Any home heating and cooling techs here?
#2737474
01/28/20 05:16 PM
01/28/20 05:16 PM
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Joined: Feb 2005
Posts: 957 MI, Lapeer
maximus
OP
super stock
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OP
super stock
Joined: Feb 2005
Posts: 957
MI, Lapeer
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I need some tech input on a new furnance and ac unit for the house. I had two different companies come out and give me a quote for replacement equipment. I currently have a 100,000 btu furnance and 5 ton ac unit. The house is a two story 3,000 square ft home. One company said I need a 110,000btu furnance and 5 ton ac unit, the other guy said I need a 90,000btu furnance and 2.5 ton ac. He said to go with smaller furnance because my 100,000 unit is short cycling, because it is too big for the house. He also said it is more efficient to go smaller with the ac unit and have it run longer for more even cooling between the upstairs and downstairs. There is a $2,500 cost difference between the quotes. What is the correct size units for my home? Confused after talking to these contractors. Please clear things up for me. What's more cost effective for fuel and electricity? Thanks
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Re: Any home heating and cooling techs here?
[Re: maximus]
#2737507
01/28/20 07:34 PM
01/28/20 07:34 PM
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Joined: Jan 2003
Posts: 20,773 A collage of whims
topside
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 20,773
A collage of whims
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Likewise, I'd like an honest opinion on my deal: 1650 SF, currently electric forced-air heat. Power goes out on occasion during winter. Local generator guru says 1st priority is switch to gas heat. I have natural gas. One of the things I wonder about is if there's no electricity, how does a gas furnace light off? (As you can tell, I'm pretty ignorant on the topic ) Apologies for the hijack, hope there's a HVAC Stu here...
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Re: Any home heating and cooling techs here?
[Re: topside]
#2737522
01/28/20 08:42 PM
01/28/20 08:42 PM
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Joined: Jan 2003
Posts: 4,270 Morrow, OH
markz528
master
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master
Joined: Jan 2003
Posts: 4,270
Morrow, OH
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I can only share my experience.
My Mom needed a new furnace last year for the downstairs and upstairs - 2 apartments. Bottom significantly bigger than the upstairs. Furnaces were from around 1967. Heating guy says the furnaces were oversized so we split the difference between the calculations and what was installed. The results were very good. Asking around found out that in the past the calculations were not very accurate so everyone oversized furnaces.
Oversized furnaces are not good. My Mother in Law's gas furnace is oversized and short cycles. It is not pleasant heating because of it.
On the AC side, 5 ton seems too big and 2 1/2 ton seems too small. I'm in Cincinnati 2 story 1900 square feet and have a tight house and have a 2 1/2 ton heat pump. Seems about right.
I would lean towards the smaller units.......... Maybe 3 ton on the AC.
Last edited by markz528; 01/28/20 08:44 PM.
67 Coronet 500 9.610 @ 139.20 mph 67 Coronet 500 (street car) 14.82 @ 94 mph 69 GTX (clone) - build in progress......
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Re: Any home heating and cooling techs here?
[Re: maximus]
#2737599
01/29/20 04:48 AM
01/29/20 04:48 AM
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Joined: Jul 2003
Posts: 2,344 Cincinnati, OH
6T6Cuda
top fuel
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top fuel
Joined: Jul 2003
Posts: 2,344
Cincinnati, OH
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Go with the one that did a Manual J calculation (which I assume none of them did or they would explain it to you). Here is a presentation I found real quick that appears to explain it: https://www.energy.gov/sites/prod/files/2013/12/f5/webinar_hvac_calculatingloads_20110428.pdfbasically, you calculate the the loss through the walls (based upon the insulation, windows, size of the external walls), roof, etc... the area the house is in (the need for heating and cooling based upon outside temperatures), and it will calculate the number of BTU of heating and cooling you need; then you can size up a "hair" from there to account for the non-seasonal days, or when the load changes quickly. Rules of thumb work, but it is very easy to get it wrong because they do not take into account many important factors, such as the condition of the house (insulation, etc...) or area in the country (which obviously makes a difference).
