How JustAnswer Works:

  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.

Ask Matthew Your Own Question

Matthew
Matthew, HVAC Technician
Category: HVAC
Satisfied Customers: 2000
Experience:  14 years experience in the HVAC field of service, installation, Manual J & D calculations
6927568
Type Your HVAC Question Here...
Matthew is online now
A new question is answered every 9 seconds

heating 17 year old home 1600 square foot well insulated also

Resolved Question:

heating 17 year old home 1600 square foot well insulated also heating basement do i need a lennox 70000 or 90000 btu 2 stage furnance
Submitted: 3 years ago.
Category: HVAC
Expert:  Matthew replied 3 years ago.

Matthew :

Hello, My name is XXXXX XXXXX I will do my best to help you today.

Customer :

i got three different answers about installing a lennox g61 furnance in my 1600 square foot home 17 years old well insulated and would like to heat 800 square foot basement for living area is the 70000 btu or 90000 btu better it is a two stage 2 contractors said the 70000 and one said the 90000 would be better

Matthew :

They both have aXXXXXblower so either will work it just depends on what type of climate your putting this in.

Customer :

putting it in michigan just dont want to be oversized or undersized at present it one has a one stage furnance

Matthew :

I would go with the 90,000

Customer :

that would be better than the 70000 how do you figure out the calculations on that is it because i want to heat the basement and if i went with the bigger one could i add a 14x14 room in the future

Matthew :

The only true way to know exact is to do a manual J on the house. This requires software that is about 2,000.00 or someone who has had classes on how to do one by hand.

Matthew :

most installers do not ever do a manual J they use rule of thumb Technics which get it close.

Matthew :

600sf/ton

Matthew :

if you have 2400 sqft total that means you need XXXXXfurnace.

Matthew :

The single stage and 2 stage doesn't matter when considering heating BTU's it just determines how efficiently it provides those BTUS

Customer :

what isXXXXXforce what furnance g61 70000 or 90000 the 1600 ranch top floor has vaulting in the living area only basement is small want it heating so we could use it for some living space what would you use if its your home

Customer :

they were going to use 2 1/2 ton air

Matthew :

that would be for the main floor sq/ft

Matthew :

but you said there was another 800 in the basement?

Customer :

yes main floor 1600 basement is just a basement of 800 square feet we would like to heat and do some finishing on to watch tv etc

Matthew :

If you are goign to tap off the existing system for the 800 sq/ft basement then I would want bigger than 2.5 ton.

Matthew :

unless they plan on power zoning the basement off the system

Customer :

probably that power zoning the basement i dont know i will talk to them but what about the furnance size

Matthew :

this G61 is a 90+% furnace so going with 70,000 BTU is more than enough

Matthew :

if you where using an 80% furance i would go with 90,000

Customer :

so the 70000 will be enough to heat the top floor and the basement i know it is two stage but one of the contractors said the 90000 would be better because 1600 is at the top of the 70000

Customer :

at present the furnance is one stage and only 70000btus

Customer :

would there be a problem with using the 90000 instead

Matthew :

no none at all

Matthew :

If it short cycles too much you just go down and block off one burner

Matthew :

Having too much heat isn't as big as problem as having too much or too little cooling.

Customer :

what one would short cycle too much the 70 oe 90

Customer :

70 or 90

Matthew :

For example here in Georgia for a system that requires 4tons of cooling we could put the smallest possible furnace on 40,000 btu and still have plenty but we can't because the smallestXXXXXfurnace is around 90,000 BTU

Matthew :

So we just put the 90,000 BTU furnace in and then block one or two burners off so it is actually putting out around 60,000 or 50,000 btu

Customer :

i dont understand what you are saying what would short cycle

Matthew :

The bigger one would cause short cycling if it was too much heat

Customer :

i see so having too much because the lowest btu it starts with is 66000 mite not be good

Matthew :

But you can always decrease the size of the bigger one. You can't increase the size of the smaller one.

