Up until recently, residential architects varied in their knowledge of heating and cooling systems. Many architects whose focus is primarily one-off, custom residential projects, have simply assumed some form of conditioning and then left the details to their contractor. Finalizing the details may not occur until late in the project, long after the opportunity for building optimization has passed.
What most people also don’t realize is that the manner in which a system is installed and configured can have a dramatic effect on how much it can deliver. Most private residential projects haven’t budgeted for a separate mechanical engineer upfront to optimize efficiencies among systems or to suggest additional measures during the design phase.
Beyond that, of course, there’s another reason for California architects to start paying closer attention to systems upfront: Title 24 energy compliance. The new energy code is stricter, and the default assumptions are no longer good enough for some homes to pass. The Title 24 is typically done when submitting to Planning, at the end of Schematic Design – long before anyone thinks about the furnace other than to say, “Oh yeah, we were going to keep the existing furnace and ductwork from 1956.”
What happens to your Title 24 when you don’t plan ahead?
If you don’t plan ahead, you could learn of expensive additional measures only on the day of the planned submittal, and end up making important trade-off decisions in haste. We are seeing cases where our clients (other architects) had carefully scoped the project budget and they depend upon being able to reuse existing elements such as windows. However, if the project requires the performance method of Title 24 compliance, and we have to model the whole house, those existing windows can make compliance all but impossible to achieve.
Same thing with systems. Once a house is already teetering on the brink of not passing, we need to look for measures to improve performance, and something’s gotta give. You could end up having to insulate more than you’d planned, or replacing a furnace with a more efficient model, or replacing more windows than you anticipated. Yes, we could tell you to shrink the glazing (gasp!) but this would compromise the design intent, which we try to avoid.
Typically we don’t even get information on existing windows or walls, and we have to assume the worst. We’ve also had to work hard to convince people that window efficiency really does make a huge difference, especially now. And, even if we agree on performance numbers that are workable, the project is very sensitive to last-minute changes in the field. We’ve had to add HERS verifications in a number of instances for additional “compliance credits”.
What needs to be known about systems upfront for Title 24 compliance?
First, it’s essential to know the basic system type and configuration. Is it a gas furnace or hydronic heat? A split system with A/C and a heat pump? Is it a tankless water heater or standard 50 gallon storage, or tankless with indirect storage tank? If you have radiant heating, is there a separate water heater for that? How many heating zones are there?
One reason is that some of the above-mentioned compliance credits aren’t available for all system types – you can’t use the HERS duct testing credit on a ductless hydronic system, for example, and you can’t verify refrigerant levels in the A/C system if there’s no cooling installed. Discovering something like this during construction might be one reason to have to re-do the Title 24 report, and you’d have to make up those lost credits somewhere else in a way that maybe you hadn’t planned or budgeted for.
Next, you might have to provisionally select unit manufacturers and models, so that their efficiencies can be used as inputs for the software model. If it turns out you need a higher efficiency model than you’d planned, you at least have time to do some pricing to determine whether it makes more sense to upgrade the system, or perhaps to take other measures elsewhere.
Not all manufacturers post the efficiencies, or sometimes they don’t publish the right ones for Title 24. It can take some time and research to establish what numbers to use, so that these inputs are defensible in the case of an audit. In a nutshell, the main inputs are:
- Gas furnace – AFUE; BTU per hour; default is .80, but you might have to go with .90 or better
- Split or heat pump package system – Heat pump HSPF; default is 7.7; 8 and above are better; goes to 11
- Electric heater – Don’t use this if there’s an alternative. Penalties in Title 24.
- Cooling – SEER; 13 is the minimum; 15-18 is good; however, cooling isn’t as important in this area as it is in SoCal. Many of our Title 24 projects don’t even have A/C.
- Water heater – Energy Factor and for hydronic heating, Recovery Efficiency; tank size; BTU per hour.
- Hydronic – See under water heater.
