Answers

Answers

• What wire size do I need for a 50-amp circuit?
• Does NEC require 75°C or 90°C ampacity?
• How do I derate wire for high ambient temperature?
• What size wire do I need for a 50 amp hot tub?
• Is romex inside conduit derated?
• Do I have to upsize wire for a long run?
• Does a VFD or EV charger count as a continuous load?
• How many wires can I put in conduit before I have to derate?
• What size gas line do I need for a 199,000 BTU tankless water heater?
• Can I use CSST for natural gas?
• What pressure drop does NFPA 54 allow?
• Where is the 2 psi natural gas pipe sizing calculator?
• How do I size a 2 psi natural gas line?
• Gas pipe capacity chart for 2 psi systems
• How many BTU do I need to heat a 2000 sq ft house?
• Is bigger always better for furnace sizing?
• How does climate zone affect heating load?
• What is the maximum voltage drop NEC allows?
• How do I calculate voltage drop for a long run?
• Does voltage drop require upsizing the EGC?
• What NEC article covers allowable voltage drop?
• Voltage drop calculator for branch circuits
• What does AHJ mean in the National Electrical Code?
• Can the AHJ override the NEC, and how do I find mine?
• Does Alaska use the 2020 or 2023 NEC?
• What are Alaska’s state amendments to the NEC for residential work?
• What is normal residential water pressure?
• Why does my pressure drop when multiple fixtures run?
• How much pressure do I lose per foot of elevation?
• Why is my water pressure 90 PSI and is that bad?
• Do I need an expansion tank with a PRV?
• Is 40 PSI too low for a house?
• Why does my PRV whine or vibrate?
• Can I install a PRV myself or do I need a permit?
• What size duct do I need for a 3-ton AC unit?
• Should I use flex duct or sheet metal?
• What is friction rate in duct design?
• What size water heater do I need for a family of 4?
• What size tankless water heater do I need?
• Is first-hour rating or recovery rate more important?
• How many fixture units is a toilet?
• What is the difference between DFU and WSFU?
• How do I convert fixture units to GPM?
• What is the minimum slope for a drain pipe?
• Can a drain have too much slope?
• What slope do I need for a 4-inch sewer line?
• How do I calculate a 1/4 inch per foot slope for a drain pipe?
• What is the total drop for a 1/4 per foot pipe slope over 50 feet?
• Standard pipe slope requirements chart
• What size drain pipe do I need for a bathroom?
• How many fixtures can a 2-inch drain handle?
• Does every plumbing fixture need its own vent?
• How many BTU do I need to cool a 1,000 sq ft house?
• Is it bad to oversize an air conditioner?
• How many square feet does a 2-ton AC cool?
• How many BTUs do I need for my room size?
• AC tonnage and cooling capacity calculator
• Should I round HVAC tonnage up or down?
• Is this calculator a replacement for Manual J or Manual S?
• Why does the calculator stop at 5 tons?
• What should superheat be on a fixed-orifice system?
• What is a good subcooling number?
• Do I charge by superheat or subcooling?
• What is a heat pump balance point?
• At what temperature does a heat pump stop working?
• How do I lower my heat pump balance point?
• At what temperature does a heat pump become inefficient?
• Minimum outdoor operating temperature for a heat pump
• Do heat pumps work below freezing?
• How do I find the balance point of a heat pump?
• What is the thermal balance point temperature formula?
• What is the difference between SEER and SEER2?
• Is a higher SEER2 worth the cost?
• What does HSPF2 measure?
• How do I look up an AHRI reference number?
• What is an AHRI match or AHRI certification?
• How many wires can I put in a 1/2-inch conduit?
• What is the maximum conduit fill percentage?
• Does the ground wire count in conduit fill?
• Does conduit fill include insulation thickness or just copper?
• What if my conduit fill is over 40 percent?
• Does a short conduit nipple really allow 60 percent fill?
• Do spare conductors count toward conduit fill?
• How do I calculate box fill?
• How many wires can I put in a single-gang box?
• Does a receptacle count toward box fill?
