How to Design for Efficient HVAC, Plumbing, and Electrical Layouts

If you’ve ever walked through a finished home and thought, “This place just feels right,” there’s a good chance the HVAC, plumbing, and electrical design quietly did its job. When these systems are designed well, the house is comfortable, the utility bills make sense, hot water shows up fast, lights don’t flicker, and you don’t hear fans roaring like a jet engine. When they’re not, you live with drafts, cold showers, breaker trips, and repair calls. I’ve been on both sides. The difference is almost always decided on paper—long before a single wall is framed.

The Big Picture: Why MEP Design Should Start Early

MEP stands for mechanical, electrical, and plumbing. Treat these as a single coordinated system rather than three separate trades that show up and “make it fit.” You’ll get:

• Fewer surprises: Clear chases for ducts and pipes prevent costly framing changes.
• Better comfort: Accurate HVAC sizing and distribution keeps rooms steady and quiet.
• Lower operating costs: Shorter runs, better insulation, and efficient equipment pay you back.
• Faster hot water: Smart water routing and equipment placement cut wait times.
• Safer, more flexible power: Proper circuit planning, panel capacity, and future-proofing means fewer limitations later.

I like to gather the architect, builder, HVAC/plumbing/electrical contractors, and the HERS rater (or energy consultant) before schematic design is locked. A one-hour coordination meeting at this phase can save thousands later.

Project Workflow That Works

A practical sequence I use on custom homes and major remodels:

1. Set priorities with the owner – Comfort goals (temperature, noise) – Energy targets (code-minimum, ENERGY STAR, net-zero ready) – Preferences (gas vs. all-electric; ducted vs. ductless) – Special loads (sauna, workshop, EVs, hot tub, server closet)

1. Create a utility core strategy – Stack bathrooms and laundry rooms – Reserve chases for ducts and risers – Plan mechanical rooms with real clearance, not leftover corners

1. Do the loads and counts – HVAC Manual J (room-by-room loads), Manual S (equipment), Manual D (ducts) – Plumbing fixture units and pipe sizing – Electrical load calc (NEC Article 220), panel sizing, and circuit map

1. Draft a composite MEP plan – One set of color-coded plans showing ducts, pipes, and wiring paths – Check for conflicts with structure and windows/doors early

1. Review for serviceability – Access to equipment, valves, filters, cleanouts, junction boxes – Pull-down ladders or full doors for attic equipment – Labels, shutoffs, and drain pans

1. Final coordination and sign-offs – Builder sequencing plan (who goes when) – Materials and model numbers approved – Commissioning checklist agreed (more on that later)

Shared Design Principles Across HVAC, Plumbing, and Electrical

• Keep runs short and straight. Every turn adds pressure drop, friction, and complexity.
• Put the big gear central. Air handlers, water heaters, and panels do best in accessible, central locations.
• Get utilities inside conditioned space when possible. Ducts and water lines in the attic or exterior walls work harder and waste energy.
• Stack and align. Bathrooms over bathrooms, kitchen near mechanicals, laundry near water heater.
• Plan real chases. A 14-inch-deep soffit with no framing obstacles beats finding out a 12-inch trunk won’t fit after drywall.
• Leave space for service. An extra foot of access around equipment is cheap on paper and priceless during maintenance.
• Pre-plan penetrations. Coordinate joist and stud holes with structure limits and mark them on the plan.
• Think future. Conduit runs, spare circuits, oversize chases, and labeled valves give you options.

Mechanical (HVAC): Comfort Starts With Numbers

Load Calculations: No Guessing

If you only take one thing from this article: size HVAC by calculation, not rules of thumb. I’ve seen “1 ton per 500 square feet” oversize a tight home by 2x or more. That leads to short cycling, uneven rooms, and humidity problems.