Matthew :

So if in doubt go bigger

Matthew :

If they are power zoning the basement then 70,000 is plenty

Matthew :

If they are just dumping runs to the basement and it gets air anytime the furnace is on for stairs then go bigger

Customer :

just has runs in the basement with that has air vents on them that you can open and close

Customer :

so special power runs or zones i just dont know what to do dont want to be to big or be to small and the furnance always cycling i guy came with a computer and put all measurements in and said 70000 but my husband did not tell him about the basement how much is the top square footage that the g61 70000 can heat

Matthew :

70,000 BTU is perfect for the 1600 sq/ft upstairs.

Customer :

is the 2 and 1/2 ton air conditioner compatible with the 90000

Customer :

what about the basement

Matthew :

exactally.

Customer :

what does exactally mean

Matthew :

if you figure in the basement duct work and sq/ft it really should be at the very least 3 ton with a 90,000 furnace.

Matthew :

I mean what about the basement

Matthew :

when I say exactally

Customer :

ok so i need to go back to the drawing board i have had differences because of this furnance it is starting to get to me i need to decide by tuesday

Matthew :

All your doing when you take runs off the furnace and stick them in the basement is stealing the BTU needed for upstairs so the upstairs takes longer to heat and cool then it should based on the size system installed. If you are putting in new equipment you should go up in size to accommodated for this extra 800 sf that is now being heated and cooled.

Matthew :

Chances are you currently have a 2.5 ton system with a 70,000 BTU furnace and they quoted changing that system with the exact same size system right?

Customer :

i had 70000 single speed and i guess that was the same with air everyone says two speeds are different what exactly can the lennox 70000 handle in square footage

Customer :

man you really have to investigate everything yourself to get a good answer you know what i mean

Matthew :

That system that you have on the house now was designed for the upstairs 1,600 sq/ft only. So while you have the chance you need to up the size of the system to accommodated this extra 800 sq/ft that wasn't there when the original system was put in. And that would be a 4 ton air conditioner with a 90,000 BTU furnace. You could get away with a 3 ton air conditioner and a 90,000 furnace because a basement doesn't really need much cooling in the summer it stays cool.

Matthew :

It's hard to put a number on sq/ft heating BTU. It really depends on the tonnage drive of the furnace.

Customer :

so when they told me the lennox 70000 could easily handle 1800 square feet they were probably off.

Matthew :

70,000 BTU furance can handle up to a 3 ton a 90,000 can handle up toXXXXX/p>

Matthew :

no I wouldn't say they were off at all. 70,000 btu can handle 1800.

Matthew :

70,000 btu furnace hasXXXXX so at 600sqft/ton that is 3 ton for 1800 sqft

Matthew :

I would't go much more than 2,000 on a 70,000 btu furnace because then you would require a higher ton blower.

Matthew :

but you have 2,400 sqft of heated area with the main floor and basement

Matthew :

so you need a furnace that has aXXXXXblower. furnaces go from 3 ton and then the next size up is 5 ton meaning it handles up to 5 ton.

Matthew :

the 90,000 btu has this size blower.

Customer :

if this was your house then you would go with the 90 i forgot to tell you the basement is open to the house no door on it we want to put a door on the basement would the 90 over power the home

Matthew :

no it would not

Matthew :

especially in Michigan.

Customer :

i have to tell you the guys who told me to put in the 70 one said the basement would heat fine after i called him

Customer :

i just dont want to make a mistake on this investment

Matthew :

it probably would, it probably would heat too much

Matthew :

The upstairs would be what struggles

Matthew :

The thermostat is upstairs so the furnace would run until the upstairs reached temperature. The basement is underground so it doesn't lose it's heat as fast and doesn't require as much to keep it warm.

Customer :

your taking about the 70 now

Matthew :

So as the upstairs runs to get to temperature and hold it the downstairs just keeps on getting heat it doesn't need.