A house of cards… or what happens to your Title 24 compliance when systems are an afterthought
On projects that are severely constrained in budget and scope, we have had to dig very deep to find measures that are both acceptable to both architect and owner, and which also yield enough performance boost to push the house back into compliance. Usually it’s not just one measure, but a combination of measures all taken together. If any one of those measures is eliminated or altered, then we have to start over – and hope that we can think of something else.
If these measures include HERS tests, then it’s very important that the house is able to pass these tests. This takes coordination with the builder, and assumes quality construction practices. If for some reason these tests can’t be performed, then again we have to make it up elsewhere.
Later in construction it gets even harder to compensate for a change, because measures that might have been possible earlier on are no longer an option. For example, one alteration we worked on was constrained to using single paned clear glazing for “historical reasons”. We had to call out every other measure possible, including replacing the systems, because the one thing that would have made the most sense – better windows – was non-negotiable.
A few answers from Jeff King, Bay Area Green Builder
Of course Title 24 is not reality! There are many more factors that influence efficiency and comfort that are NOT recognized within Title 24 (yet) and it’s helpful to know about them because they’re also important to factor into the design early on. We chatted with Jeff King , a Green Builder whom we’ve interviewed previously, for a reality check on what really works. His experience is mainly in and around San Francisco, working mainly with forced-air and radiant heating systems. His common-sense approach is to use high-efficiency systems and make sure that they’re properly configured and installed.
[Within the interview, my comments are shown in bracketed italic – RF]
How do you size a heating system correctly?
Jeff King: For heating and hot water delivery systems, the systems need to be properly sized – which most are not. Most systems are grossly oversized! This means they don’t operate as efficiently or as comfortably. It’s hard to quantify exactly how many homes have oversized systems, but I would not be surprised at 75%.
Of course most subcontractors rely on a thumbnail view and their own experience of what has worked in the past. For example, the sub might consider the floor area, number of bedrooms and say, “Let’s go with an 80,000 Btu furnace,” when actually, a 40,000 Btu one would be just fine. For replacement systems, subcontractors will just drop in an 80% efficiency system that’s a third to twice as big as what’s really needed, just because that’s what was there before.
In some cases, sizing may be limited by available equipment. For example, you usually can’t buy a gas furnace that’s less than 40,000 Btu, although models with a modulating gas valve can operate in a range from 20,000-60,000 Btu.
How good is the typical installation for forced-air heating systems?
Jeff King: The other important issue is quality of installation. This includes layout and location of various system components. If the layout is an afterthought, it might end up being a lot less efficient, even if the units are top of the line.
[One thing that other mechanical experts have stressed is that right-sizing the ductwork for the system that is installed is as important as minimizing bends and duct lengths. If you replace a system but plan to keep the old ductwork, take a close look at what you’ll be re-using. – RF]
Jeff King: For forced-air systems, include manual dampers at the plenums for all heating ducts to aid in balancing the system. Sometimes one portion will draw air differently than another. The goal is to have less than a 3 degrees of temperature difference between rooms.
You can get high-performance heating registers, too, but not at Home Depot. The cheaper ones don’t mix air appropriately. You need scooping lovers. A good register should also be directional according to its position in the room. I see bi-directional registers put up against a wall – why? Floor-level registers should mix the air up, while ceiling registers should mix it down.
Ductwork should be sealed with mastic and tested for air leakage. We test all our systems to 5% leakage, because we want to be sure it was done right.
Other aspects of how the system is installed include register locations and duct layouts. You might be able to reuse portions of the old system, but if you start moving walls, then you might have to redo other things as well. This is especially important for contemporary architects, because forced-air heating doesn’t lend itself to ultra-modern open designs. In fact, modern architects often default to radiant heating, because they don’t have to design around bulky ductwork. However, radiant flooring isn’t always a good fit for every client’s need.
Architects don’t need to know it all themselves. What architects need to do, though, is consider system requirements at the Design Development phase, not at the construction phase. If you wait until construction, sometimes the architect has to re-design things like duct chases, because you can’t always re-use all the old stuff.
