Doug Mossbrook
Yes, it’s technically possible, but the answer is NO.
We had a customer write in saying “At my IGSHPA training the instructor told us that using geothermal with baseboard radiant absolutely could be done -because the plumbers used to always oversize the baseboard runs anyway -maxing them out per room -so the lower 120 degree water temp would work. I would like to know what the engineers up your way say about this.”
The short answer is no, don’t use geothermal with baseboard heating or radiators.
The longer answer is yes, but with a few caveats that will be explained here. Baseboard heaters use convection heating to heat a room. There are typically fins inside the heater called elements. These elements have a set resistance, which transfers heat energy from the hot water and dissipates it in the form of heat to the surrounding air.
Because the warm air is lighter than the cooler air, it rises out of the top of the heater and the cooler air closer to the floor is drawn in from the bottom to replace the displaced warm air. This is convection. This cycle continues until the air surrounding your control center or thermostat reaches the specified temperature.
Convection
The typical operating temperature of water in a baseboard heating system is roughly 160 – 180 degrees fahrenheit. This high temperature is critical to be as efficient as possible.
Convection does not work with low temperature water from a geothermal heat pump.
And as we all know, a geothermal system is a low temperature heat source, with a maximum output temperature of roughly 115 degrees. With radiant floor heating or forced air, this water temperature is perfect to heat a room, and it helps keep the geo system as efficient as possible.
115 degree water is not hot enough to adequately dissipate heat for baseboard hydronic systems. It will dissipate some heat through the fins simply because the water in the pipes is warmer than the room; however, to heat a room to 70 degrees will take a long time, require a lot of energy, and additional surface area (more radiators).
The technical answer whether or not baseboard radiant works with geothermal is yes; however the cost of additional radiators, piping, and reduced efficiency make the correct answer no. Baseboard radiant is most efficient when incorporated with a boiler system. A boiler radiant heating system is capable of much higher output temperatures than a geothermal system.
Water heater recovery is measured in gallons per hour. Flow rates for a radiant system can be calculated at 1 gallon per minute for each 10,000 BTUH of heat loss. Due to recovery time, water heaters will work only with very small radiant systems. Larger radiant systems can use water heaters but it is essential to correctly calculate heat loss and select equipment based on recovery time for a 20 degree temperature differential.