• Use ACCA Manual J (or an approved software like Wrightsoft, CoolCalc, or Elite).
• Input matters: actual insulation values, window U-factor/SHGC, air sealing targets, and orientation.
• Target infiltration based on blower-door goals. Many new homes aim for 3 ACH50 or better; use that in your Manual J.

Typical results for a well-insulated 2,400 sq. ft. home, Climate Zone 4A:

• Heating load: ~24,000–36,000 BTU/h (depends on envelope and windows)
• Cooling load: ~18,000–30,000 BTU/h
• Zoning: 2 zones is common (sleeping vs living). More than 3 zones on a single air handler can get tricky.

Equipment Selection (Manual S): Match The Load

• Heat pumps are now viable in colder climates with variable-speed compressors; look for cold-climate models (e.g., 80–100% capacity at 5°F).
• If using a gas furnace, consider a 2-stage or modulating unit for comfort and noise.
• Choose equipment that meets the load at design conditions, not just “nameplate tons.”
• Efficiency ratings:
• Cooling: SEER2 (look for 15–18 SEER2 as a sensible balance; higher if budget allows)
• Heating: HSPF2 8–9+ for heat pumps
• Furnace: 95%+ AFUE

Cost ballpark (installed, U.S. ranges):

• Central ducted heat pump system: $12,000–$22,000 depending on size, brand, and duct complexity.
• Ductless multi-split: $8,000–$18,000 depending on zones.
• ERV/HRV: $2,000–$5,000 including ducting.

Duct Design (Manual D): Quiet and Balanced

• Keep static pressure low. Most residential systems target total external static under ~0.5 in. w.c. Quiet systems often land 0.3–0.4.
• Velocity targets:
• Main trunks: 700–900 fpm
• Branch runs: 500–700 fpm
• Duct location: Inside conditioned space whenever possible (dropped ceilings, chases along central hallways). If ducts must be in the attic, bury them in insulation and seal meticulously.
• Duct materials: Rigid metal or rigid fiberglass ductboard for mains; short, taut flex for final connections. Long flex runs kill airflow.
• Returns: Provide low-resistance return paths from every closed-door room (jumper ducts or transfer grilles) or dedicated returns in main rooms.
• Control and balancing:
• Manual balancing dampers on each branch
• Supply registers sized to throw air across the room without drafts
• Avoid wall cavities as returns; use lined, dedicated return ducts for cleanliness and noise control

What I look for in plans:

• Maximum 2–3 elbows from plenum to register
• No panned joist returns
• A real return path for each bedroom
• Supply to exterior wall/windows in cooling climates; in cold climates you can supply from interior walls with proper throw and mixing

Ventilation and IAQ: The Unsung Hero

• Follow ASHRAE 62.2 for ventilation rate. Rough guide: 0.03 × floor area (sq. ft.) + 7.5 × (bedrooms + 1). A 3-bed, 2,400 sq. ft. home needs roughly 90 CFM continuous.
• Balanced ERV/HRV provides fresh air efficiently. Duct it separately or tie into the return side of the air handler with proper controls.
• Filtration: Aim for MERV 13 filters if your blower can handle it without excessive static. Check pressure drop specs.
• Kitchen ventilation: Use a ducted range hood (not recirculating) with at least 150–300 CFM for standard cooking. If the hood exceeds 400 CFM, many codes require makeup air (IRC M1503). Plan this early—it’s a common gotcha.
• Bathroom fans: 50 CFM intermittent or 20 CFM continuous per bath. Choose quiet models (≤1.0 sone; I prefer 0.3–0.7). Duct to exterior with smooth duct, short runs, and sealed connections.

Condensate and Defrost Management

• Air handlers and coils need proper drain pans with float switches.
• Secondary drain pan under attic air handlers with a drain or a wet-switch overflow sensor.
• Heat pumps in cold climates: plan condensate and defrost water routing so you don’t ice over a walk path.

Noise Control

• Put air handlers on vibration isolation pads.
• Avoid placing air handlers or ducts directly over bedrooms if possible.
• Keep outdoor units away from bedroom windows and neighbors’ patios. Many municipal noise ordinances set limits near property lines.