Matthew :

doesn't matter what size

Customer :

so what are you saying to do

Matthew :

okay here is what "I would do If it was my home"

Customer :

go ahead

Matthew :

I would install a 3 ton system on the 70,000 BTU furnace. I would then go in and power zone the system so that the upstairs and the basement both had a thermostat. These power zones close off the runs to the basement at the furnace if the basement doesn't not want heat or cooling and it closes off the runs to the upstairs if the upstairs doesn't want heat or cooling. This way I can control the environments separately and maintain the temperature I want within 1 degree on both levels.

Matthew :

If I didn't have the money for the extra 3,000.00 that power zoning costs i would put in the 90,000 BTU furnace on a 4 ton air conditioner.

Customer :

i dont have the extra for the power zoning so i guess i will have to do the 90 and tell the guy the 2 1/2 ton air is too small

Matthew :

and live with the basement being a little warm during the coldest days of the winter when the upstairs takes longer to heat up and a little colder during the summer on the hottest days when the upstairs runs longer to keep up.

Customer :

why does he think the 2/12 goes with the 90

Matthew :

Make sure you ask him to install a return run for the basement if they haven't already. If you do not zone the system this is the best thing you can do for the system.

Customer :

the 70 probably would not heat the basement and upstairs correct

Matthew :

90,000 BTU furance can handle up to 5 ton. You can put anything you want on it 5 ton and smaller

Matthew :

you just lower the blower speed down

Matthew :

It would heat it don't get to caught up in heating it up and cooling it down. It is about the time it takes to heat it up and cool it down.

Matthew :

efficiency

Customer :

what is the best efficiency

Matthew :

and for the difference in a 90,000 btuy and a 70,000 btu you may be talking 100 dollar a year difference in energy usage it's not that detrimental.

Customer :

thanks for being patient my husband dont check into this stuff we are 56 and this is the first time i bought a house he had a house when we got married so it is a new experience

Customer :

so your saying the 90 is the better one for this home

Matthew :

yes if you do not power zone it. Going bigger is better

Matthew :

If later on down the road you feel the system heats up too fast and it is too much BTU for the home you can always have them block one burners and decrease it.

Matthew :

If you go with the 70 and it turns out not to be enough for your liking there is nothing you can do about it

Customer :

matthew has been great and very gracious

Matthew :

Well thank you. Please tell that to the website when you leave feedback :)

Customer :

matt i have to say you have explained more to me than anyone i have talked with you have patience i went on earlier and i got some answers but you gave me the confidence i need to make a decision everything you said had a good explanation if i need to talk again will i get you or someone else

Matthew :

Again make sure you ask for a return run in the basement if there isn't one already. This at least will help circulate the air in the basement while the upstairs tries to satisfy the thermostat. If there is no return you will get hot dry air laying in the basement in heat and moist cold air laying around during cooling. With the return at least it circulates the air and pumps fresh in.

Customer :

this 2 stage furnance i guess it what makes the difference in btu huh

Matthew :

All 2 stage means is that it uses half of it's full BTU for a small amount of time and then kicks in the full BTU after that amount of time is up.

Matthew :

This is so if the thermostat drops 1 degree and the furnace kicks on it can try to heat the thermostat back that 1 degree without using the full gas usage. If after the 1st stage time is up which is normally around 4-6 mins then the full btu kicks in and gets it the rest of the way.

Matthew :

Just regulates the gas usage more than a single stage but you still are using the same amount of BTU furance

Customer :

i am getting that pure air system and also a lennox air exchanger not the big kind just one to bring more fresh air in that is what my husband and i did not undestand because the 90 starts at 66 btu and the 70 at 45 so he thought the 70 would run more.

Matthew :

the first stage starts at 45btu output and then ramps to 70 during 2nd stage. the 90 starts at 66 and ramps to 90

Customer :

and the one lennox guy said you will overpower it at 90 and if you get to big that is not good and the duct work cannot handle it

Matthew :

They both are going to run more than your old one that is just the nature of a 2 stage furnace. It is hard for people to understand this because you would think a furnace running longer means it cost more to run but it actually costs less because it's running longer using less gas.