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Re: Any home heating and cooling techs here?
[Re: 6T6Cuda]
#2737621
01/29/20 08:56 AM
01/29/20 08:56 AM
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Joined: Jan 2003
Posts: 5,138 East Aurora (Buffalo) NY
RoadRunner
master
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master
Joined: Jan 2003
Posts: 5,138
East Aurora (Buffalo) NY
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Go with the one that did a Manual J calculation (which I assume none of them did or they would explain it to you). Here is a presentation I found real quick that appears to explain it: https://www.energy.gov/sites/prod/files/2013/12/f5/webinar_hvac_calculatingloads_20110428.pdfbasically, you calculate the the loss through the walls (based upon the insulation, windows, size of the external walls), roof, etc... the area the house is in (the need for heating and cooling based upon outside temperatures), and it will calculate the number of BTU of heating and cooling you need; then you can size up a "hair" from there to account for the non-seasonal days, or when the load changes quickly. Rules of thumb work, but it is very easy to get it wrong because they do not take into account many important factors, such as the condition of the house (insulation, etc...) or area in the country (which obviously makes a difference). Being an engineer, this is what I did. I worked with contractor while we were remodeling the house. We had the house extremely well insulated, R60 in attic, R-15 (limited to existing walls) to R-23 in walls. House is 2600 sqft. Ended up with a 90,000 btu high efficiency unit with variable speed blowers. The furnace automatically slows the blower or speeds it up depending on thermostat set pint and temperature. I did a similar calculation for the garage when i added heating system (radiant floor heat). I ended up with 60,000 BTU water heater which is a tad undersize for cold winter months based on the calculations. But for a garage, it works well. Garage is 2x6 wall so R-21 in walls and R-60 in ceiling rafters and about 1600 sqft room space. For A/C we have a 2.5 ton unit. And I think thermally its fine. The distribution system for the furnace/ a/C isn't optimal so the two front upstairs rooms don't get adequate cooling in the summer. I may install some booster fans. Its not an issue with heat, because heat rises and the upstairs room get a lot of residual heat up from the stairway.
68 Road Runner (383/4speed, post car w/decor pkg) - Major Project 69 Road Runner w/472 Hemi & 4 speed. 70 Challenger R/T SE EF8 w/ V9J, U - A32 - Major Project 2023 Ford Mach 1
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Re: Any home heating and cooling techs here?
[Re: RoadRunner]
#2737739
01/29/20 02:29 PM
01/29/20 02:29 PM
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Joined: Jul 2008
Posts: 30,424 Florida STAYcation
dOrk !
The village idiot's idiot
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The village idiot's idiot
Joined: Jul 2008
Posts: 30,424
Florida STAYcation
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I have become somewhat of an educated consumer in this field ... Don’t have to worry tooo much about heat down here but AC is a must. I like the idea of slightly undersized! Gets the humidity out of there bester
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Re: Any home heating and cooling techs here?
[Re: topside]
#2738320
01/31/20 06:57 AM
01/31/20 06:57 AM
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Joined: Mar 2003
Posts: 9,099 Rogue River, OR
Jeremiah
master
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master
Joined: Mar 2003
Posts: 9,099
Rogue River, OR
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Likewise, I'd like an honest opinion on my deal: 1650 SF, currently electric forced-air heat. Power goes out on occasion during winter. Local generator guru says 1st priority is switch to gas heat. I have natural gas. One of the things I wonder about is if there's no electricity, how does a gas furnace light off? (As you can tell, I'm pretty ignorant on the topic ) Apologies for the hijack, hope there's a HVAC Stu here... You still need the generator for the blower, thermostat, etc. Switching the furnace to gas will take a 5-15kw load off of your emergency power needs. You could likely get away with 10-12kw gen instead of a 20-40kw set. Thats essentially 2-3cyl territory until you get to 20kw and the 4 cylnders enter the lineup.
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