• What size drain pipe do I need for the number of fixtures I have?
• What is a drainage fixture unit (DFU)?
• Does this size the vents too?
• How do I size an expansion tank for a closed hydronic heating system?
• Why does the expansion tank depend on temperature?
• Does the expansion tank replace the relief valve?
• How many GPM do I need for a given BTU heating load?
• What pipe size should a hydronic loop be?
• Why keep water velocity under 4 ft/s?
• How do I calculate pump head for a hydronic circulator?
• How are fittings accounted for in pump head?
• What pump velocity is too high in a hydronic loop?
• How do I calculate pump horsepower from GPM and head?
• What does pump efficiency mean here?
• Why round up to the next standard motor size?
• What size water pipe do I need for a given GPM?
• How much water flow can a pipe carry?
• Why does the hot water line option lower the velocity limit?
• What pressure drop should I assume per 100 feet for house water lines?
• How do fittings change my water flow calculation?
• What velocity is too high for copper domestic water?
• Why does fixture flow show lower than pipe capacity?
• What is equivalent length in pipe sizing?
• How do I calculate the cut length for a 45 degree pipe offset?
• What is a rolling offset and how does this handle it?
• Why does joint type change the cut length?
• How much whole-house ventilation does ASHRAE 62.2 require for a 2000 sq ft, 3-bedroom house?
• Does this number include bathroom and kitchen exhaust fans?
• Why does the calculation use bedrooms instead of actual occupants?
• How do I calculate the total cost of a plumbing or HVAC job with markup?
• What is the difference between markup and contingency here?
• Are the indicative material prices accurate enough to quote from?
• How much money will a more efficient appliance save me per year?
• How is the CO2 reduction estimated?
• What electricity rate should I use?
• What size electrical service do I need for a 1,500 sq ft house?
• What is the difference between the standard and optional dwelling load methods?
• How is the neutral load sized for a dwelling service?
• How do I calculate three-phase kW from volts and amps?
• What is the difference between apparent power and true power?
• Can I use this calculator to size motor branch-circuit wire?
• Why does my calculated horsepower not match the motor nameplate?
• Do I enter line-to-line voltage or line-to-neutral voltage?
• Can I estimate generator loading with this?
• How do I size an equipment grounding conductor from breaker size?
• Is EGC size based on load amps or breaker amps?
• Do I have to upsize the ground wire when I upsize phase conductors?
• Can I run aluminum EGC in conduit feeders?
• What if multiple circuits share one raceway?
• Does this tool size grounded neutrals too?
• What size breaker and wire do I need for a 10 hp 460V three-phase motor?
• Why does the motor calculator use table FLC instead of the nameplate amps?
• Can I use this calculator for a VFD or HVAC compressor circuit?
• How far can I run Cat 6 cable?
• What is insertion loss on a network cable?
• Why are only certain frequencies available?
• How far can I run Cat 6 for PoE?
• How much power does a PoE switch need per port?
• Why does 802.3bt deliver more power than 802.3af?
• How do I calculate voltage drop on a 24V thermostat wire?
• Is there an NEC voltage-drop limit for Class 2 circuits?
• My low-voltage run drops too much — what do I do?
• How many Cat 6 cables fit in 1-inch conduit?
• What is the conduit fill limit for low-voltage cable?
• Why are low-voltage cables sized by outer diameter?
• How do I check the refrigerant charge with superheat or subcooling?
• What target superheat should a fixed-orifice system have?
• Do I need a license to charge a refrigerant system?
• Should I charge by superheat or subcooling?
• What does high superheat and low subcooling mean together?
• Why does my target subcool come from the nameplate?
• What if outdoor temperature is very low during charging?
• Does refrigerant blend glide affect this calculation?
• What size line set do I need for a 3-ton AC?
• Why does a freezer need a bigger suction line than an AC of the same tonnage?
• Does line-set length affect the size I should run?
• Can I reuse an existing line set when replacing a condenser?
• When do I need to upsize the liquid line for long runs?
• Why is suction line size tied to evaporator temperature?
