8.4   Heating System Replacement

This section discusses replacing combustion furnaces and boil­ers. We’ll also discuss gas heating-replacement and oil-heating-replacement specifications.

See “HVAC-System Commissioning” on page 252. See “HVAC-System Education” on page 253.

8.4.1   Furnace or Heat Pump Replacement

This section discusses air handlers of combustion furnaces and also heat pumps. Successful air-handler replacement requires selecting the right heating (and cooling) input, blower model, and blower speed. The installation must include making repairs to ducts and other remaining components, and testing to verify that the new air handler operates correctly.

Preparation for Replacement

✓     Recover refrigerant in the existing heating-cooling unit according to EPA regulations.

✓     Disconnect and remove the furnace or heat pump, attached air-conditioning equipment, and other materials that won’t be reused.

✓     Transport these materials off the customer’s property to a recycling facility.

✓     Verify that all accessible ducts were sealed as part of the furnace’s installation, including the air handler, the ple­nums, and the branch ducts.

Equipment Selection

✓     Evaluate the building to determine the correct size of the furnace or heat pump, using ACCA Manual J or equivalent method. Select the smallest BTUH output furnace that exceeds your heat loss calculation and that your preferred manufacturer offers.

✓     Select the air handler using ACCA Manual S or equivalent method along with manufacturers’ air-handler specifica­tions. Consider blower airflow requirements for air condi­tioning (in addition to heating) if the new unit includes central air conditioning.

✓     Select the supply and return registers using ACCA Manual T or equivalent method.

Air-Handler Installation

✓     Install MERV 6 or higher filter inside or outside of the new air handler.

✓     The filter must be easy to replace.

✓     The filter retainer must hold the filter firmly in place.

✓     The filter must provide complete coverage of blower intake or return grille. The filter housing and restraint must not permit air to bypass the filter.

✓     If flue-gas temperature or supply air temperature are unusually high, check static pressure, fuel input, or electri­cal input. See “Ducted Air Distribution” on page 321.

✓     Attach the manufacturer’s literature, including operating manual and service manual, to the furnace or heat pump.

Supporting Air Handlers

Support the new air handlers using these specifications.

•       Support horizontal air handlers from below with a non-combustible, water-proof, and non-wicking material. Or support the horizontal air handler with angle iron and threaded rod from above.

•       Support upflow air handlers with corner support legs, bricks, or pads from below when necessary to hold it above a damp basement floor.

•       Support downflow air handlers with a strong, airtight sup­ply plenum. Insulate this supply plenum to minimize energy loss.

8.4.2   Gas-Fired Heating Installation

The goals of gas-appliance replacement are to save energy and improve heating safety. The heating replacement project should produce a gas-fired heating system in virtually new condition, even though existing components like the gas lines, chimney, pipes, or wiring may remain.

Include maintenance, repair, or replacement of existing compo­nents as part of the installation. Analyze design defects in the original system, and correct the defects during the heating sys­tem’s replacement.

•       If possible, install a condensing sealed-combustion (direct vent) furnace or boiler with a 90+ AFUE.

•       Install new gas-fired unit with adequate clearances to allow maintenance.

•       Follow manufacturer’s venting instructions along with the National Fuel Gas Code (NFPA 54) to install a proper vent­ing system. See “Inspecting Venting Systems” on page 306.

•       Check clearances of the heating unit and its vent connector to nearby combustibles, according to NFPA 54. See page 309. 

•       Measure the new unit’s gas input, and adjust the gas input if necessary.

Testing New Gas-Fired Heating Systems

✓     Do a combustion test, and adjust fuel-air mixture to mini­mize O₂. However don’t allow CO beyond 200 ppm as measured or 400 ppm air-free with this adjustment. See pages 256 and 291. 

✓     Verify that the gas water heater vents properly after instal­lation of a sealed-combustion or horizontally vented fur­nace or boiler. Install a chimney liner if necessary to provide right-sized venting for the water heater.

8.4.3   Combustion Boiler Replacement

Technicians replace boilers as an energy-conservation measure or for health and safety reasons.

Boiler piping and controls present many options for zoning, boiler staging, and energy-saving features. Dividing homes into zones, with separate thermostats, can significantly improve energy efficiency compared to operating a single zone.

Follow these specifications when recommending a replacement boiler.

Design

A boiler’s seasonal efficiency is more sensitive to correct sizing compared to a furnace.

✓     Determine the correct size of the boiler, using ACCA Manual J and considering the installed radiation surface connected to the boiler.

✓     Consider weatherization work that reduced the heating load serviced by the previous boiler when sizing the new boiler.

✓     Size new radiators according to room heat loss and design water temperature.

✓     Specify radiator temperature controls (RTCs) for areas with a history of overheating.

✓     A functioning pressure-relief valve, expansion tank, air-excluding device, back-flow preventer, and an automatic fill valve must be part of the new hydronic system.

Pump and Piping

✓     Verify that all supply piping is insulated with foam or fiberglass pipe insulation.

✓     Suggest that the pump be installed near the downstream side of the expansion tank to prevent the suction side of the pump from depressurizing the piping, which can pull air into the piping system.

✓     Replace the expansion tank, unless it’s the correct size for the new system. Adjust the expansion tank for the correct pressure during boiler installation. See page 359. 

✓     Extend new piping and radiators to conditioned areas, like additions and finished basements, which are currently heated by space heaters.