Commissioning Checklist

Before final payment, I like to see:

• Measured supply airflow at each register and total airflow vs design CFM
• Static pressure readings (supply/return) within manufacturer limits
• Refrigerant charge verified via superheat/subcool per outdoor conditions
• Balanced ventilation rates (ERV/HRV) verified with a flow hood or anemometer
• Thermostat programming explained to owner
• Filter sizes, locations, and maintenance schedule documented

HVAC Case Example: 2,400 sq. ft. Two-Story, Mixed Climate

• Load calc yields 2.5 tons cooling, 28k BTU heating.
• Equipment: 3-ton variable-speed heat pump selected to cover load and give modulation.
• Ducts: Central upstairs mechanical closet; trunks run in hallway soffits; all ducts inside conditioned space.
• Returns: One per bedroom wing and a central main return; jump ducts for bedrooms.
• Ventilation: 100 CFM ERV, tied to return with motorized damper and controller. Boost via bath fan switches.
• Range hood: 300 CFM, backdraft damper, no makeup air needed by code; house tightness verified to avoid depressurization issues.
• Results: Quiet operation, even temperatures, blower door 2.5 ACH50, happy owners.

Plumbing: Hot Water Fast, Drains That Don’t Gurgle, Pipes That Last

Water Supply: Sizing and Strategy

• Pressure and quality: Test incoming static pressure. If over 80 psi, install a pressure-reducing valve (PRV) and a thermal expansion tank for closed systems. Hard water? Budget for softening or conditioning, especially with tankless units.
• Pipe sizing: Use fixture units (IPC or UPC tables) to size mains and branches. A typical single-family might use:
• 1” service from the street
• 3/4” trunk line to manifolds or major branches
• 1/2” to individual fixtures (sometimes 3/8” for short runs to lav faucets)
• Layout options:
• Trunk and branch: Simple, fewer parts; can have pressure fluctuations with multiple simultaneous users.
• Home-run manifold (PEX): Individual 1/2” runs from a central manifold; consistent pressure; easy isolation; can reduce water waste if centrally located.
• Hybrid: A small trunk with manifolds serving room groups.

Pro tip from the field: If your house is long or has distant baths, a central mechanical closet cut average hot water wait times by half compared to a garage water heater.

Hot Water Systems

• Storage tank (gas or electric): Reliable, lower upfront cost. Keep the heater inside conditioned space or a well-insulated mechanical room when possible.
• Heat pump water heater: Very efficient, dehumidifies the space; needs adequate room volume and a drain. Great in warm climates or basements.
• Tankless: Endless hot water but sensitive to flow and water hardness; maintenance matters. Install service valves for descaling.
• Recirculation:
• Dedicated recirc return line with ECM pump and smart control (schedule, aquastat, or demand button) saves both time and water.
• Gravity recirc can work on some layouts but is rare in newer tight homes.
• Temperature: Set water heater to 120°F at the tap. If you need higher storage temps for Legionella mitigation, use a mixing valve.

Typical costs (installed):

• Standard tank water heater: $1,500–$3,500
• Heat pump water heater: $2,500–$5,500 (rebates often available)
• Tankless: $3,000–$6,500
• Recirculation loop with pump: $500–$1,500

Drain, Waste, and Vent (DWV)

• Slopes: 1/4” per foot for 2-1/2” and smaller; 1/8” per foot for larger lines (per code). Too steep and water outruns solids; too flat and clogs form.
• Wet venting: Allowed in many jurisdictions under strict layout rules. Coordinate fixture grouping early.
• Cleanouts: At the base of stacks, major direction changes, and within required distances per code.
• Vents:
• Regular vent stacks sized per aggregate fixture units
• Air admittance valves (AAVs) only where allowed; use quality valves and accessible locations
• Penetrations: Group roof penetrations where possible; flash correctly
• Noise: Use isolation clamps, avoid strapping pipes hard to studs, and consider cast iron for vertical stacks adjacent to bedrooms for sound.

