My wife and I recently purchased a home built in 1990 but meticulously copied from a home near Santa Barbara built in 1910. The house has two air handler/furnaces in the basement and two compressors located on the south side of the house.
I have the 1990 plans, and they show only one system. But it looks very much to me that the second system was added at the time of construction.
It is a mostly one story home with 15' open-beam ceilings for all 1st floor rooms, except part of the northern first floor has 10' ceinings due to two bedrooms and a full bath being above on a 2nd floor. 2nd floor has 10' ceilings, and HVAC registers come down from attic above.
From 1990 to 2014 the house was approx 3400 sq. ft. In 2014 a guest bedroom and full bath were taken from two of the three tandem spaces in the garage, and now the house is 3700 sq ft.
HVAC System #1: runs all of 1st floor - including the newer guest bedroom - except the master bedroom and the 2nd floor.
HVAC System #2: runs master bedroom on 1st floor and all of second floor.
Both systems are in the basement, which is under the norther east entryway as well as under the two-story part of the house. A large chase (with ductwork, maybe some romex and the exhaust flus for the furnaces and water heater) leaves basement ceiling and heads up through 1st floor, 2nd floor, 2nd floor attic and then daylights above 2nd floor roof.
The entire home (excepting the guest room) is above a large crawlspace where a great deal of duct work lives. and registers in the walls are served by these below-the-floor ducts as there is no ceiling in most of the home (all open beam). Underside of all floors are fiberglass insulated.
Walls are all 1 foot thick (stucco exterior, plywood, 2X6, plaster interior). They are full of pink fiberglass insulation.
Roof is traditional 2-piece clay tile, with paper and plywood sheathing throughout. Structurally it appears to be 2 X 12 rafters on 16" centers with 10" of pink fiberglass insulation between the rafters.
Windows are original 2-pane glass casement. Some are clearly leaking (moisture on the inside).
The heat load (sun) is on the south side of the house, which is where the kitchen and the guest room are located.
Problems I know About:
- All components are original and on their last legs
- 2nd floor gets too hot if you're trying to heat master bedroom even just a little.
- There is no door between 1st and 2nd floor.
- The kitchen and guest bedroom are at the end of a long run on HVAC 1, and guest room has zero airflow so much as I can tell. Both guest room and kitchen are cold.
- The returns for both systems are together in the same spot and seem drastically undersized to my (untrained) eye.
- Master has no return, so door must be left open. Can be a little bit of a bummer when guests are over.
- Just my wife and I live here probably 320 days a year. Kids and spouse/S.O.'s come and stay periodically, but for the most part we don't use the upstairs and guest room.
Unknowns:
- We have not lived here (Inland So Cal) during the summer so we know little about cooling.
- I have replaced all of the bad (some of it rat-eaten) flexible duct work that I've been able to find so far, but I have not tested either system for leaks.
Photos (w/my crude drawings below - sorry, I'm an accountant turned contractor and I can't even draw a stick figure...):
Yellow - where the heat comes from
Red - I'm guessing is the hottest area of the house (and future location of solar panels)
Green - general location of guest room and kitchen
Blue - entryway, with basement below and two-story portion above
Yellow - heat load (a repeat I guess)
Black - location of 1st floor master bedroom
Blue - two-story portion where extra "overflow" bedrooms are located above 1st floor
Garage shot showing roof type and a part of the guest room on the right
Stairs up to 2nd floor landing and bedrooms. No door or barrier between 1st and 2nd floor
Utility Basement
Crawl Space
(Realtor-staged photo) Ceiling
In our last home we went with a high SEER unit with one air handler/furnace, one two-stage compressor and two thermostats for two zones. Added automatic dampers allowed for one zone to work while the other was idle. Not sure if dampers might help the overheating upstairs or not.
I’m open to installing new “trunk” ducts, adding returns or even a
Mini-split for the guest room (although not preferable considering our electricity rates in CA!)