Customer :

so you can see why people get confused with this stuff

Matthew :

This guy that said 90 was too much was he aware that the basement runs had been taken off the furnace?

Customer :

no the basement runs are on the furnance they go to other parts of the house you just have to open the vents in the basement but there are only 2

Customer :

i see what you are saying that the furnance is feeding the basement runs

Customer :

well we did not tell him we were going to use the basement for tv room etc

Matthew :

Even if you put the 70,000 btu in your home will heat and cool just fine really it will. It just may cost a little more per year then it would to get the same comfort with the 90,000 btu

Matthew :

and like I said why not go up so you have options if it is too big rather than go small and not have any option if it is too small.

Customer :

yeah your right just dont understand all this stufff one tells you one thing the other another thing better be safe than sorry if i have more questions how can i talk to you

Matthew :

Just come back to the thread it will still be here accept or not it will still be here.

Customer :

to the thread what does that mean

Matthew, HVAC Technician
Category: HVAC
Satisfied Customers: 2000
Experience: 14 years experience in the HVAC field of service, installation, Manual J & D calculations
Matthew and 10 other HVAC Specialists are ready to help you

JustAnswer in the News:

 
 
 
Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.
 
 
 

What Customers are Saying:

 
 
 
  • You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future. Jimmy Bagley, IA
< Last | Next >
  • You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future. Jimmy Bagley, IA
  • Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
  • This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
  • Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
  • Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
  • Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. Robin Elkton, Maryland
 
 
 

Meet The Experts:

 
 
 
  • gotoman for ac

    HVAC Technician

    Satisfied Customers:

    4657
    51 years of experience install design and repair of all makes and models of AC
< Last | Next >
  • http://ww2.justanswer.com/uploads/SE/ServiceTechRus/2012-6-7_2119_056.64x64.JPG gotoman for ac's Avatar

    gotoman for ac

    HVAC Technician

    Satisfied Customers:

    4657
    51 years of experience install design and repair of all makes and models of AC
  • http://ww2.justanswer.com/uploads/AL/alumalite/2012-5-10_234018_shutterstock506249951forJA500.64x64.jpg Phil's Avatar

    Phil

    Mechanical Engineer

    Satisfied Customers:

    3888
    Retired HVAC/ Electrical & Boiler contractor. Industrial
  • http://ww2.justanswer.com/uploads/skibum0101/2008-12-16_015819_just_answer.jpg Rick Mather's Avatar

    Rick Mather

    HVAC Technician

    Satisfied Customers:

    3132
    35 years experience, HVAC
  • http://ww2.justanswer.com/uploads/RY/Rygis20/2011-5-7_3143_DSC5324.64x64.JPG Matthew's Avatar

    Matthew

    HVAC Technician

    Satisfied Customers:

    1994
    14 years experience in the HVAC field of service, installation, Manual J & D calculations
  • http://ww2.justanswer.com/uploads/KE/kentguidry/2011-9-26_214316_0059.64x64.jpg Kenton Guidry's Avatar

    Kenton Guidry

    HVAC Technician

    Satisfied Customers:

    962
    12 years install/service experience.
  • http://ww2.justanswer.com/uploads/solarman1947/2009-12-13_223915_phpkKBcXq_c2PM.jpg Rick Ridley's Avatar

    Rick Ridley

    UK Heating Engineer

    Satisfied Customers:

    871
    Retired But have had 30 years on the tools, Ex CORGI
  • http://ww2.justanswer.com/uploads/Ironheadfan/2009-12-18_222416_pump_005.jpg Tom's Avatar

    Tom

    HVAC Technician

    Satisfied Customers:

    770
    16+yrs HVAC/R service. Residential Commerical Industrial
 
 
 
Chat Now With A HVAC Technician
Matthew
Matthew
Service tech
2000 Satisfied Customers
14 years experience in the HVAC field of service, installation, Manual J & D calculations