Gas and Oil Home Heating Furnaces - Need Help- High Efficiency Gas/ Hot Air Furnance

Would appreciate assistance with the following do it yourself project:

Project Replacing 30 year old gas fired upflow hot air furnace with new high efficiency unit. Want high efficiency unit so that I can remove chimney which goes up kitchen wall; want additional space for future kitchen remodeling.

Current furnace GE unit Input 120,000 BTU. House dimensions:
(split level) Partial Basement: 520 sq. ft.; 1st floor 700 sq. ft.; 2nd floor 600 sq. ft.; 3rd floor 675 sq. ft. Do not want to go cheap but cannot afford the Mercedes or Cadillac of the industry. Want quiet operation.

Questions:
What size unit do I need?
90%; 92%; 94% efficiency?
Single or 2 stage operation? What is the difference?
Variable speed seems very expensive. Is it worth it?
What brand is perferable? Heil, Comfortmaker, Amana, etc.
Any particular model you would recommend?

Thanks,

1) Someone needs to do a Manual J heat loss calculation to properly size the heater.
2) All of the 90+ heaters extract heat out of the flue gasses so that acidic water is condensed and must be disposed of somewhere. The efficiency differences are minor. Depending on your climate and heating needs that type of efficiency might not be economically justifiable. In the sun belt, go with an 80% furnace.
3) 2-speed will deliver greater comfort and efficiency than a 1-speed with the same efficiency rating.
4) Variable speed is even better than 2 speed but costly. If you have allergies and want to filter the air continuously, Variable speed is the ONLY way to go. It will save hundreds of dollars every year on continuous fan operation.
5) Nobody makes a BAD machine. Some are somewhat better but the sizing and installing of the equipment matters far more than the brand. Focus on the dealer not the equipment.
6) No. A bad dealer can spoil the best equipment.

Units are very seldom undersized. OVERsizing is the rule. Comparison to other homes will be misleading.
You can have the calculations done by a local contractor as a part of the bidding process. Request the calculations to be done in writing and ask for Manual J conformity. Expect to pay for this service.

You can also go to the web. One location is:
http://www.comfort-calc.com/price.html
Download their forms and you will get an answer. The best calculations conform to Manual J by Air Conditioning Contractors of America (ACCA). Ask them about the basis for their calculations.

Yes...bigger than needed boilers, heaters and air conditioners all waste enormous amounts of energy and money. But the sellers like to sell them because it makes life easier for them. Most companies will likely rush to sell you much larger equipment and Profit from your situation without even doing a proper heat load calculation.

Hey,
You want atleast 50 btu's for every sq foot of your home and in your case.You have 2495 sq ft x 50btu's =124,750 btu's
124750 / 12000 btu's =10.3958. So you need a 10 and 1/4 ton unit but I don't know if they sell them in 1/4 ton sizes,so you'll probably have to go with a 10 and 1/2 ton unit.To help you understand my math 12,ooo btu's equal a one ton unit.As far as systems or particular styles go I prefer a Trane to any other.I myself have seen alot of undersizing when it comes to newer homes,informing the customer that they can save money buy purchasing a certain unit,not letting them know that that very same unit will not adequately cool nor heat their home.Like above you want 50 btu's for every sq ft for heating and 12,000 btu's for every 400 sq ft for cooling and remember a heat pump is sized for cooling not heating.Hope this helps.as far as efficiency is concerned you can get a really high seer rating,seasonal energy efficiency rating,some go up to like 19.Remember though, more efficiency,more parts,more things that can go wrong,more things to pay to get fixed.

You can see what other authorities have to say on equipment sizing:

See "Bigger is Not Better" at: http://www.proctoreng.com/articles/bigger.html for an excellent look at sizing air conditioners.

Anther view of proper sizing is at; http://www.buildingscience.com/501c.PDF
They find that even 80% of Manual J sizing is very adequate in Tucson, AZ.

Also see: http://www.eren.doe.gov/consumerinfo/refbriefs/cb7.html

Quote: "Sizing Heaters and Air Conditioners: Quick but Inaccurate Methods

The following are some of the "quickie" methods some contractors may use to size a system. They are also somewhat useful for very rough sizing. NEVER use any of these to determine the final size.

The contractor walks in the house, looks at the existing unit, and recommends that the replacement unit be the same size, or larger. This obviously does not take into account any improvements made to the house or mistakes made in sizing the original unit.


The contractor asks you how many square feet of living space there are in your house, then tells you what size unit you need. This is called "sizing by square footage" and is the most commonly used inaccurate method of sizing. A typical value used for air conditioners is one ton (12,000 Btu/hour) per 500 square feet (46 m2). This does not take into account differences among house orientation, insulation levels, design, construction, and energy efficiency or intended use of the system. You may get different answers from different contractors who use this technique. In that case, they may have a different "rule of thumb," or one of them may be using the "lowest cost" method. This involves adjusting the square footage rule so that whatever the contractor has in their warehouse becomes the right size for you. Since the "in-stock" unit costs the contractor (but not necessarily you) less to install, this becomes the "lowest cost" method."



The following is advice from “Consumers Report” 1998…Quote:

"Choosing a contractor
A successful central-cooling purchase depends most of all on finding a contractor who will size and install the equipment correctly and will charge a reasonable fee. "