Leak Protection and Serviceability

• Full-bore ball valves on main and branch lines; label them.
• Smart leak detectors with auto-shutoff (under water heater, at washer, and in mechanical room).
• Drain pans under water heaters and washers with drains where possible.
• Access panels for key traps, valve sets, and AAVs.

Irrigation, Hose Bibs, and Backflow

• Irrigation requires backflow prevention—RPZ valves where required; ensure drainage for test ports.
• Anti-siphon hose bibs; insulate and use frost-free types in cold climates.
• Run hose bibs on a dedicated cold line to avoid warm water outdoors in summer if near recirc loops.

Real-World Plumbing Setup: Two-Story, Three-Bath

• Wet wall stack aligned through both floors, mechanical closet beneath.
• 3/4” cold trunk feeds manifolds; 3/4” hot trunk from water heater to second-floor manifold.
• Dedicated 1/2” hot recirc line looping main bathrooms back to heater with demand-control pump.
• DWV: Common vent between back-to-back vanities; dedicated vent for kitchen sink due to island (use AAV or island vent loop depending on code).
• Leak management: Pan and sensor under water heater; auto-shutoff valve; washer pan with drain to garage.

Common Plumbing Mistakes I See

• Water heater in the farthest corner of the garage with 80 feet to the owner’s shower. Result: 90+ seconds for hot water.
• No PRV on high-pressure city water; constant drip at T&P valve and shortened fixture life.
• Overuse of AAVs with no access panel.
• No isolation valves at fixtures; repairs become full-house shutoffs.
• Support spacing ignored; PEX droops, traps air, and looks sloppy.

Electrical: Power, Lighting, and Controls That Feel Effortless

Service and Panel Sizing

• Do a proper load calc (NEC Article 220). Many new homes of 2,000–3,500 sq. ft. with electric cooking, HVAC, and EV charging do well with 200A service. All-electric homes with multiple heat pumps and EVs may need 300A or a careful load management strategy.
• Plan for future loads:
• 60A for EV charger(s) (often 40–50A continuous load)
• 30–60A for future hot tub or sauna
• Conduit to roof for PV
• Subpanels can simplify wiring and future changes, especially in detached garages or large homes.

Estimated costs:

• 200A panel upgrade: $1,800–$3,500
• EV charger install: $800–$2,000 depending on run distance and panel capacity
• Whole-home surge protector: $250–$700 installed

Circuit Planning: Dedicated Where It Matters

• Kitchen:
• Two 20A small-appliance circuits for countertop receptacles (GFCI/AFCI protection)
• Dedicated circuits for microwave, dishwasher and disposal (often shared with handle-tied double-pole breaker if required by manufacturer), refrigerator, and range/oven
• Laundry: Dedicated 20A for washer; 30A/240V for electric dryer (or gas with 15/20A outlet)
• Bathrooms: 20A GFCI circuit(s); a single 20A can serve multiple baths for receptacles if wired correctly, but I prefer one per bath in larger homes
• HVAC: Dedicated circuits for air handler, condenser/heat pump, ERV/HRV, and electric heat strips if present
• Lighting: Separate from receptacle circuits for troubleshooting and safety
• Exterior: GFCI-protected, in-use covers, front and back
• Specialty: Sump pump, radon fan, server rack, workshop tools—dedicated circuits keep nuisance trips down

AFCI and GFCI:

• AFCI required in most habitable rooms (NEC 210.12).
• GFCI required for kitchens, baths, laundry, garages, unfinished basements, outdoors, and within 6 ft of sinks (NEC 210.8). Many jurisdictions now require GFCI for refrigerators; if so, use a dedicated GFCI-protected circuit to reduce nuisance trips.