Controls

✓     Maintaining a low-limit boiler-water temperature is waste­ful. Boiler controls should cold-start the boiler, unless the boiler is used for domestic water heating.

✓     For large boilers, install reset controllers that adjust supply water temperature according to outdoor temperature and prevent the boiler from firing when the outdoor tempera­ture is a sufficient temperature so that heat isn’t needed.

✓     Verify that return-water temperature is above 130° F for gas and above 150° F for oil, to prevent acidic condensa­tion within the boiler, unless the boiler is designed for condensation. Install piping bypasses, mixing valves, pri­mary-secondary piping, or other strategies, as necessary, to prevent condensation within a non-condensing boiler.

Combustion Testing

✓     Inspect the chimney and upgrade it if necessary.

✓     Verify that flue-gas oxygen and temperature are within the ranges specified in these two tables.

a.  “Combustion Standards for Gas Furnaces and Boilers” on page 275

b.  “Minimum Oil Burner Combustion Standards” on page 297

Steam Boilers

Steam-boiler performance depends heavily on the adequacy of the existing steam distribution system. The boiler installer should know how the distribution system performed when it was connected to the old boiler.

The new boiler’s water line should be at the same height as the old boiler’s water line, or the installers should know how to compensate for the difference in water-line levels. See "Steam Heating and Distribution" on page 362.

8.4.4   Oil-Fired Heating Installation

Oil-heating replacement should provide an oil-fired heating sys­tem in virtually new condition, even though components like the oil tank, chimney, piping, and wiring may remain in place.

Any maintenance, repair, or replacement for these remaining components should be part of the replacement job. Analyze design defects of the original system, and correct them during the heating-system replacement.

✓     New oil-fired furnaces and boilers should have a mini­mum AFUE of 83%.

✓     Install new oil-fired furnaces and boilers with adequate clearances to facilitate maintenance.

✓     Inspect the existing chimney and the vent connector. Re-place the vent connector with Type L double-wall vent pipe if necessary.

✓     Install a stainless steel chimney liner if necessary.

✓     Verify that the clearances between the vent connector and nearby combustibles are adequate. See “Clearances to Combustibles for Vent Connectors” on page 309.

✓     Install a new fuel filter, and purge the fuel lines as part of the new installation.

Oil Combustion Controls

✓     Verify that the presence of a functioning emergency shut-off for emergencies and service work. Inform customers of its function for emergencies only.

✓     Look for a control that interrupts power to the burner in the event of a fire.

✓     Measure the transformer voltage to verify that it complies with the manufacturer’s specifications.

✓     Measure the control circuit amperage, and adjust the ther­mostat’s heat anticipator to match the amperage. Or, follow the thermostat manufacturer’s instructions for adjusting cycle length.

Testing New Oil-Fired Heating Systems

✓     Verify that the oil pressure matches the manufacturer’s specifications, but isn’t less than 100 psi.

✓     If the flue-gas temperature is too high, adjust oil pressure per manufacturers instructions or replace nozzle as neces­sary to produce the correct oil input (gpm) and flue-gas temperature.

✓     Verify that the spray angle and spray pattern fit the size and shape of the combustion chamber.

✓     Adjust oxygen, flue-gas temperature, and smoke number to comply with manufacturer’s specifications or the speci­fications given here. Smoke number should be zero on all modern oil-fired equipment.

8.4.5   Evaluating Oil Tanks

Inspect the oil tank, and remove dirt and moisture at bottom of the tank. Verify that the oil tank and oil lines comply with NFPA 31.

Oil tanks are now almost always installed above ground. But many old oil tanks are still buried. Inspect above-ground tanks to find leaks.

Testing can evaluate both below-ground tanks and above-ground tanks for water in the fuel system.

1.      Start by inspecting the oil filter for corrosion. Corrosion in the oil filter indicates a high probability of water and corrosion in the tank.

2.      Next use water-finding paste, applied to the end of a probe, to detect water at the bottom of the oil tank. For indoor tanks, you’ll need a flexible probe because of the ceiling-height limitations.

See also NFPA 31 Chapter 7 Fuel Oil Tanks.

Inspecting Above-Ground Oil Tanks

Indoor oil leaks are usually accompanied by strong petroleum smells. Inspect the oil tank as well as all the oil piping between the oil tank and the oil-fired furnace.

✓     Look for different colors on the tank from condensation, corrosion, or fuel leaks.

✓     Look at the bottom of the oil tank and see if oil is dripping from a leak.

✓     Look for patches from previous leaks.

✓     If the oil tank is new, don’t mistake previous oil-tank leaks for leaks in the new tank.

✓     Use the water test described previously.

If you smell oil but you can’t see the leak, consider the following tests.

✓     Use the water test described previously.

✓     For hidden leaks, consider ultrasound leak detection by a oil-tank specialist.

✓     Advise the residents about the environmental and respira­tory hazards associated with indoor oil tanks.

Advice for Below-Ground Oil Tanks

Leaky below-ground oil tanks are a financial problem and a major environmental problem. Local, state, or federal authori­ties may require homeowners to remove the tank, abandon it in place, or have it leak-tested by one of the following methods.

✓     Use the water testing described previously.

✓     A tank specialist collects multiple soil samples from around the tank and analyzes them for petroleum contam­ination by an approved method.

✓     Advise the residents about the environmental and respira­tory hazards associated with leaking underground oil tanks.