Is on-demand water heating always better?
Jeff King: There’s a knee-jerk “green” reaction where people say things like, “I want an on-demand water heater!” Well, if you’ve got a 5,000 SF house with three stories, and bathrooms on either end of the house that don’t adjoin in any way, on-demand water heating is the WORST!
Same thing with radiant flooring. It’s supposed to be more efficient, and sometimes it is – if you want your home to stay at a steady temperature of 68 degrees 24-7-365. But if you like to sleep in a cold house, and some people do, radiant heat is not so great, because it takes too long to heat back up in the morning.
What makes for an effective hot-water installation?
Jeff King: With hot water delivery, it doesn’t matter whether it’s storage or on-demand (tankless). In fact, I won’t install on-demand water heaters unless it’s a hybrid. Hybrids are essentially on-demand but they do have a small storage tank, typically around 2.5 gallons or so. My favorite model is the Eternal Hybrid. You can use it for heating, too, with radiant flooring or hydronic air handlers.
The Eternal Hybrid is 98% efficient. We include a normal recirculating system and pump, but not on a timer. Instead, the pump is motion-activated when someone goes into the shower, with a thermal sensor at the point of use (if the person doesn’t shower immediately, the heater only kicks back on if the pipe goes below a set temperature of say 90 degrees, assuming the water’s at around 110-120)
When we are installing new pipes, we insulate all the hot water pipes all the way to the point of use. Insulated pipes hold the temperature a lot better.
Even better is manually activated water heating. We haven’t talked many clients into this but we did do it on one job where we used motion-activated sensors in the bathrooms, but had a manual activator in the kitchen. It only takes about 30 seconds to heat up the water.
On-demand recirculation pumps are good for tank-style storage too, for water conservation.
How do you account for the heating system during the design phase?
Jeff King: For forced air systems, you need space for the ductwork. Architects should talk to the contractor during design development, and they should consult with a mech engineer early on. Not just a subcontractor, but an engineer. Sometimes you can just thicken a wall or widen a chase, although you might sacrifice some living space.
Other design elements can affect comfort as well, such as large expanses of glass on the north or south walls. Glass on the north can get chilly, while glass on the south of course can cook you in the summer if it’s not shaded. And don’t place the thermostat in direct sun.
The more modern the design is, the more important the systems become, because you can’t leave them as an afterthought. [You don’t want unsightly elements intruding into an ultra-minimalist design. – RF]
Louis Kahn designed servant spaces and special half-height floors for mechanical systems in some of his buildings.
Jeff King: That’s an engineer’s way of thinking and it’s great. You need a lot of dough, though!
How do you choose the right system for each project?
Jeff King: Here’s what I do.
- Ask the client about their lifestyle habits first. Do they want to shut off the heat at night? Or only keep certain rooms warm? Individuals have different comfort needs, too; some people like it cold, while others can’t tolerate it. Depending on which portions of the home are used, when, and by whom, I might use a 2-zone system, or even a split system.
- Understand how involved the clients want to be with the complexities of their system. Do they want a lot of operational control or a one-button system that’s mostly running in the background?
- Review the furniture layout. This is important for forced-air systems, because you don’t want a register right next to a 400-year-old antique! And you don’t want heating registers right over someone’s bed. That’s very uncomfortable and unhealthy, too.
Architects can do this, too, and then consult with a mechanical engineer who can help them figure out not only the type of system, but what configuration is most optimal.
[Sometimes we get Title 24 projects where the client decides later on to go with a different type of system – usually changing from forced air gas to radiant. However, changing the system type or configuration later on can require re-calculating the Title 24 – so try to anticipate what systems are being considered and at least do a rough check for the viability of each one for Title 24 compliance.