Receptacle Spacing and Locations

• General rule: No point along a wall line more than 6 feet from a receptacle; receptacle within 6 feet of openings like doors (NEC 210.52).
• Kitchen counters: Receptacles so that no point along the countertop is more than 24 inches from one; island and peninsulas require specific solutions (often a pop-up or side-mounted receptacle).
• Hallways over 10 feet: At least one receptacle.
• Bedrooms: Plan outlets for bed wall lamp cords; include a receptacle at each nightstand location.

Pro tip: Add a floor box in living rooms where furniture floats. It avoids extension cords and looks sharp.

Lighting Design That Feels Right

• Use a layered approach:
• Ambient: Recessed cans or ceiling fixtures
• Task: Undercabinet lights, vanity lights, reading lights
• Accent: Wall washers, toe-kicks, toe-kick night lights
• Color temperature: 2700K–3000K in living areas and bedrooms, 3000K–3500K for kitchens and workspaces.
• Output guidelines:
• General living: 10–20 lumens per square foot
• Kitchen task areas: 50+ lumens per square foot at the countertop
• Home office: 50 lumens per square foot on the desktop
• Controls:
• Dimmers on most ambient circuits
• Vacancy sensors in kids’ baths and closets
• Daylight sensors for exterior lights
• Consider a centralized smart lighting system if the budget allows; otherwise, use smart dimmers strategically

Low-Voltage and Networking

• Run CAT6 (or CAT6A for 10Gb future-proofing) to TVs, office desks, access points (ceiling), security cameras, and media cabinets.
• Use a structured media panel or rack; home-run all low-voltage to it.
• Run conduit (1–1.5”) to strategic points (TVs, exterior eaves for cameras, attic for future solar/battery gear). Conduit is cheap; fishing wire later is not.
• Speaker wire: 14/2 or 14/4 CL2/CL3 as needed; plan volume control or centralized amp locations.

Safety, Surge, and Backup Power

• Whole-home surge protection paired with point-of-use surge strips for electronics.
• Smoke/CO detectors: Hard-wired with battery backup and interconnection.
• Backup options:
• Generator with transfer switch or interlock: Size for essentials or whole house.
• Battery backup systems: Pair well with solar; coordinate main panel and subpanel for critical loads.

Workmanship Tips That Pay Off

• Maintain proper cable bend radius. Avoid over-stapling NM-B.
• Drill holes in the third of the stud, maintain required distances from edges, and use nail plates where needed.
• Label everything—panel schedules that match labels on cables in the attic or mechanical room save hours later.
• Keep neutrals and grounds separate in subpanels; bond only at the main service.

Coordinating All Three: Where The Magic Happens

Use a Composite MEP Plan

I color-code each system:

• Blue for cold water
• Red for hot water
• Green for DWV
• Orange for ducts and ventilation
• Yellow for electrical
• Purple for low voltage

Overlay them with structural plans. Look for:

• Duct straps crossing beam flanges (bad)
• 3” drains trying to pass through engineered joist webs without pre-approved knockouts
• Conflicts at the top plate for stacked baths

A 30-minute clash-detection pass in SketchUp, Revit, or even Bluebeam markups easily pays for itself.

Plan Chases and Soffits Like Features, Not Afterthoughts

• A clean 16-inch-wide, floor-to-ceiling chase near the stair can carry a main return, ERV ducts, and plumbing risers. Wrap it as a design element.
• Use dropped ceilings in hallways to keep ducts inside conditioned space and maintain full-height ceilings in main rooms.

Penetrations, Firestopping, and Air Sealing

• Pre-mark joist and stud penetrations per manufacturer limits (especially for I-joists and trusses).
• Firestop with approved materials at every floor and top/bottom plate penetration.
• Seal duct, pipe, and wire penetrations in the air barrier with mastic, gaskets, or foam. A tight home works better and allows smaller HVAC.

