We have a rental house that's 850 square feet in Riverside County (about 1 hour west of Palm Springs). Summers are hot and very dry. The house is a box, single story, 2 BR/1BA, south facing.
Built in 1952, the house needs a full AC unit and we'll replace the furnace at the same time. A manual J was not performed by any of the contractors who gave us estimates. In addition to the new AC/furnace, we'll change out the last two windows (to vinyl, double pane) plus new insulation in the attic.
Question 1: shall we buy the two-stage? (adding $ and 14.5 SEER upgrade from 13) Or with this small a house and completed upgrades, shall we go with the single stage?
Question 2: is "single-stage" / "two-stage" an option that refers to the furnace or the air conditioner? I seem to have seen it both ways in blogs, etc.
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In case more details are needed, here are the systems the HVAC contractor put together:
TEMPSTAR/CARRIER systems (both)
Single stage system:
Single stage furnace - model: MSL451412A. A 2 Ton capacity horizontal heater. 80% AFUE
efficiency.
Evaporator - coil model: ENH4X24L17A.
Condenser - model: N4A324AKB. 2 Ton. 410-A. 13 SEER efficiency.
Two stage, higher efficiency system:
2 stage variable speed furnace, 80% efficiency.
Evaporator coil - model: ENH4X24L17A (used in both systems)
Condenser - model: NXA624GKA (16 SEER)
This match will produce 14.5 SEER efficiency
Last edited by beenthere; 04-04-2013 at 06:34 AM.
Reason: Price
Designer Dan
It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
Who pays the utility bills? ROI will be zero if rental.
In your climate, ROI is zero no matter what in a small house, moderate climate. You don't have a winter or summer... at least not with much humidity. You need the smallest single stage furnace and 1.5 ton AC (smallest they make). I doubt you need a 2 ton in that climate since it's so dry unless the entire south facing wall is almost all windows without shade. I think 2 stage is a waste in this case. Maybe if it was closer to 1500sqft you might consider it, or if it was your primary residence in a fancy neighborhood. Although all homes are expensive in CA. Heck that little bungalow is probably worth more than my 3200sqft house on a 0.5 acres lot overlooking a river.
I'm not sure anyone makes a 45k BTU 2 stage 80% furnace. No benefit to go to 60k BTU to get a 2 stage since low fire will be about the same output anyway as a 45k BTU so it wouldn't run any longer.
IF it was new construction, I'd suggest a combi boiler and hydronic air handler.
Who pays the utility bills? ROI will be zero if rental.
Good point. The renters pay the electric bills but there is a chance we may move back when we are retired. That could be another 10 years. So our selection is for renters now, but something we'd be happy with if we lived with it.
Ooops... if you 1 hour east (assuming reasonalb traffic) then you past the mountains in the desert I assume? My mistake. Yes, you'll probably need a 2 ton since desing temp in Palm Springs is 113F. Winter design is only 34F, so again, smallest furnace possible will be plenty. I still wouldn't bother with 2 stage only because it's a rental. The EER (effciency at high temrpatures) is usually the same, so there's is little savings to be found in a hot dry climate.
You may want a 3 ton blower which might mean a 60k BTU furnace just so you can install a oversized coil and run airflow higher since you don't need humidity removal. A 3 ton coil and airflow set to 900CFM will give you higher effciency.... if you have large enough ductwork to handle it.
Since your electric rates are high, you might consider a VS blower and a 15 SEER single stage unit for a little higher effciency. A good system will last 15-20 years if properly maintained, so you you'll still be stuck with it after you retire.
10 years down the road, you probably have 5 years left with installed system that you would be paying utility bills on. So 5 years times ( single stage sytems utility bills minus two stage stage utility bills(when you will be paying electric bills)) should be more than what the difference in the cost of the two systems. ROI.
Fact is two stage will save energy dollars. Fact is two stage will have more repairs.
Go with a single stage 14 SEER system probably the best financial bet.
Your AC contractor can chart for you utility costs at different KWH rates so you can see dollar figures.
