Geothermal (Ground Source) Heat Pumps

When considering replacing an existing furnace or boiler, you should realize that another option exists that can significantly reduce heating and cooling costs. A Geothermal Heat Pump can replace many boilers and most furnaces.  We will gladly do a free evaluation of your home to see if this makes sense for you.

At current rates, a Geothermal Heat Pump will save you about 62% over the highest efficiency furnace or boiler.  As gas prices go up, this savings will increase.

Water or Forced Air Geothermal Systems – Geothermal systems come in two main configurations:
Forced air systems that convert energy from the earth into warm air for heating or cool air for cooling.  These are often called ground to air systems.

Water systems that convert energy from the earth into warm (up to 120 degree) water for heating.  These are called ground to water systems and work well in radiant heat applications.
Packaged or Split systems – Forced air geothermal systems can be totally contained in a single equipment cabinet (packaged) that includes the compressor, air coil, water coil and blower motor. OR  it can be configured as a split system which would be hooked up to a furnace much like a normal air conditioner.   A split system uses a furnace’s blower for air movement and its burner as a third, or emergency, heating “stage”.  A packaged system would include an electric heat strip as a third or emergency stage and would completely replace a furnace and air conditioning condenser in a forced air system.

Compressor Stages – A major component of a geothermal system is the compressor.  A geothermal heat pump has either a single or dual stage compressor.  In our climate, it often makes sense to use a two-stage compressor, which allows for heating with both stages and cooling with only the first stage.  This allows for properly sized air conditioning with associated dehumidification.

Domestic Hot Water Assist is another option to consider when purchasing a geothermal system.  This option reduces water heating costs by using excess heat to generate hot water.

Geothermal Loops – Ground source heating systems use a geothermal loop to “pull” energy from the Earth.  Loops can be either closed or open.  In Wisconsin, a closed loop system is the most common.  A closed loop can be either horizontal or vertical.  Horizontal loops are typically less expensive than vertical loops but require more yard or lot area.

Furnaces: Regular or High Efficiency

Furnace efficiency denotes the “split” between the fuel costs that actually heat a home vs. the costs that go ‘up the chimney’ or out the vent pipe.  A 95% efficient furnace uses $95 of every $100 in fuel costs to heat the home.  Contrast that with an old, 60% furnace.  Only $60 of that $100 will be used to heat the home.  $40  will go ‘up the chimney’.  With today’s energy costs, that total dollar loss can be very high.

Highest efficiency equipment may qualify for Focus on Energy rebates and Federal tax credits!  This, combined with fuel savings, may justify the added initial expense IF you are going to be in the home long enough for the payback.

Stainless Steel or Aluminized Primary Heat exchangers.  Stainless steel primary heat exchangers cost more but last longer.  Primary heat exchanger failures are a major cause of having to replace high efficiency furnaces.  Making the additional investment in a furnace that has both primary and secondary stainless steel heat exchangers might make sense.

ECM Blower Motors (variable speed) cost more initially but cost much less to operate.  They allow the homeowner to run the blower continuously while saving money on electrical costs.  This feature also improves air quality and comfort in your home.  These motors are quiet and automatically adjust speed to provide proper air flow in your home.

Two-Stage Gas Valves save money and deliver a more even room temperature by adjusting the output of the furnace to the current heating demand.  A furnace has to be “sized” for the coldest possible day of the year, yet this capacity is needed for less than 10% of the heating season.  A two-stage gas valve starts the furnace in first stage, which runs at 80% of full fire.  (A 75,000 BTU furnace with 2- stage gas valve will start at 60,000 BTUs in first stage.)  If the furnace runs for 10 minutes without “satisfying” the heating requirement, the furnace will automatically change to second stage and run at full fire until the targeted room temperature is achieved.

Boiler Systems

Efficiency Ratings 
Boilers are available in efficiency ratings from 80% to 99%.  Efficiency ratings above 88% are typically only available in “low temperature” applications.  In most cases it may not make sense to pay a premium for a very high efficiency boiler (98%) when the heating application requires 180 degree water to achieve full heating capacity.  However, there may be other space and installation considerations that still justify this type of installation.  In high heat applications, a very high efficiency boiler only achieves efficiencies in the high 80th percentile range.    Systems with cast iron registers or fin tube, baseboard heat usually require 180 degree water. On the other hand, if a home has radiant heat (in-floor tubing), heating costs can be lowered by installing a very high efficiency boiler.  Radiant heat usually needs 120 degree water and takes full advantage of the very high efficiency boiler’s attributes.

Condensing or Non-Condensing Boilers.
Very high efficiency boilers that are designed to run at lower water temperatures are called condensing boilers.  The exhaust air stream is cooled during the process of pulling heat into the boiler water to a temperature low enough to cause condensation to form inside the boiler.   The boiler is designed to drain this condensation away.  Most of these boilers qualify for Focus on Energy rebates and/or Federal Tax Credits.
 
80% to 85% efficient boilers are called non-condensing boilers and require the water temperature in the boiler to stay above 160 degrees so condensation won’t occur (which can shorten the life expectancy of a non-condensing boiler.  We can design “boiler protection” for a system so the boiler is protected against damage from condensation.)  These boilers are generally less expensive to install than very high efficiency boilers.

Boiler Heat Exchanger Types
Most non-condensing boiler heat exchangers are made of cast iron.  The best cast iron boilers have flexible cast iron heat exchangers with a high tolerance for water temperature changes.   Cast iron heat exchangers are customarily thicker in design and weigh more than other heat exchanger types.  As a result, these types of boilers are usually heavier.

Stainless steel heat exchangers are normally used in high efficiency, condensing boilers.  They are small, have thin walls, and are lightweight.  They heat up very quickly and do a good job of transferring heat rapidly from flame to water.  Most stainless steel heat exchanger boilers are around 92% efficient.  Small sizes can be mounted on a wall, while sizes greater than 80,000 BTU’s are usually floor standing.

An aluminum heat exchanger is the newest and most expensive type.  They are used only in very high efficiency boilers and are available in efficiencies as high as 99%.  These boilers are lightweight and usually wall mounted.
 
Gas Valve Types
Most non-condensing boilers have single stage gas valves.  Some have two-stage gas valves which operate very similarly to two- stage furnaces (please see above).
Most very high efficiency boilers have modulating gas valves that vary the output of the boiler based on the current heating demand.  These valves, and their related boiler components, are more expensive than ‘standard’ parts.

Other Boiler System Options
Outdoor Reset saves money by reducing the water temperature based on outdoor temperature.
Zoning allows individual temperature controls in different areas of your home by using zoning valves or separate circulator pumps for each zone on the system

Indirect Domestic Hot Water – This water heater uses a boiler’s heat to make hot water for the home.  These systems typically have 3- 4 times the performance characteristics of a gas fired hot water heater and run more efficiently.  (Gas fired hot water heaters are normally around 60% efficient.)
Grade of Air Elimination System –Automatically removes air from the boiler system to allow for quiet, smooth operation.  These systems vary significantly in quality and performance capabilities.

Type and Size of Expansion Tank – There are different grades and sizes of expansion tanks, which allow for expansion of water in the boiler system as the water is heated.  These should be sized to the volume of water in the boiler system as well as the maximum water temperature the boiler will run at.  They also need to be properly installed so they last.

Air Conditioning