Sound Control Between Systems

• Don’t mount return grilles on bedroom walls without acoustic lining in the return path.
• Use resilient mounts for air handlers.
• Isolate plumbing from studs with cushioned clamps. Consider cast iron stacks near high-end bedrooms.

Sequence Matters

• Frame and mark chases → Rough in HVAC mains and returns → Rough in plumbing → Rough in electrical → Low-voltage last
• Keep coordination meetings weekly during rough-in to solve surprises quickly.

Energy, Code, and Performance Targets Worth Hitting

• Air leakage: Aim for ≤3 ACH50 in new construction. Many projects hit 1.5–2.5 with good air-sealing details.
• Duct leakage: If any ducts are outside conditioned space, target ≤4 CFM25 per 100 sq. ft. of conditioned floor area or better; inside the envelope, aim as low as possible (I like ≤3% of fan flow).
• Ventilation rate: Size to ASHRAE 62.2 and verify delivered CFM.
• Range hood makeup air: Provide if hood exceeds 400 CFM (IRC M1503).
• Dryer ducts: Smooth metal, limited length with equivalent fittings accounted for. Avoid tight 90s.
• Electrical: Follow NEC for AFCI/GFCI, receptacle spacing, and load calcs; local amendments can be stricter.
• Plumbing: Follow IPC/UPC; verify venting rules and AAV allowance locally.

Partnering with a HERS rater or energy consultant early helps you align envelope details with HVAC sizing and ventilation.

Budgeting and Timeframes

Planning-level cost ranges for a typical 2,400–3,000 sq. ft. home (U.S. averages, mid-grade materials):

• HVAC: $12,000–$25,000 (add $2,000–$5,000 for ERV/HRV; higher for zoning/variable-speed systems)
• Plumbing: $12,000–$22,000 (more with recirc and water treatment)
• Electrical: $10,000–$20,000 (add for smart controls, EV, generator)
• Low voltage: $1,000–$6,000 (depends on network, audio, and security scope)

Timeframes (rough-in phases):

• HVAC rough-in: 5–10 working days
• Plumbing rough-in: 4–8 working days
• Electrical rough-in: 5–10 working days

These vary with complexity, crew size, and inspection scheduling.

Common Mistakes and How to Avoid Them

• Oversized HVAC. Fix: Do Manual J/S/D; choose modulating equipment; verify infiltration assumptions.
• Ducts in a vented attic. Fix: Bring ducts inside with soffits/chases; or at least bury and seal them.
• Starved returns. Fix: Return paths for all closed-door rooms or dedicated returns.
• Long hot water waits. Fix: Centralize heater; use manifolds; add a demand-controlled recirc.
• No makeup air for big hoods. Fix: Plan powered makeup air with interlock on hoods ≥400 CFM.
• Under-sized electrical panel. Fix: Do a real load calc and plan for EV/PV/battery.
• Too few outlets or poor placement. Fix: Walk the plan with furniture layout and gadgets in mind; add floor boxes.
• No access to valves, filters, and junctions. Fix: Place gear smartly and include access panels.
• Sloppy penetration planning. Fix: Layout holes before drilling, use nail plates, and follow joist manufacturer guidelines.
• Skipping commissioning. Fix: Require airflow, static, ventilation, and control verification.

Step-by-Step: From Blank Plan to Coordinated MEP

1. Owner kickoff – Equipment preferences, allergies/IAQ concerns, cooking style (gas vs induction), long-term plans (EV, solar) – Hot water priority fixtures (owner’s shower, kitchen, laundry)

1. Envelope targets set – Insulation specs and window performance locked in before HVAC sizing – Air-sealing details included (zip, tapes, gaskets)

1. Room-by-room HVAC loads – Compute Manual J with realistic infiltration and internal gains – Decide on zoning and equipment placement (mechanical room identified)

1. Plumbing fixture schedule and counts – Size water service and mains; choose trunk/branch vs manifold – Place water heater and recirc strategy; align wet walls

