complete systems. Install the collectors, tank, backup heater and controls that make up the SRCC OG-300 certified configuration (30004360); substitutions can change performance and incentive eligibility.
- Collector siting
In the continental U.S., collectors generally face south (within about 45°) with a tilt near the site latitude and little shading from 9 a.m. to 3 p.m. Have the roof structure checked for the added weight and flash all penetrations carefully.
- Freeze protection
This system's freeze tolerance limit is 29 °F. Keep antifreeze or drain-down protection in good order to maintain that rating.
- Mixing valve and backup
Solar-heated water can exceed safe tap temperatures on sunny days, so install a thermostatic mixing valve. Connect and set the backup heater per the manual.
- Plumbing connections
Use dielectric fittings where dissimilar metals meet, install a shut-off valve on the cold inlet, and pipe the relief valve discharge to an approved location. Add an expansion tank if the supply has a check valve or pressure-reducing valve.
- Fill and purge before start-up
Fill the tank completely and run a hot tap until water flows steadily, so no air remains, before turning on power. Then set the temperature and check every joint for leaks.
Using your water heater
Living with solar hot water
On sunny days the collectors do most of the work and the backup heater rarely runs; in cloudy weather and winter the backup makes up the difference. Run dishwashers and laundry in the afternoon or early evening, when the solar tank is hottest, and set the backup thermostat no higher than you need.
This passive design circulates water without a pump, so there is little to adjust, but the rooftop tank or collector must stay within its freeze tolerance.
Saving hot water and energy
- Fix dripping hot-water taps promptly and use WaterSense showerheads and faucet aerators.
- Insulate the first several feet of hot and cold pipes at the heater.
- Wash laundry in cold water when possible.
Care and maintenance
| When | What to do |
|---|---|
| Every year | Test the T&P relief valve by lifting its lever briefly with a bucket under the discharge pipe; if it does not reseat and stop dripping, have it replaced. |
| Every year | Drain a few gallons from the tank drain valve, or flush it fully, to remove sediment — more often in hard-water areas. |
| Every 2–3 years | Have the anode rod inspected and replaced when it is heavily corroded; this is the main defense against tank corrosion. (Some models use a powered anode — follow the manual.) |
| Every year | Inspect collectors, glazing, mounting and roof penetrations; check for leaks and confirm the controller and pump operate correctly. |
Troubleshooting
Check these common causes before calling for service.
| Problem | Possible cause | What to try |
|---|---|---|
| Backup heater runs on sunny days | Controller or sensor fault; pump not running; air or low fluid in the loop; shaded collectors. | Check the controller display and the pump; call the solar installer for loop service. |
| Water too hot at taps | Mixing valve missing, set too high or failed. | Have a thermostatic mixing valve installed or adjusted. |
| Rotten-egg smell in hot water | Bacteria reacting with the anode rod or water chemistry. | Flush the tank; a plumber can replace the anode with a different alloy or treat the water. |
| Relief valve dripping or discharging | Excess pressure from thermal expansion; failing valve; temperature set too high. | Have the pressure checked and an expansion tank added if needed; replace a faulty valve. Never plug it. |
Energy use and running costs
The certification record does not include a usable SUEF value for this system, so we cannot estimate its backup energy use. Ask the installer for the SRCC OG-300 rating sheet, which lists the system's modeled savings for your location.
Frequently asked questions
Is the MC Green B80-20 freeze tolerant?
Its freeze tolerance limit is 29 °F.
What is the SRCC certification number for the MC Green B80-20?
It is certified to SRCC OG-300 under number 30004360. Many incentive programs ask for this number.
What type of solar system is the MC Green B80-20?
It is listed as a direct thermosyphon system with flat-plate collectors. In a direct system, household water itself flows through the collectors, so it is best suited to mild climates and good water quality. It circulates passively, without a pump.
What backup heater does the MC Green B80-20 use?
It uses a tank-type electric backup heater and a 1.5 kW element, which heats water whenever solar energy is not enough.
Is the MC Green B80-20 ENERGY STAR certified?
Yes. It appears on the ENERGY STAR certified water heater list, with a certification date of September 2021.
Sources and disclaimer
Specifications on this page come from the ENERGY STAR certified water heaters dataset published by the U.S. Environmental Protection Agency (record certified September 13, 2021), retrieved October 7, 2026.
The setup, operating, maintenance and troubleshooting guidance is written by ManualHarbor's editors for this specific product type and configuration. It is an independent guide — not a reproduction of the manufacturer's manual — and ManualHarbor is not affiliated with MC Green. Always follow the safety instructions, installation requirements and warranty terms supplied with your unit, and contact MC Green or an authorized service provider for warranty repairs and replacement parts.
Running-cost figures use assumed U.S. average utility prices and are estimates for comparison only. See our editorial methodology for details.
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