Custom home mechanical systems
The room should
feel as good as it looks.
You find the chair with the best view. A moment later, the air comes on and lands on the back of your neck. The room has met its temperature setting, but you move anyway.
That small disappointment is a useful place to begin a conversation about heating and cooling. The equipment is there to serve a person in a room. Its capacity, controls and position all contribute to an experience that a photograph cannot describe.
Start with the chair.
Tell the design team where you expect to sit, sleep and work. A sunroom, a bedroom and a kitchen have different patterns of use, different exposures and different sources of heat. The room schedule should describe those differences before it becomes an equipment schedule.
In a conversation with architect Robert Cardello, Scott Hobbs describes variable-speed air handlers in terms of how the air arrives: a gentler ramp rather than a sudden rush. His account brings the discussion back to the occupant. The historical cost and zone-count examples in that conversation illustrate particular choices, not a required specification for every custom home.1
At Mid Country Grandeur, the sunroom offers a view in several directions. For a room with extensive glazing, ask the mechanical designer to work from the actual window specification, orientation and shading. A thermostat on an interior wall does not tell the whole story of sitting beside the glass.
Before choosing equipment
Calculate the demand.
Then choose the system.
Load
A heating and cooling load calculation describes the building’s demand under stated design conditions. DOE warns that rules of thumb can produce oversized systems, with unnecessary expense and frequent cycling.2
Capacity
Equipment selection then uses the loads, local design conditions and manufacturer performance data. ACCA’s Manual S addresses this step. The nominal capacity on a brochure is not the complete selection method.3
Delivery
The air or water must reach the rooms as intended. Ask how distribution, controls and installation will be checked. Buying the equipment is one stage of making the system work.
A quieter night.
A bedroom makes modest demands of the people around it: let someone sleep, let someone else get up, keep ordinary sounds from taking over the room. The mechanical brief deserves the same care.
Discuss background sound, air movement at the bed and the location of return grilles before the room is finished. Ask whether doors will normally be open or closed. A design that relies on an open door should not surprise the person who sleeps behind it.
Zoning can help rooms follow different schedules, but a larger zone count is not an achievement by itself. Ask how the proposed equipment behaves when only the smallest zone needs conditioning. The designer needs to reconcile that demand with the equipment’s operating range and distribution requirements.
A simple set of controls can be a luxury. Agree on the everyday actions, the guest settings and who can change them. A house should not require its owner to become the only person capable of making a bedroom comfortable.
An indoor pool introduces a different moisture environment. Its photograph tells us nothing about the installed equipment; a comparable room needs a specialist design brief of its own.
Warm floors are
one part of comfort.
Radiant floor heating can be appealing in a bathroom or a room where bare feet meet stone. Review the floor assembly, finish and controls together. Ask how quickly the proposed system responds and how it will work with the rest of the heating strategy.
Heating the floor does not by itself provide fresh air. DOE distinguishes whole-house ventilation from intermittent kitchen and bathroom exhaust. A balanced ventilation system brings air in and takes air out; energy-recovery equipment can reduce the associated energy loss. The appropriate arrangement belongs in the whole-house design.4
Ask the team to explain heating, cooling, ventilation and moisture control separately, then show how the systems interact. This is especially useful for homes with pools, substantial cooking exhaust or rooms used only occasionally. One attractive device is unlikely to answer every part of that brief.
Living with the result
Ask for a demonstration.
Before handover, walk through the controls with the installer. Ask for the commissioning information appropriate to the system: what was measured, which settings were established and what remains to be checked in another season. Keep the equipment list and maintenance instructions where the person caring for the house can find them.
Open the filter access. Find the shutoffs. Ask how a major component will eventually come out. These questions are easiest to answer before a beautiful cabinet or a finished ceiling makes access difficult.
Then spend time in the rooms. Listen when the system starts. Notice the air at your usual chair. Good mechanical design becomes persuasive through ordinary use, on the mornings when there is no reason to think about it.
Builders, since 1954.
More About Hobbs
Hobbs, Inc. has been building and renovating homes since 1954. The Journal draws on that work and on conversations with architects and craftspeople about the decisions behind a finished home.
Discover HobbsSources and conversation
For a closer look
- Hobbs Conversations: Super Houses
Scott Hobbs and Robert Cardello, April 16, 2021. Checked against the supplied full transcript. Speakers are sources, not authors; historical prices are not current allowances.
- DOE: Proper Sizing of HVAC Systems
Load calculations, oversizing and equipment selection.
- ACCA: Manual S, Residential Equipment Selection
Selecting equipment using loads, design conditions and manufacturer data.
- DOE: Whole-House Ventilation
Whole-house ventilation, local exhaust and balanced or energy-recovery systems.
A few practical questions
Do more zones always make a house more comfortable?
No. Zones should reflect room use and exposure, and work with the equipment and distribution design. Ask how the system operates when demand is low.
Does radiant heating replace ventilation?
No. Heating and outdoor-air exchange are different jobs. The design needs to address both.
What should an owner receive at handover?
Equipment information, operating instructions, service requirements and the project’s testing or commissioning records. Agree on any seasonal follow-up.
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