new hvac quote w/ load calc, but questions

15 years ago

hello,

i recently had a quote for a new hvac system (current is old and needs replacing), however i am reluctant to go with a 4 ton unit. i currently have a 3.5 ton system that the builder spec'd. i have decided to go with a trane unit (15XLi to be specific), but not sure if i should go with the 4 ton that was spec'd. the load calc was only 1 or 2k btu's above 3.5 tons, and a 4-ton seems a tad bit oversized. the rep said this would allow for more airflow, but i wonder if it would also bring more noise. he did look @ ductwork, all checks out. w/ the 4 ton i would get the 4tee3f49 air handler, but he mentioned this will be a tight fit (current air handler is 54 inches and its tight enough--*49 is 58 in.) . i have been doing some research online, and i read that load calc's are only relevant to the extreme outdoor conditions. my house has a lot of shade, and am i wrong to think that 1 or 2k btu's undersized is not that bad? the 3.5 ton 15XLi and 4tee3f40 air handler would fit much better. also, how short can the metal box underneath the air handler be w/o causing issues?

thanks for reading

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Comments (3)

steveskm62
Original Author
15 years ago
i checked the proposal i have here, and the load came in at 44,528 btu's. the home is 2 stories + a basement (total sf: 3500). some vents have trouble getting ample airflow (though most are ok). would a 4-ton blower help this issue? what is the btu output of each unit?

i just thought this would help.
tigerdunes
15 years ago
steve

may i ask area of country/state you live?

this is a HP or straight AC condenser?

how does your current 3.5 ton handle your cooling load?

your configuration for 3.5 ton with 4tee3f40

1384601 Active Systems XL15I WEATHERTRON TRANE 4TWX5042A1 4TEE3F40B1 43000 11.90 14.25 43000 8.60 28200 1

best eff configuration for 3.5 ton

1384605 Active Systems XL15I WEATHERTRON TRANE 4TWX5042A1 4TEE3F49B1 43500 12.10 14.50 42000 8.90 27800 1

or

1382172 Active Systems XL15I WEATHERTRON TRANE 4TWX5042A1 4TEE3F65B1 42500 12.50 15.00 42000 9.00 27200 1

your configuration of 4 ton with 4tee3f49

1385065 Active Systems XL15I WEATHERTRON TRANE 4TWX5048A1 4TEE3F49B1 48000 11.80 14.25 50000 8.70 31200 1 HRCU-

best configuration with 4 ton

1382178 Active Systems XL15I WEATHERTRON TRANE 4TWX5048A1 4TEE3F65B1 48000 12.25 15.00 47500 9.00 30200 1

with a 4 ton XL15i, that would oversize your cooling load only about 10% which is not really a big deal with a var speed air handler assuming the load calc is reasonably accurate.

of course, you have to ask yourself if there is any reasonable opportunity to reduce cooling load with some insulation improvements?

just a few ideas..

IMO
TD
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The design temps used on the load calc (outside/inside): winter (42/70) and summer (97/75). The condenser is on a flat roof in the back of the house. It can be accessed for servicing but wasn't something I could get at easily on my own to check size. As far as original equipment size, I can have my husband climb up tomorrow to try to find a serial number and see if we can confirm the tonnage. It keeps the house relatively cool (we keep the thermostat around 76-78 most days), but not really cold. The ducts are smaller, 5-6" if I'm properly reading the sketch Contractor 3 made, which is what I think he meant when he said the house may be designed for 3/3.5 tons max. As far as Quote 3, that contractor originally quoted us Carrier equipment: a 16 SEER two stage 4 ton Carrier condenser (24ABC748A003) paired with a two stage 4 ton furnace (59TP5A080E2120) for $11,940. He said that he could get a comparable American Standard quote, but it's not a brand he typically reps, and he sent us Quote 3. The Carrier furnaces he quoted us are smaller, so I'm not really sure why the American Standard isn't. We didn't press him for more info yet since we've realized we're in over our head and need some outside advice. The 16 SEER is arbitrary based on the fact that we've been looking at quotes for various SEER (13-21). We've ruled out the high end as too expensive for the energy saving but the 16/17 SEER models seem to offer a decent savings compared to the price difference for a 13 SEER. My husband like Quote 1 because it's the cheapest but the contractor seemed sketchy. It's a big company and the rep offered us a "great deal" to replace "any accessible ductwork" (which is basically none of the ductwork since we don't have crawl space or attic access and everything in in the walls/ceiling) for $2000 so we could upgrade to a 5 ton unit. We like the contractor for Quotes 2, but the $2400 difference between quote 1 and 2 is off putting. The Quote 3 contractor spent the most time with us and did a load calc at our request, but he seems to better understand the Carrier equipment if he's misquoting the American Standard equipment so badly. This is our first huge decision as new homeowners and it's become so confusing. Since we hope not to replace the AC system for enough 20+ years, we're stressed about getting it right.
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steveskm62
Original Author
15 years ago
hi tigerdunes and thank you for the reply. i live in virginia (real close to D.C., so it can get hot and humid but also cool). i have a heat pump. electricity is expensive but its the only option unfortunately. the 3.5 ton seems fine now. it cycles on and off, but to be honest, i dont really know how it handles extreme heat. i think if it wasnt doing the trick, i would know. i like it cool in the house, and keep the thermostat at 72 degrees most of the time in the summer and 70 degrees most of the time in the winter. if the 43000 in the numbers you provided were cooling and heating btu's, then it doesnt look like im too far away from the load calc results. i think it was pretty accurate as i watched him do it on a sheet of paper. i dont foresee any improvements down the road really. if the 4tee3f49 air handler wasn't so tall, i would probably go right ahead with it, but the 4tee3f40 is shorter (as ive been informed) and would fit better. im not sure how short the return air box can be w/o causing a problem. if it can be around 13 or 14" then i think i could go with the 4tee3f49 air handler. so i guess the main issue now is, go w/ a shorter return air box underneath the air handler or undersize slightly. thanks again for the reply. i thought for a bit i may have been oversized since it was cycling more than i thought it needed to at times. humidity control is not bad either.

new hvac quote w/ load calc, but questions

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steveskm62
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tigerdunes

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