Need help formuating retrofitting stragegy
MacBruins
| Posted in Energy Efficiency and Durability on
Hi, Everyone,
I need help figuring out a path to retrofit/improve my roof and attic.
I live in the inland portion of East San Francisco Bay. The weather is Mediterranean climate. The average hi/lo is 90/55 in summer and 55/35 in winter. DOE climate zone is 3 & dry.
My house is a two-story house, built in 2000 with shingle roof. It has finished vaulted ceilings. The attic is unconditioned. The furnace & heat exchanger for the second floor are in the attic. So are the ducts. The second floor is about 1500 sq ft.
I will get new HVAC systems soon. When they are installed, per local code, the contractor will re-seal all ductworks and wrap all ducts with better insulations. The new systems will be 2 stage 17 SEER AC & 96% furnace.
Beyond that, I want to
(1) add more insulation to the vaulted ceiling. That space just wastes energy, but I can’t get rid of it. So I will settle for wasting less.
(2) better insulate the attic because of the HVAC equipment.
(3) add solar panels with battery storage.
From what I read here on GBA, rigid foam insulation above sheathing seems the best solution for 1 & 2. However, this method means replacing the roof, which is in good shape. And the solar panels have to be installed after new insulation, or re-installed at additional cost.
Is my understanding correct? What are my alternatives? More insulation for the ductwork? My knowledge in improving home energy efficiency is limited, so I appreciate any suggestions. Thanks in advance.
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Replies
William,
I'm not quite sure that I can visualize your situation; you wrote that your house has "finished vaulted ceilings" (which implies that there is no attic) but also that your house has an unconditioned attic with HVAC equipment. I assume that there are two sections of your house, each with a different type of roof assembly.
There are several ways that you can convert your vented unconditioned attic into an unvented conditioned attic. If you don't want to install rigid foam on the exterior side of the roof sheathing, you might consider installing closed-cell spray foam on the underside of the roof sheathing. For more information, see this article: "Creating a Conditioned Attic."
Hi, Martin, thank you for the reply.
Allow me clarify: Imagine a rectangular house with gable roof. The longer walls of the house face south and north. The roof ridge runs from east to west. The house has two rooms. One is on the north side and the other on the south side. The north room has finished vaulted ceiling, so the rafters are hidden behind sheetrock. The south room has flat ceiling. Above the south room is the attic. This is basically the second floor of my house.
The north room is the energy hog. In winter, due to lack of sunlight, high ceiling, and probably poor insulation, it is much colder than the south room. On a sunny winter day with thermostat set to 69, the south room is 73 degrees and the north room is 66.
I started my search to add insulation to the north room. But all I could find is the "rigid foam above sheathing" method. Insulating the attic is my secondary goal. My reason is that when the north room is better insulated, HVAC won't run as much, and energy loss through attic will be reduced.
I did learn about the closed-cell spray foam for attic, but it doesn't help insulating the north room. I feel like I am in a jam here. My only choices seem to be (1) throwing away good roof for new insulation, or (2) installing solar panels, saving a little in the attic but leaving a gaping hole above the north room.
As before, any suggestion is appreciated.
Is it too late to consider a revision to the HVAC plan? If you opt for a heat pump system you can consolidate your investment into one even higher performance unit to cover heating and cooling while avoiding the climate impacts of natural gas. If you are planning envelope upgrades, you can save money on the HVAC system by downsizing it for the lower heating and cooling loads you'll have at the conclusion of the project. Then you'll have more money to invest in the envelope.
Hi, Charlie, thank you for your suggestion.
I misspoke in my original post. The new systems I will get are 2-stage heat pumps with furnace as backup. I believe they will stay in heat pump mode over 90% of the time.
Regarding getting higher performance systems and envelope upgrades, my push in that direction has been frustrating. Although I live in the SF Bay Area where many think they are "greener than thou", I start to suspect the reality is much different. When I asked AC contractors how often equipment is installed in unconditioned attic, the answers were all the time. When I asked who can do manual J calculation, no one knew. When I asked to buy 20 SEER variable speed systems, they didn't want to sell them because the installers would need special training. They didn't even want to sell me heat pumps.