1. Electrical load calc and circuit map – Determine service size and subpanel needs – Plan dedicated circuits for kitchen, laundry, HVAC, and special equipment

1. Composite MEP plan drawn – Color-coded, with chases and soffits – Verify structural penetrations; coordinate with truss joist specs

1. Product selection – Model numbers for HVAC (air handler, outdoor unit, ERV, thermostats) – Water heater type and size; fixture flow rates; valve brands – Panel brand, breaker types, lighting controls, low-voltage hardware

1. Pre-rough coordination meeting – Builder sets sequencing and inspection schedule – Confirm access panels and ceiling drops

1. Rough-in with weekly check-ins – Trades walk together at 25% and 75% rough-in to catch conflicts – Take photos for records before drywall

1. Testing and commissioning – Blower door, duct leakage, ventilation balance, HVAC airflow and static – Plumbing pressure tests, temperature settings, leak detection tests – Electrical AFCI/GFCI test, labeling, torque log on lugs, SPD verification

1. Owner orientation – Show filters, valves, breakers, recirc controls, and maintenance intervals – Provide a one-page quick reference and a digital binder with manuals

Real Projects: What Worked and What Didn’t

Case 1: 1950s Ranch Remodel With Tight Chases

The house had low attic clearance and a maze of framing. The owner wanted quiet, efficient cooling and heating, but ducts wouldn’t fit without ugly soffits.

• Solution: Two-zone ductless mini-split system with one slim-duct unit serving bedrooms via short, insulated runs in a dropped hallway ceiling, and a wall cassette in the living area. Electric panel upgraded to 200A.
• Plumbing: Replaced galvanized with PEX manifold; water heater relocated from garage corner to interior closet to shorten runs.
• Electrical: Added dedicated 20A circuits for kitchen appliances and GFCI/AFCI where required; upgraded lighting with warm LED downlights and undercabinet strips.
• Result: No bulky soffits, quiet operation, hot water wait times reduced from ~75 seconds to ~20–30 seconds at most fixtures.

Lesson learned: In remodels, slim-duct mini-splits and manifold plumbing give you flexibility without carving up the house.

Case 2: 3,200 sq. ft. New Build, Energy-Focused Owner

Goals were low energy bills, great IAQ, and future-ready power.

• Envelope: Tight air-sealing strategy; blower door at 1.8 ACH50.
• HVAC: 3-zone variable-speed heat pump with ducts entirely inside conditioned space. MERV 13 filtration. 120 CFM ERV balanced to 0.0–0.1 in w.c. house pressure.
• Plumbing: Heat pump water heater in insulated mechanical room with condensate drain; dedicated recirc loop on a demand button; softener and sediment filter due to well water.
• Electrical: 200A main with a 125A garage subpanel, two 60A EV-ready circuits, whole-home surge protection, structured media panel with CAT6A to all key rooms and ceiling WAPs. Conduit to roof for future PV and battery.
• Controls: Simple smart thermostats; vacancy sensors in closets; dimmers throughout.
• Result: Owners report even temperatures, low bills, and fast hot water. When they added an EV a year later, the infrastructure was waiting.

Lesson learned: A central mechanical room and a composite MEP plan made the build cleaner and faster. Conduit and subpanels made future changes painless.

Practical Room-by-Room Tips

• Kitchen
• Ducted range hood sized to the cooktop; short, smooth duct to outside
• Two or more circuits for countertop receptacles; undercabinet lighting on separate dimmer
• Consider a pot filler on a recirc loop if the cook is serious; include a shutoff

• Owner’s suite
• Ensure return air path if the door is closed
• Place supply register to avoid blowing directly on the bed
• Add floor box near seating area for lamps

• Laundry
• Pan under washer with drain; 20A dedicated circuit; consider a 120V heat pump dryer to avoid long vent runs
• Hot/cold shutoffs easily accessible; leak detector with auto shutoff is cheap insurance

