New House, Bad Furnace Size (Need help)

[meter1]

I just bought a new house this summer in Texas. Now that it has gotten cold I noticed that the furnace is just not getting the job done downstairs (it runs constantly and doesn't heat quickly). My first thought was that the unit was not sized properly.

I contacted the people that installed the furnace several times. First they checked to make sure all the burners were working. Then, they sent an air balance crew and they didn't do anything because there wasn't enough output. Then, they sent a crew out to do so duct work and added an additional return. After all of this work was completed the unit still is not heating properly down stairs.

They finally broke down yesterday and agreed to replace the unit. The unit that they had was 60,000 BTU and they are going to replace it with a 80,000 BTU. I know that increasing the size will help. But is this the proper size for my home? I have about 2100 sq feet down stairs with 10 ft ceilings throughout. The master bedroom has 12 ft ceilings and the family room is open all the way to the 2nd floor ceiling. The total square footage of the house is 3300.

Also, since they put the wrong size unit in don't they have to compensate me on my gas bill since it is running constantly due to the furnace's inefficiency compared to the size of the house?

Sorry for the long message, any help is appreciated.

Thanks!

[Edited by meter1 on 12-15-2005 at 01:49 PM]

[BaldLoonie]

Smaller furnace won't cause bigger gas bill, maybe smaller since it isn't keeping up.

Demand a heat loss study so you can see that the 80K is the right size.

[meter1]

It seems to me that the gas bill would be higher since the unit is running almost non-stop throughout the night. I would think that a properly sized unit that pulses on and off correctly would generate a smaller gas bill.

I was trying to get an opinion on sizing before they come and replace the 60k unit. What is a heat loss study and can it be done before they install the new unit?

[meter1]

I have another question as well. They put the upstairs thermostat in a bedroom. Is this common practice? They said that they put it in the bedroom because it gets hotter in the upstairs hallway and the bedroom is a better location. But if someone is staying in the bedroom I will have limited access to the thermostat. I just want to make sure I am not being fooled.

[pecmsg]

Originally posted by BaldLoonie
Smaller furnace won't cause bigger gas bill, maybe smaller since it isn't keeping up.

Demand a heat loss study so you can see that the 80K is the right size.

Agreed. Do your own heat loss (Red tab above) I would also question the duct work if there going to increase the furnace size. It may or may not be able to handle the increased CFM’s.

[Wild Leg]

A furnace is like a car.

Long run times = Highway miles per gallon.

Short run times = City miles per gallon.

A furnace is only efficient after it warms up, just like a car.

An oversized furnace will have too many warmups.

Yes, a heat loss survey can and should be done before installing the new furnace.

[mayguy]

Where are your returns?

your supply vents? What style of vent?

the 60 could be enough for your home. just poor ductwork or vent set up.

[JoeSix]

Originally posted by meter1
I just bought a new house this summer in Texas. Now that it has gotten cold I noticed that the furnace is just not getting the job done downstairs (it runs constantly and doesn't heat quickly). My first thought was that the unit was not sized properly.

You haven't mentioned anything that is "wrong" yet. A properly sized furnace will (1) run almost constantly in cold weather and (2) won't have a great deal of pull-up capability.

If it maintains the temperature at the design outdoor temperature (whatever it is for your area), then it could very well be the right size. Are you setting the thermostat way back at night?

Long running times don't necessarily mean more cost, and can mean the opposite. It takes a while for the furnace to reach it's rated efficiency, and one that starts and stops all the time is less efficient than one that purrs along at a lower speed, so to speak.

Look at it this way, the 80K furnace will put out 33% more heat while burning 33% more fuel than the 60K furnace running the same amount of time, and will run about 25% less time to put the same heat in your house. So, if the 80K furnace runs for 45 minutes each hour (say 15 minutes on, then 5 off), while the 60K furnace runs continuously for the same hour, in theory the same amount of gas would be used if each was running at the rated efficiency. However the 80K furnace is cycling, and is less efficient for the first 5 minutes or so of the cycle. The bigger furnace is also going to be louder with higher air flow at the registers.

The real key is whether or not you can be comfortable, not how fast the system heats the house or whether it runs a long time. A cycling system produces temperature swings and doesn't mix the air as well, allowing cold spots to develop while its not running.

[meter1]

The returns for the unit in question are downstairs in the master bedroom, hallway outside master bedroom, hallway outside bathroom, and dining room. An extra one was added to upstairs. The vents are adjustable where you can angle them and the contractor adjusted them.

The problem is that the house is not heating when I get home. I get home around 6 or so and the unit never reaches 74 degrees and I usually go to sleep around 12. I leave it on 70 while I am way and when I sleep. It is always cold downstairs and it doesn’t feel like enough heat is being generated.

Can someone talk about the thermostat question that I asked?

Thanks.

[amd]

74 F is a very high heating temperature - most people keep it at 67-70 degrees. Perhaps nothing is wrong, given that the design temperature could be below your setpoint.

Consider adding a humidifier to feel warmer at a lower temperature.

Don't refer to the thermostat reading; if you're comfortable, that's all that matters.

[dan sw fl]

[QUOTE]Originally posted by meter1
[B] They finally broke down yesterday and agreed to replace the unit. The unit that they had was 60,000 BTU and they are going to replace it with a 80,000 BTU. I know that increasing the size will help. But is this the proper size for my home?

I have about 2,100 sq feet down stairs with 10 ft ceilings throughout. The master bedroom has 12 ft ceilings and the family room is open all the way to the 2nd floor ceiling. The total square footage of the house is 3300.

[Edited by dan sw fl on 12-15-2005 at 08:33 PM]

[arc8]

Wow!
It's Cold up here, around 10 degrees. The furnace can heat the house to eighty, just give it some time.

Here's a two thoughts: 1. A new 3000 sq ft house up here has a 60,000 btu 92% gas forced air furnace. It heats the house fine and more than 72 degrees.

2. Here's a another house, 3000 sq ft, fourty years older. It has a 100,000 btu 80% gas forced air furnace. This one has a hard time keeping up and struggles to heat over 73 degrees.

Question: Why is that? only one answer is needed. I believe the problem with meterman's is this one. A very common problem indeed.

[JoeSix]

Originally posted by meter1
I have about 2100 sq feet down stairs with 10 ft ceilings throughout. The master bedroom has 12 ft ceilings and the family room is open all the way to the 2nd floor ceiling. The total square footage of the house is 3300.

Wow. I read this again and have a question: You're heating that entire house with a 60K furnace? I thought you were just talking about the downstairs.

I also have a two story family room. It's going to be trouble to heat unless it's zoned. It needs a lot of air flow in the winter to be warm, and then not much in the summer to keep cool, and any non-zoned flow to that room will likely be too much for the summer and not enough for the winter. Do you find the other rooms downstairs are warm enough, just not the family room? If so, it's just that two-story spaces are easy to keep cool but hard to keep warm. An unvented gas log set would help much if you have a fireplace, but those don't look as good as a real fire or vented set.