After thinking through the priorities for the home renovation project, it came time to begin getting more specific on what we want to do to the house. To make the project feel more manageable, I tried thinking about the different systems of the house separately. I'm all too aware that each system affects the others, but it's just too much to attempt to think about the entire house all at once, at least at the outset. So instead I would begin addressing each system and then later attempt to put them together and reconcile/optimize inter-relationships.
But first, the briefest of overviews about the house:
- Year built: 1963
- Lot size: 5200 square feet
- Building conditioned area: 1400 square feet
- 3 bedrooms, 2 baths
- Attached slab-on-grade garage, house itself on vented crawlspace
Some of the systems of the house that I knew I wanted to address in order to reduce energy consumption and improve comfort and health:
- building envelope (i.e., the boundary that separates the out-side from the in-side)
- ventilation & indoor air quality
- domestic hot water
- space conditioning
Here I'll just give an overview of what I'm thinking for each system. In time, a description of the plans for each component in detail may merit its own wonktastic post.
The "building envelope" is the technical term for the boundary that separates the inside of the house from the outside. Ideally it's continuous and robust, but usually...it's not. The building envelope does two main things: 1) it forms an air barrier to keep the inside air in and the outside air out and 2) it insulates the inside from the outside to keep the house warm in the winter and cool in the summer. There's lots more to say about the building envelope, but this is not the place.
As for our house, currently only the ceiling is insulated, the walls and subfloor are not. None of the house has been air sealed, particularly. It's pretty drafty. There's a test to measure just how drafty it is, and after you have that number you can use it both to measure your progress in air-sealing the house and to compare it to other houses. We'll talk more about this test later.
I'd like to get the ceiling and walls insulated to levels similar to those required in new California homes. I'm ambivalent about insulating the subfloor in this climate. The crawlspace provides free cooling in the summer and isn't much of a liability in winter. Also in LA, we don't really have winter, we have "winter." So right now I'm leaning towards not insulating the subfloor, but my position may evolve (as the politicians say). I'd like to get the house's air sealing down to around the upper limit allowed in new California homes. What that number is and how to go about achieving it may be a subject for a later post.
Ventilation and Indoor Air Quality (IAQ)
Quick primer: There are two main types of ventilation in residential buildings: local exhaust ventilation and general (aka "whole-home") ventilation. Local exhaust ventilation removes pollutants being generated from specific sources in the house. Rooms in the house that commonly need local exhaust are bathrooms, the laundry room, and the kitchen. Also the whole home needs to get adequate fresh air. If the building envelope is tight, then there's not much (presumably fresh) outdoor air getting in, so there should be some kind of whole-home mechanical ventilation system. In addition to ventilation, any combustion appliances in the home (gas furnace, gas water heater, gas...anything, fireplaces, etc) also need their own dedicated means of getting combustion air into and combustion pollutants out of the house.
Our house needs local exhaust ventilation in each of the two bathrooms and in the kitchen. It may or may not need whole-home ventilation, depending on how tight I can (or choose to) make the building envelope. As for combustion appliances, our plan is to eliminate them entirely from the house.
Until 2014, the bathrooms in this house had no exhaust fans at all. There aren't too many US climates where you can get away with that, but Southern California is one of them. A couple years ago bath fans were added, but they were installed to just exhaust into the attic, albeit with the ducting pointed in the general direction of a gable vent and a rafter bay vent, respectively.
Venting bathroom fans into the attic instead of to outside is a bad idea (the building code agrees). You're spitting warm, moist air into a semi-enclosed area. If it's the winter the moist air will cool down enough that the water vapor becomes liquid water, and that liquid water will condense on whatever surfaces you've got up there. Insulation, wood, whatever. And organic matter plus moisture equals mold and rot. Think mold spores in your attic getting into your HVAC system and getting distributed throughout the house. Think rafters and ceiling joists quietly rotting away, jeopardizing the structural integrity of the house. It's bad news. Again, because of our warm, dry climate, we get a bit of a free pass. But still.
These bath fans need to be vented directly to outside. I'll probably do that using wall caps on the gable wall. In the kitchen, there's a range hood that's ducted out through the roof. It seems to work well enough, but could be a little more quiet. It's a typical Asian style range hood with a fairly flat bottom and two axial fans. By the way, if you're interested in range hoods, I'll be glad to tell you as much as you'd (n)ever want to know. :)
This is by no means a complete list of the ventilation and IAQ concerns and measures associated with our house, but it's a decent start and will do for now.
Domestic Hot Water
Currently there's a 40-gallon, 60% efficient natural gas water heater in the garage at one end of the house, and both bathrooms at the other. To get hot water in the bathrooms requires flushing out all the cold water sitting in the hot water line. This is roughly 3 gallons of water! In the desert! During a drought! There's so much room for improvement.
Eventually we want to change the system itself to be more efficient, but in the mean time we resorted to some behavioral stopgap measures to at least reduce the wasted water somewhat. We began not using hot water in the bathrooms except for showers. And for showers we put a 5-gallon bucket under the faucet to collect the cold-water-in-the-hot-water-line and use it to water plants.
The plan is to switch out the natural gas water heater with an electric heat pump water heater and to put an on-demand recirculating pump in the farthestmost bathroom. Heat pump water heaters can be 300% (!) efficient and the "recirc" pump will eliminate water wasted while waiting for hot water. These will both run off of electricity generated by electric solar panels installed on our roof. We actually already got the solar panels installed and I installed the recirc pump about a month ago. They both work great! These were two relatively straightforward projects that 1) could have an immediate impact, 2) don't impede other projects and 3) can be done relatively quickly. So, we just went ahead and did them "out of order."
The house currently has a central forced air heating and cooling system. There's a 3.5-ton air conditioner and a 75,000 Btu/hr natural gas furnace, both installed in the mid 1990s and controlled by a non-programmable thermostat. We haven't used either system since moving in.
The plan is to remove both systems and all the ducting and install a two-zone minisplit heat pump. There might need to be a short run of ducting for the head unit on the south end of the house to condition the three bedrooms. But if there is any ducting, it will be low pressure loss and located inside the building envelope.
Currently the electrical system is slightly undersized and outdated from a safety standpoint. The 100-Amp service panel is original (i.e., 50+ years old) and is made by a company called Zinsco. Some Zinsco electrical service panels are known to have serious and dangerous design flaws that can prevent the system from automatically shutting off when too much power is being drawn. The company went out of business a few decades back. I don't know if our panel is one of the flawed ones, but I don't want to take any chances. Also, none of our electrical outlets are grounded.
Our plan was to replace the service panel with a 200-amp one when the solar panels are installed and then to rewire the house with grounded 3-wire cable. We'll also need to install dedicated 240-volt circuits for the induction range in the kitchen and the heat pump water heater in the garage. We want to eliminate natural gas appliances from the house and run everything off of the electricity generated by the solar panels. When the solar panels were installed, the contractors also installed a new 200-amp service panel. So that part's done.
So that's an overview of the systems we plan do work on. It feels like kind of a lot. But I think (hope) I'm up for it. Other topics to be considered are budgeting and sequencing the project, permitting, what we might do ourselves and what we will contract out. And how long all this stuff might actually take to get done. Also down the road it might be worth discussing each of these systems for fellow building science energy nerds who are keen on the technical stuff, as well as something about how all these bits work together as a system. Or at least how I hope they'll work. Thanks for reading.