• Mechanical room
• Lighting bright enough to work by (think 50 lumens per sq. ft.)
• Clearances per manufacturer plus a comfort margin
• Floor drain if possible; wall space for expansion tank, filter sets, and manifolds

• Garage
• Subpanel and EV conduit pre-run
• Exterior GFCI outlets on each side for yard tools
• Weather-resistant fixtures and in-use covers

• Attic and crawlspaces
• Avoid equipment here if possible; if not, provide safe access, lights, and decked service platforms
• Insulate pipes and seal all penetrations meticulously

Details That Save Headaches

• Range hood and airtight homes: A 600 CFM hood can backdraft a water heater. Interlock makeup air or choose a right-sized hood. Test with all exhausts running.
• Thermostat location: Avoid exterior walls, direct sun, and supply registers. Central interior walls at about 60 inches height work well.
• Return grille placement: Keep away from kitchen and baths to avoid odors and grease.
• Recirc controls: Demand buttons near the kitchen and owner’s bath let you get hot water when needed without wasted energy.
• Labeling: Put a laminated legend in the mechanical room showing which valve or breaker serves what. Your future self will thank you.

Choosing Trades and Holding Standards

• Ask for ACCA Manuals J/S/D reports in your bid package, not just “a 3-ton will do.”
• Request product submittals with static pressure data, filter sizes, and coil pressure drops.
• Have plumbers provide a schematic with pipe sizes and valve locations.
• Electricians should provide a circuit schedule and panel layout up front.
• Include commissioning tasks in contracts with sign-off sheets.

I’ve seen bids drop once contractors realize the design is clear and coordinated. People price confusion with a healthy margin.

Commissioning and Owner Handoff: The Last 5% That Drives 50% of Satisfaction

• Blower door report with target met
• Duct leakage test results
• HVAC:
• Static pressure and airflow data sheet
• Refrigerant charge confirmation
• Thermostat programming guide
• Ventilation:
• Measured CFM by device and mode
• Filter model and change interval
• Plumbing:
• Pressure test record
• Water heater setup (temp, mode, timer)
• Recirc controls and demo
• Leak detector test
• Electrical:
• Panel schedules finalized
• SPD status lights checked
• AFCI/GFCI test buttons demonstrated
• Digital binder with manuals, serial numbers, and warranty info

When owners know how to use and maintain the systems, performance stays high and callbacks drop.

Quick Reference Checklists

HVAC Pre-Construction

• Manual J loads completed and reviewed
• Equipment selected per Manual S; static calculations considered
• Ducts inside conditioned space where possible; Manual D complete
• Returns planned for all rooms or transfer paths in place
• ERV/HRV sized and ducted with access for filter changes
• Range hood and makeup air coordinated
• Condensate management and drain pans shown on plan

Plumbing Pre-Construction

• Water service size and PRV/expansion tank planned
• Water heater location central; recirc strategy decided
• Manifold vs trunk/branch chosen and drawn
• DWV slope, cleanouts, and vents coordinated
• Leak detectors and shutoff valves specified
• Hose bibs and irrigation backflow planned

Electrical Pre-Construction

• Load calc complete; panel and subpanels sized
• Circuit map with dedicated circuits identified
• Receptacle spacing per code and furniture plan
• Lighting layers, color temps, and controls specified
• Low-voltage runs and conduit for future upgrades shown
• Whole-home surge protector added

Final Thoughts From the Job Site

The best MEP designs are almost invisible to the people living in the home. They feel the outcome—quiet rooms, steady temperatures, light exactly where they need it, water hot when they want it—not the engineering behind it. Getting there isn’t complicated, but it is deliberate.

When I walk a framed house with trades, tape measure in one hand and colored markers in the other, I’m looking for short runs, smooth curves, real access, and systems that work together. Spend the design time up front, commission the systems at the end, and you’ll deliver a home that simply works—day one and ten years later.