• What equivalent length should I use for elbows and fittings?
• How do I calculate the refrigeration load for a walk-in cooler?
• What size refrigeration unit do I need for a walk-in freezer?
• Why is a safety factor added to the walk-in load?
• How many solar panels fit on a 600 sq ft roof?
• How is annual solar production estimated?
• What is the performance factor in solar sizing?
• How many panels can I put on one string for a 1000 V inverter?
• Why does winter temperature reduce max modules per string?
• Why do I also need a minimum module count?
• Can I mix different module models in the same string?
• Should I use design heating temperature or record low for Voc checks?
• Does this replace the inverter manufacturer string tool?
• Why do solar panels produce less than nameplate in summer heat?
• What is NOCT and where do I find it?
• Does roof mounting really make a big performance difference?
• Can wind improve panel output?
• Should I model at 1000 W per square meter all year?
• Is this enough to estimate annual production?
• What is a good DC to AC ratio for residential solar?
• Is clipping always bad in solar design?
• Why would anyone oversize DC above inverter AC rating?
• Can I use the same ratio in low-sun and high-sun markets?
• How does shading affect clipping decisions?
• Do utilities limit DC to AC ratio for interconnection?
• What does LCOE mean for a homeowner solar project?
• How is LCOE different from simple payback?
• What discount rate should I use for residential solar?
• Should incentives reduce capex or be modeled later?
• Can two systems with the same payback have different LCOE?
• Does this include battery replacement costs?
• How long will a 13.5 kWh battery run my house?
• What is usable battery capacity versus nameplate capacity?
• Can rooftop solar recharge batteries during an outage?
• Should I size for whole-home backup or critical loads only?
• Why does motor startup still trip backup systems?
• Is daily cycling hard on backup batteries?
• What is the payback period on a $25,000 solar system?
• How are solar incentives applied to the cost?
• Does the solar payback calculator account for rate inflation?
• How do you calculate sprinkler flow from K-factor?
• Can I use pump pressure instead of sprinkler pressure?
• Is single-head flow enough to size a system?
• How much flow does a K-5.6 sprinkler need at 7 psi?
• Can I back-calculate pressure from required sprinkler GPM?
• Does this include hose allowance or remote area calculations?
• What happens if pressure doubles at the sprinkler?
• What is the Hazen-Williams equation for sprinkler friction loss?
• Which C-factor should I use for fire sprinkler pipe?
• Should fittings be included in the run length?
• What is bend allowance in sheet-metal fabrication?
• What K-factor should I start with?
• Why can finished parts still be off after using bend allowance?
• How is steel pipe weight per foot calculated?
• Does this include fittings and water weight?
• Can I use this for non-steel pipe?
• What is the welding heat-input formula?
• Why does travel speed change heat input so much?
• Can this replace WPS/PQR requirements?
• Can I use CPVC instead of black steel for a residential sprinkler system?
• When do you have to bevel pipe before welding it for fire protection work?
• What is a pre-fabricated pipe spool and why do fab shops build them off-site?
• Do I need a smoke detector or a heat detector in an unconditioned garage?
• What is a NAC and why does my fire alarm panel need a booster for it?
• When does code require VESDA instead of regular smoke detectors?
• What does a jockey pump actually do in a fire-pump system?
• When is a diesel fire pump required instead of an electric one?
• Why does a building need a fire department connection if it already has a city water supply?
• When do you use intumescent coating instead of spray-applied cementitious fireproofing on structural steel?
• How do I pick between firestop sealant, mortar, and wrap strip for a wall penetration?
• When does code require a fire damper vs. a smoke damper vs. a combination damper in ductwork?
• Should fire-protection brackets and apparatus panels be laser-cut or waterjet-cut?
• What does structural welding mean for fire-protection work and which AWS code applies?
• What gets CNC-machined in a fire-fabrication shop and what stays manual?
• How do I choose between FM-200 and Novec 1230 for a clean-agent suppression system?
• When does NFPA 68 require explosion-vent panels instead of a suppression system?
• What's the difference between HSSD and a regular VESDA aspirating system?