Ooops... if you 1 hour east (assuming reasonalb traffic) then you past the mountains in the desert I assume? My mistake. Yes, you'll probably need a 2 ton since desing temp in Palm Springs is 113F. Winter design is only 34F, so again, smallest furnace possible will be plenty. I still wouldn't bother with 2 stage only because it's a rental. The EER (effciency at high temrpatures) is usually the same, so there's is little savings to be found in a hot dry climate.
You may want a 3 ton blower which might mean a 60k BTU furnace just so you can install a oversized coil and run airflow higher since you don't need humidity removal. A 3 ton coil and airflow set to 900CFM will give you higher effciency.... if you have large enough ductwork to handle it.
Since your electric rates are high, you might consider a VS blower and a 15 SEER single stage unit for a little higher effciency. A good system will last 15-20 years if properly maintained, so you you'll still be stuck with it after you retire.
Thanks for this info.
We're located west of those mountains (sounds like you know SoCAL geography), so it's not technically the desert. Palm Springs is the fire...we're just the frying pan (a "Mediterranean" climate).
This is new construction as far as there's only a wall heater now...no AC and therefore no ducts. But the house is quite old...it's got asbestos shingles on the exterior walls AND on the floors under the carpets!
Yes, based on my calculations, and accounting for misc incidentals, such as high-heat electronic components and cooking in a south-facing kitchen (YUK) I came up with a 2-ton too (2ton2?? tee-hee).
Good to hear that we needn't get the two-stage but I'm also hearing we'd do better bumping up the SEERs, and not go bottom line/cheapest with any 13 SEERs unit. I'll also ask about upping the coil for a higher airflow volume.
10 years down the road, you probably have 5 years left with installed system that you would be paying utility bills on. So 5 years times ( single stage sytems utility bills minus two stage stage utility bills(when you will be paying electric bills)) should be more than what the difference in the cost of the two systems. ROI.
Fact is two stage will save energy dollars. Fact is two stage will have more repairs.
Go with a single stage 14 SEER system probably the best financial bet.
Your AC contractor can chart for you utility costs at different KWH rates so you can see dollar figures.
I appreciate this feedback. It's also nice to hear that these systems are built to work into the next 15-20 years (the gurus masterminding disposable electronics and appliances for faster turnarounds will have to get working on that. Sorry, is that too cynical? ) Heck, that's year 2033...whoa. Hubby and I may not be around to be concerned with it!
Another factor with ROI is simply inflation costs of electricity. Who knows what we'll be paying by 2033?
I see the consensus is for single stage (keep it simple) but higher SEERs than 13. We'll look at 14 vs. 15 re: rebates, ROI, etc.
I appreciate this feedback. It's also nice to hear that these systems are built to work into the next 15-20 years (the gurus masterminding disposable electronics and appliances for faster turnarounds will have to get working on that. Sorry, is that too cynical? ) Heck, that's year 2033...whoa. Hubby and I may not be around to be concerned with it!
Another factor with ROI is simply inflation costs of electricity. Who knows what we'll be paying by 2033?
I see the consensus is for single stage (keep it simple) but higher SEERs than 13. We'll look at 14 vs. 15 re: rebates, ROI, etc.
I'll give my 2 cents since I'm in the area.
Rental?
80% furnace & 13 SEER condenser. Nothing fancy but I would avoid value line stuff. There will be no payback on heat or air. In that area, 13 SEER vs 14 or 15 won't make much difference. No ROI.
Make sure filtration is handled. Either a filter base or a media filter. Gets windy & dusty there so I'd upgrade filtration. Don't depend on tenants replacing the filter. Do it yourself or hire a company to do it for you. I can't tell you how many times an owner has left a case of filters for tenant to change & they never do.
As for longevity, simpler & basic will outlast all the multi-stage VS stuff. By the time you are ready to retire & move there the system will probably be at the end of it's life. IMO- replace for now- not for future.
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Originally Posted by timjimbob
) Heck, that's year 2033...whoa. Hubby and I may not be around to be concerned with it!
