ReplyOn a 2 story house you either need an electronic zone system, manual damper zone system, or 2 seperate units to evenly heat/cool both levels.
Regular Guest
I have 2000 Sq feet home , I have original 30+ furnace that has 65K btu input and 49K btu output, and 2 Ton A/C., I had load calculation done and min BTU recommended for my home and size and the location is 70 K btu , was told this furnace is small for my house and the motor is not strong enough to push enough air up, the piping going to each rooms upstairs is 10in in diameter
issue I have with old furnace was not heating enough to upper floors and not cooling enough during summer I had to crank up heat or lower to cool down so enough get up stairs, I have set register in basement to try to push more heat/cool up but I am running to issues where those area are not properly regulated
so I have 3 contractors coming offering different option
1 contractor
offer to replace with the same size furnace 2 stage 70K btu
1 stage is 43k in / 41 out 2nd stage is 66k in and 62 out
2 ton A/C
2 contractor
offer 2 stage 90K btu 1stage 57in/55out 2stage 88in/84out
and 3 ton unit
3 contractor
offer 2 stage 110k BTu 1 stage 72in/70out and 2stage 110in/105out
and 4 ton unit
now I have dillema based on the load I had done which one I should go
each of them had their own reasons for choosing this unit and what is available on the market I am going with Ducane or Lennox depends by contractor offer
the first contractor dismissed the report and says I should choose identical unit size if I go higher BTU i might have issues and I got entire lesson but it would fill two pages, the second said that I will have two stage furnace if need more heat it will go to stage two and this is what he recommends
the third one said that going by the load calculation done on my house that the furnace will work much better it delivers the min but if more heat needed it will go to next stage if needed be .. looking for suggestions on this I thought it will be easier to made decision but my head spins , or should I try couple more
Professional Member*
On a 2 story house you either need an electronic zone system, manual damper zone system, or 2 seperate units to evenly heat/cool both levels.
Professional Member*
A larger unit will make a termpature inblance worse. You problem is undersized ductwork. No reason 49k BTU's could heat the whole house if you have evely dsitributed air. However, 2 story homes need zoning or 2 system to work well all year round.
You need a load calculation. The first contractor is correct, that going larger won't help, and I'm guessing your in a mild summer climate, so 2 tons may be plenty.
I bet a 60k BTU 2 stage Furnace and 2 ton AC on a zone sytem will probably work just fine. The two 10" ducts might be adequate if you can reduce the airflow going downstairs. A modulating zone system like Carrier Infinity might help too.
110k BTU is rediculous! I doubt you have large enough ductwork to handle. IT would be very noisy and extremely uneven temrpatures. LARGER FANS DO NOT PUSH AIR FURTHER. Air follows the path of least resistance and flow proportionally to the pressure created by the fan. So if lets say 30% of you ductwork by cross sectional area gose upstairs, then if the blower is moving 1000CFM, 300 CFM would go upstairs. If it's moving 2000CFM< then 600CFM will go upstairs. But if you have a furnace thaty's twice the size, it will run 1/2 as long. So if the downstairs theremostat swings from 68.5-69.5F and lets say 66-69F upstairs now, then if you doubled the size of the furnace, it would instead swing from 68-70F downstairs, and about 64.5-70.5F upstairs with the larger one.
Regular Guest
Originally Posted by motoguy128
thank you I think the first one will be best option..
Global Moderator
Most of the time throwing bigger equipment at a problem house just makes things worse. It's inefficient and noisy. Zoning can help, it can be a real problem if you are trying to stuff too much air into a too little duct and you really have a nightmare. Someone needs to take the time to do an accurate floor by floor or better yet, room by room load calc then decide if the ducting is up to snuff. I know of 2 homes WITH zoning that couldn't handle the upstairs. It doesn't do miracles though many think it does.
10" is 400 CFM or 1 ton. You use zoning to try to stuff 800-1200 CFM in there and it will howl. It will also short cycle the equipment on the zone panels overheat overcool protection if it has it or the furnace will cycle on limit for a short time til the limit fails or the A/C will freeze up.
Regular Guest
I have one more question
I have looked at this site http://www.acdirect.com/systemsize.php
and based on 2000 I am in zone 4 close to Zone 5 so 2000 sq ft x .45 = 90000 btu at 95% will be 85k btu
so if I go with 90kBTU furnace will this be overkill , I would like to install two furnaces but I don't have room and access to ducts to do it so have to rely on one, I am thinking that 70k is too small that max output is 62k btu
Professional Member*
Sounds like a balance issue, not insufficient duct issue.piping going to each rooms upstairs is 10in
You want to go from 49k (that's served the house for 30 years) to 62k, and worry that is UNDERSIZED?I am thinking that 70k is too small that max output is 62k btu
Does your 49k furnace ever run continuously and not satisfy the house? Or does it shut off and not satisfy the 2nd floor?