Perhaps I talked to the wrong people, but I doubt it.
If you have other suggestions, please let me know, and I thank you in advance. And sorry for the rant.
Dump the furnaces, heat pumps alone will easily handle your climate (and mine, in Sacramento).
William,
If the north room is that much cooler in winter, it probably has LOTS of air leaks. In standard construction, that probably means the windows and the ceiling. Average-quality windows from 2000 can be very drafty, even if double pane "efficient" windows. Changing them might make a big difference.
Next, are there recessed lights in your vaulted ceilings? These are also likely large air leaks. You can address that and roof insulation from the inside. Take down the ceiling and add 2"-3" of rigid foam insulation on the interior. Change the recessed lights to sealed fixtures, or eliminate them altogether. Go with LED fixtures while you're at it. Tape and seal the foam insulation to make it airtight, and then add drywall. You probably won't notice the loss of a few inches of headroom in a vaulted space.
In your case, an unvented, conditioned attic makes sense (Martin's suggestion, above). The tall wall separating the north room vaulted space and the unconditioned south attic is another big energy hog, usually very poorly insulated and air sealed. Insulating the roof of your attic actually reduces the surface area of your thermal envelope, because it is the third side of the triangle (the vertical wall and the flat ceiling being the other two). The gable end walls add back some area, but I expect you are still better off, especially since this lets you bring the ductwork inside the conditioned space.
Hi William,
I would recommend to continue looking for the right contractor. A ASHP works great in our climate and wouldn’t need a gas furnace backup. The key to making a difference is addressing the home as a system, where each part affects other parts. Perform an energy audit, Come up with a plan, then perform a Manual J and Manual D for after the improvements in air sealing and insulation and duct insulation. Your HVAC system is probably oversized, especially the furnace, which causes short cycling and short blasts of hot air that contribute to uneven heating. So get a right sized Heat Pump of at least 2 stages and SEER 16 or so. Then install everything together, so it performs as designed.
I live in Sacramento CA and recently participated in a utility rebate program by SMUD called H.P.P. I converted can lights to sealed LED inserts, air sealed the entire attic floor, installed a high flow, low static pressure duct system with R8 ducts and metal elbows and Y’s, along with a second return/filter, they removed my oversized 5 Ton A/C and 100k BTU gas furnace and installed a 3 Ton Rheem RP17 3 stage Heat Pump with NO heat strips after months of my research on performance vs value. The new duct system was air sealed to less than 5% leakage and was ran on the attic floor and deep buried in the original R30 blown fiberglass plus another R38 blown fiberglass to completely cover all ducts. The house is so comfortable with even temperatures now, and had continuous runtime last week when it was 106 outside, cycling every 15 minutes or so from 2nd stage to 3rd/high stage, meaning it’s pretty closely sized to the cooling load. I didn’t see a value or ROI on 20 SEER equipment or full variable speed. The Rheem RP17 is the only one I’ve heard of with 3 stage inverter driven compressor and 2 speed or variable option indoor unit. The variable indoor unit is required for Rheem Econet full communication operation if you do zoning on a 2 story. I also looked at Bosch IDS 25%-110% fully variable system, but version 1 didn’t work with zoning. Version 2.0 is now available and a very good value for the specs.
I performed a manual J load calc before this, showing 28k btu heating load and 31k cooling load, as well as blower doors testing before and after. The smallest gas furnace is 40k btu, so the only way to get closer to the heating load was by using a multiple stage or variable speed heat pump. I also received a rebate for switching to a heat pump HVAC as well as heat pump water heater.
My house is 2 story 2735 ft2 built in 1996 with R13 walls, metal dual pane windows, tile roof, slab on grade.
Dave
The contractor I used was Golden Aire HVAC. There is a list of 14 or so contractors qualified for the rebate program on SMUD HPP website. I know SMUD is not your utility, but some of the contractors may be close enough to help you out.
Dave