Our gas furnace (80%, forced-air) and gas water heater are ready to be replaced (I had them installed in 1992), and we're shopping for as much efficiency as we can afford, aiming at a heat pump if possible. Because we're looking for efficiency, I've been asking contractors about inverter-driven heat pumps like the Carrier Infinity Greenspeed, also Daikin or Mitsubishi are candidates. We've looked into geothermal systems (jealous of the one that one of my siblings has), but have both space and financial constraints. Can't afford one of those Daikin Altherma systems, either....
A little background: Home is in Oregon (Portland area), built 1978, 1890 sq ft of conditioned space, 2 floors. Upper floor is all living area, lower story is garage, laundry, family room (finished walk-in basement). We've recently had attic air sealing done and attic insulation added, and have done some window sealing, current CFM50 number is 1800 (down from 2900 before we did all the sealing work). Energy audit report thinks we have 17000 BTUH heat load, 23000 BTUH cooling load, after all our improvements (modelling software used was Recurve).
One contractor's load calculation came up with 26250 BTUH for heating, 23600 BTUH for cooling. They initially recommended a 3-ton Greenspeed heat pump, but were willing to go with a 2-ton unit when I asked. Another contractor came up with a 2-ton size for the Greenspeed heat pump, so I'm beginning to think that's in the ballpark of a correct size. A couple options included 2.5- or 2.6-ton Daikin inverter-based systems.
As an aside, our last 2 years of utility bills (combined gas & electric) have never exceeded 17000 BTUH equivalent. In the cooling season we've been using a couple 5500 BTUH window air conditioners for a few hours on the hottest summer evenings until we can open windows and use portable fans to cool the place down, so are looking forward to being more comfortable on the few hot days or weeks we get here.
Before our air-sealing & insulation work, we ran our furnace fan all the time, due to dust allergies in the household (old system has a Honeywell electronic air cleaner, though I replaced the cells a year or two ago with a 4" media filter). Once I discovered how much money the furnace fan was costing (at about 390 watts measured), I installed a fan timer to cycle it on only 35% of the time. We've been running this way about 4 months, and discovered a "new" problem when the weather got warm here (80-90F) for a few days. Without the fan running all the time, there's a big temperature difference between upstairs and basement (big difference in solar gain). So upstairs, where the thermostat is, it could be 70-75F, thus heat never comes on (setpoint is 68F), but it still feels pretty chilly in the basement. We didn't have much of a difference, if any, in the full-on heating season, so now we're thinking about zoning the basement at the same time that we replace our systems (and especially since we'll have central air-conditioning with the heat pump system, as there's a big diff. in heat gain between the two floors).
Another aside: Our old furnace is way too huge (110000 BTUH input), but it looks like nobody makes a gas furnace small enough for our load anyway. I originally thought we could get a 90%+ gas water heater and use that for backup heat in a variable-speed air handler, but there is no such beast from Carrier to match with the Greenspeed H.P. So Plan B is to go with an all-electric air handler, though I expect we'll seldom need backup with an inverter heat pump in our mild climate.
I know that's a lot of verbiage, but from reading this forum I gather that you all like having lots of background info rather than having to do a bunch of guesswork. So now I come to some questions about air handler, sizing, zoning, and alternatives.
(1) For the best HSPF ratings, the charts show matching a 2-ton
Greenspeed outdoor unit with the 5-ton air handler (I can't see
any matching gas furnaces that give the HSPF of 13). Are there
any down-sides to using the -006 fan coil with the 2-ton condenser?
(2) Am I nuts for going with a 2-ton unit here? My thinking is that a
3-ton unit will not be able to ramp down low enough (40% of 3 tons
vs 40% of 2-tons) in cooling season, especially if we go with 2 zones.
We do have a fireplace and a wood stove we could use if there's an
extended spell of colder-than-usual weather (if we want to avoid
hitting the expensive heat strips). The "shoulder" heating seasons
don't need much heat here either, and I'd be concerned that a
too-oversized unit would be cycling on & off (and again, even more
so if we add zoning). Am I off base with the above?
(3) We've got a couple of prices on the basement zone, and also an
alternative solution (below). Is zoning likely to be more expensive
to add on later, as compared to doing it at time of installing the
(4) One proposal recommended a Daikin slim-duct system, with four
zones sharing one outdoor unit. I think this is a VRV-III system,
and the cost is in line with the Greenspeed split system without
zoning. My main concern with this approach is the relatively low
HSPF numbers (around 8, 8.5, or 8.8, depending on indoor unit),
and loss of central air purifier options. Any opinions?
(5) I've been asking contractors about a 100% outside-air economizer,
to use for night-time cooling/purge of the house. I work with
computer datacenters and in our climate using outside air instead
of air conditioning is real big right now. We do pretty much that
with our house now, but pollen allergies and security concerns make
it tough to do that with just open windows. I'm aware of the
NightBreeze system, but that won't work with the Greenspeed
heat pump. So far contractors have been reluctant to quote on
this type of system, unless I can find something to buy and pay them
to install. Any suggestions?