Regular Guest
Hello,
I have a slight concern and would think this forum can answer my question since you all have a lot of experience with furnaces.
My question is what size of furnace is required for a 1100 sq ft house with R12 walls (basement and upper level) and R40 in Attic it is a bungalow and the basement is completely finish with heating.
Heating main level and basement, basement have cold air return vents and all rooms in main level.
I am in the process of selecting a GMVC95 - 0704
Hi-fire output: 67k Btu
Lo-fire output: 47k Btu.
This is a multi-position, two-stage, Variable speed gas furnace.
What do you think?
Any help, comments would be appreciated.
richard
Regular Guest
You need a Manual J heat loss calculation to determine the best size for your house. Most likely a 95% 70k BTUH is oversized for your house.Originally Posted by netminder
The smaller GMVC95045 would probably do it but you need the calculation to know.
Professional Member*
I would suspect grossly oversized!
Regular Guest
You're probably right. I have a tendency for understatement at times.
Professional Member*
Where do you live as that affects the load on the house.
.
The statement below is my signature and just my overall feeling towards our industry and does not necessarily pertain to you nor this thread.
There really isn't a legitimate excuse for not doing the job correctly!
Regular Guest
I live in Winnipeg gets pretty cold in the winter -29 deg C to -36 deg C.
I keep temperature around 20 deg C at home
Regular Guest
It could be worse. You could be in Yellowknife or Whitehorse.
Professional Member*
All houses are different and to know for sure, someone needs to do a load calc on your house to tell you what size you need...other wise it is all a guess and ball park.
.
The statement below is my signature and just my overall feeling towards our industry and does not necessarily pertain to you nor this thread.
There really isn't a legitimate excuse for not doing the job correctly!
Regular Guest
Seriuosly netminder - if you want good comfort you need to get someone to do the calculation, or with a little effort you can do it yourself for $49.
http://www.hvaccomputer.com/
Regular Guest
thank you garya505 for that link I will try that and see what I get. But just as an estimate if anyone lives in the same temperature and approximate square footage of house I am curious what is their furnace size. I know insulation values and windows etc affects but just looking for a ball park.
Regular Guest
O.k I had a tech come in and said that around this area 46~70btu is what everyone has due to the cold temps but he did say that the furnace blower maybe set to high.
It cycles on low at start up (temp around 65deg-f) and then kicks in to high till it reaches the temperature of 70deg-f, then switches to low then shuts off (this takes about 15 min). Stays off for 7 min then back on again but on low this time for another 7 min this continues through out the whole day.
What do you think is causing this or is this normal??
Professional Member*
sounds like you need to find where your heat is escaping
Regular Guest
Your indoor temperature is going between 65F and 70F? Is that what you want? Is your thermostat controlling that?
Regular Guest
No the temperature don't change from 65 to 70 and back to 65 again.
What I meant is if the current temperature in the house is 65 and I set the furnace to 70 then it starts on low for a minute then goes to high (like a hurricane blower very powerful) for 15 min then shuts off.
It will start back again in 5~7min to main the 70 but it only lasts for 7 min then shuts off again. I am not sure if this is normal but I would except the furnace to stay on all the time instead of cycling. Don't get me wrong I get enough heat in the house just worried about what effect the cycling is having on the house and furnace.
Thanks for you replies, but I know you all have come across this before just wanted some clarifications.
Regular Guest
The furnace is always going to cycle, and would only run all the time if it was really cold outside. Sounds like you are getting 5 cycles per hour, which is a common setting for thermostats.
Professional Member*
netminder
how many cycles/hr do you get?
one cycle is defined as a run time and an off time for average winter low temp.
post back.
God Speed, Jim. We'll miss you - 2-26-23
What is the temp outside when it does this kind of cycling.
Regular Guest
I am going today and check how much cycles I am getting per hour, I will also give check the outside temperature and post the results later on.
In the mean time I have another question I am pondering, if the blower fan is to powerful can it harm the house? How can a house become over pressurized? My blower fan goes on like a hurricane blowing my curtains all over the place, I don't mind the noise except that it is powerful.
Is there a problem with this.
Professional Member*
netminder
if your new furnace is sized correctly, you have adequate ductwork both supply and return, blower motor is VS and settings are correct, then blower motor should barely be heard if at all.
IMO
Professional Member*
gmvc 70 drops to 45, so if sized correctly you should get nice long run times with a properly set up 2 stage stat, or better yet the communicating stat. That seems a lot of furnace for 1100 sf, even in the great white north.
As you can see, airflow noise complaints raise antennas here. Hopefully your ductwork can efficiently handle the airflow needed for a 70. If not, tightening the house and getting a smaller furnace will really pay over replacing ductwork.
A thorough audit should tell your current load and determine if there are opportunities to tighten up and downsize your furnace. IMO, you REALLY need a blower door test number with temperatures that cold for an accurate load calc. Goodman might not be the ideal brand if you can't get your load to 45 as that house may straddle the range between the sizes. Others, (like carrier) will have broader output range (mvc060 = 22k through 58k)
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