Will anyone actually notice if you fudge things on the report? Well… first of all, if you’re going for any green certifications like GreenPoints or LEED, there’s a good chance the energy report itself will get audited. If you are going for the New Solar Homes Partnership, the report will definitely be audited. And, back to our topic of systems here, the system types and efficiencies are shown on the Title 24 report and it’s fairly easy for an inspector to spot when a furnace shown as .93 AFUE is actually .80.
Will anyone notice if we specify HERS tests on the Title 24 report but we don’t actually perform them? Yes! There is a new process whereby the HERS test results are reported separately and independently, and this documentation must then be provided during final inspection. And once the project’s finished there are fewer options for remediation. – RF]
What about radiant flooring installation?
[Jeff King didn’t have any specific notes on radiant heating installation, but I did find a good example of how layouts and piping configuration can affect system efficiency and heat distribution. – RF]
What about hydronic forced-air instead of heating the air by gas?
Jeff King: There’s a type of hydronic forced air that uses hot water instead of a gas flame to heat the air. It’s a little lower in heat output, but that can actually be more desirable; the system runs more steadily instead of rapidly cycling on and off. Also it’s less drying than forced air with gas – less intense. Generally with heating systems, you want it to run at a low output continuously.
What you don’t want are peaks and valleys. Blowers and thermostats can mean the temperature rises rapidly and then drops off just as quickly.
The most complex system I ever installed of this type was a Phoenix 120-gallon tank storage water heater with advanced temperature sensors and control. This unit provided domestic hot water, as well as heating for 2 hydronic air handlers, plus a radiator in one room that we couldn’t put ducts into. Each of these applications needed a different temperature of hot water, though.
- DHW can’t be higher than 120
- Hydronic forced air needs around 135
- The radiator needs 160 degree water.
We had to draw from different parts of the storage tank.
This forced-air and tank system is something I’m doing on my own house right now. I have to live with it myself for a while, gotta walk the walk.
What about ventilation systems?
Jeff King: I haven’t had to do much in the way of ventilation. San Francisco ventilation requirements are minimal. You don’t need A/C here and most ventilation is “just open a window”. A bathroom fan can meet the ventilation requirements. Whole house ventilation makes sense down in the Valley where it’s hot, or for new, airtight homes with cold winters and hot summers.
Isn’t it wasteful to have to rip out elements like existing windows or furnaces that are fairly recent, but not quite recent enough?
Jeff King: Does it really make sense to tear it all out? I’ll quote Kevin Beck, a trainer at BuildItGreen who says, “I don’t care if the windows are single glazed as long as they seal well against drafts and the walls are insulated. A dual-glazed window here in San Francisco isn’t much better than a really well-sealed regular window.”
Sometimes it doesn’t make sense to tear everything out if it still works well. It’s more about design and getting rid of over-sized pipes or ducts which aren’t needed for more efficient systems. Also remember if the existing ducts may have been poorly installed or sealed, so getting a new unit but connecting it to existing duct pipes might not be enough.
When there’s an opportunity to take an aging system out, then we get the best efficiency we can. The cost is not so much in the equipment as in the labor and installation. The difference between an 80% furnace and a 98% is only about $600 in equipment costs.
What about “alternative” or “cutting edge” or “emerging” system technologies?
Jeff King: I’m not that into the more far-out or experimental technologies. I think more about system longevity. Also I’m wary of them, because what about maintenance? If you install some high-tech invention, there won’t be many people around that even know how to repair it.
The Phoenix water heater I talked about earlier is about the most techno-enabled system we’ve ever installed. Other technologies like ground source heat pumps (geothermal) aren’t great for urban settings because you need land. I haven’t worked with them.
Ross Levy of LSArc<http://www.lsarc-sf.com> designed a system for a Victorian remodel here in San Francisco. The client’s goal is to be NZE and grid independent. [We plan to write a description of this home in a future article. – RF]
About the author
Rebecca Firestone has been working in the Bay Area since 1998 as a technical writer, business content developer, architectural filing lady, marketing director, and sorcerer’s apprentice.