A furnace that shuts off is not undersized. It is likely oversized. If it shuts off it means the thermostat is satisfied. Putting in a bigger furnace only makes that happen faster, which means those far runs getting little heat now (because all the heat is lost heating up long, cold ductwork) will get NONE.
Regular Guest
I have played around with registers to try push more air upstairs
right now I have set thermostat to 72, upstairs 2nd floor is 62
thermostat is in main hallway no registers are located nearby
it runs then when thermostat is satisfied is shuts down while air cools faster upstairs than on main level
I had done load calc 5 years ago by the one the energy and I was told we needed min 70k btu to heat the home , and recommended 2.5 to 3 ton ac
issue I have now that we dont have any trees we are exposed to wind and heat during summer and now it feels like I am loosing heat quicker I have to push the heat up to keep me comfortable and this has been like that from the time we lived here, during summer I had to bring thermostat really low to cool down the home, ..
I don't want to make that mistake I have done in previous home were we did what contract replaced with the same furnace output and a/c and run to the same issue where furnace had to run for hours to heat and during summer to cool down the home, our neighbor had over-sized a/c and furnace on 900 sq feet she had 3 ton a.c and 80k btu, we had 1.5 ton a/c and 40k btu furnace
I am very confused there is no uniformity in information everyone has different opinions every site has different info
I want to be comfortable
Professional Member*
Sounds like the house may have some big leaks. If the house is deficient, that's not the equipment's fault. If you attempting to heat the outdoors you are destined for failure. (Have you had a leakage test?)air cools faster upstairs
Also, part of your confusion is you want the equipment to not run. You will accomplish shorter run times with bigger equipment, but you won't like the noise, comfort, energy or maintenance costs.
Unfortunately, whether your home is gaining or losing heat whether the equipment is running or not. The shorter your equipment runs, the worse things get. The solution is equipment that never shuts off, not equipment that never runs.
Think about a milk jug with holes in the bottom that you want to keep 1/2 full. It's under your kitchen faucet. What is the best way to keep it 1/2 full?
Will you blast it every time it dips below the 1/2 line, and shut off every time it goes above? Or will you adjust the faucet so it matches the water lost out the holes? Which is easier? Which uses more water?
With your home, every time your equipment shuts, the duct cools. How much duct is there too upstairs? How much to downstairs? The same? How long does it run? 20 minutes or 2?when thermostat is satisfied is shuts down
When the furnace comes on it blows cold for a short time, right? Very quickly hot air is delivered to the areas closest to the furnace, right? Not so for the far runs. Cold air is delivered to the far upstairs rooms for much longer than downstairs. If the furnace satisfies downstairs before the duct warms up, only cold air was delivered upstairs. Is it confusing why the upstairs is cold?
Equipment that delivers less intense heat will take longer to satisfy the thermostat. Ducts will get evenly warm, and deliver evenly warm air to all rooms, and the rooms will be much more even in temperatures.I want to be comfortable
Equipment that shuts off is oversized to the load. If your equipment always shuts off, it's always oversized.
Regular Guest
Ok I am start to grasp what you are trying to say,
it is better to let the furnace run longer to heat up home so I should go with contractor 1 as best option for my house
the ducts are the same throughout home they are 10" connected to main distribution ,
there are 6 ducts running upstairs , and downstairs there are 5 of them , and 3 in basement
Professional Member*
Sounds like your main problem is that your upstairs is losing its heat too fast in the winter and gaining heat too fast in the summer. I think a home energy audit would serve you well. Lots of the problems it uncovers can be solved by a homeowner a few tubes of calk and some insulation. www.comfortinstitute.org www.bpi.org
Professional Member*
It will continue to become more clear as you let it sink in. Here's another nudge:
You don't want to heat UP your house, you want to HEAT it. In fact, what you want to do is REPLACE JUST THE HEAT LOST. Any more is overheating.
Furnace efficiency is impacted by a lot of factors. A lot of inefficiency when equipment is warming up. A lot of wear and tear too. Some equipment is rated in cycles, not run time.
So you want your equipment to run continuous, you get the best comfort AND the best efficiency. City stop and go v/s highway at 45mph. (My car goes from 22 mpg >5 miles to 55mpg at 45 >20 miles.)
Regular Guest
I had energy done 5 years ago, one of the issues was not enough insulation in the attic was only 6 inches which I fix that by adding another 12 inches, I had brand new windows put inside before the audit, and added spray foam between the studs and windows so they were insulated
next issue my outside walls from the ground to half was covered with brick from half to top of the roof was covered with metal siding , and under that siding and brick there was no house wrap there was a 3/4 paper board behind that is 2x4 with bat insulation and inside they put thin sheet of clear foil not the thicker the cheapest stuff which is not air tight , the brick add some insulation but the upstairs is not well insulated and option was to replace siding and home wrap the upper part add the foam insulation for exterior and put new siding on the top of that
Professional Member*
Did you have a blower door test done? Finding your CFM50 leakage number would be really worthwhile.
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