When homeowners are planning a furnace substitute buy, there are a few simple questions that you need to be prepared to answer in order to get the correct furnace for your application.
1. What Efficiency do I want or need? (80%, 93% or 95%)
2. How will I vent the unit (vent pipe or PVC)
3. Direction of Air Flow (Up, Down or Horizontal)
- The basic three obtainable choices on the market today are 80%, 93%, and 95%. It seems like a no brainer to choose the highest efficiency unit. It would seem so, but the reality is that you have some choices to make here.
- traditional 80% gas furnaces are vented with uniform metal vent pipe flues and often require exit by roofing. The 80% furnace is the lowest price point in the furnace market, but with that price point comes trade-offs. First and foremost is efficiency. An 80% efficient furnace is just that, 80%. That method that 20% of every dollar of fuel that you use to heat your home is lost by burned exhaust gases.
- The 93% gas furnace has become the popular furnace of choice for most homeowners. One of the most attractive features of the base level high efficiency furnace is its venting flexibility. The 93% furnaces are called “Condensing Gas Furnaces”. Most have dominant and secondary heat exchangers, which add to the efficiency and allow these units to be vented with standard plumbing kind PVC plastic pipe, and can be vented in a variety of configurations, including the ability to exit a sidewall or basement foundation and vent directly out in a horizontal run. This flexibility in not having to penetrate roofing materials is a great advancement. The other noted advantage of the 93% efficient gas furnace is the increased savings that are achieved. A 93% furnace is about 14% more efficient then the standard 80% version. This can equate to meaningful savings and already though the 93% high efficiency furnace is on average about 40% more expensive then the 80% models, the realized savings can easily make up the difference over a short period of time.
- The ultimate choice come in the 95% and up form gas furnaces that by description, appear to only be slightly more efficient then their 93% style, but at closer look you will find that this group of furnaces is in a class all by their selves. The ultra-high efficient 95% gas furnaces often are combined with variable speed blower drives, two -stage gas valves and a large number of other additions that not only make these furnaces more efficient, but more comfortable along with generally being near silent in their operation. Along with the 2% increased base gas efficiency, two-stage gas operations allow the unit to fun and fire at a considerably reduce rate during marginal outdoor temperatures. This adds to the saving on energy bills. The variable speed blower drives not only add to comfort and efficiency of operation, but since they are programmed to “ramp up” and “ramp down” during run cycles the normal air flow that you hear with traditional venting systems is greatly reduced. It is not uncommon for homeowners to never hear theses unit run. These extended run cycles and variable air flow also adds to the efficiency of air conditional systems that are operated in combination with these furnaces. The price point of these optimum 95% furnaces can be 30%-40% more then the 93% single stage versions, but the additional comfort and efficiency benefits need to be considered.
- As mentioned above, there are multiple options for venting your gas furnace and knowing what you want and or need is an integral piece of the furnace choice.
- Metal or PVC? This choice is determined by the efficiency of the furnace that you choose and or the limitations that you have with your building structure. As stated above, 80% gas furnaces utilize uniform sheet metal vent pipe and are typically vented by roof penetrations. In some situations, you may already have a vent that you want to utilize and your furnace choice could be dictated by that venting material. The furnaces that classified and rated at 90% and above typically utilize PVC pipe to exhaust the burned gases. The PVC vented furnaces offer greater flexibility when venting, as in addition to roof penetrated venting, these furnaces can also be vented in horizontal directions, by sidewalls and basement foundations.
Direction of Air Flow:
- This last piece of the furnace choice question is basic when choosing your furnace. Here are some guidelines to help you decide.
- Upflow – This kind of configuration is often found in basement locations. The return or intake air of the upflow furnace will go into from the bottom and the supply air will flow out of the top of the furnace and then be directed to duct and vents above. This configuration can also be found on the same lave as the living space and then vented upwards and into ceiling registers or floor registers in upstairs rooms.
- Downflow or Counterflow – This kind of furnace is exactly as it sounds in comparison to the upflow models. Return air or intake are is brought in by the top of the furnace and flow out the bottom. This kind of furnace is often in main living areas and feeds vents in floor in addition as ceiling vents in lower levels. They can also be used in attic setting where a downflow scenario is needed.
- Horizontal – Often, the above mentioned upflow and downflow furnaces can also be configured in a horizontal position. To visualize this, think of the furnace laying on its side. Instead of up or down, this configuration allow are to be drawn into one end and depleted out the other horizontally. This can be useful in attics that have very little height to adjust to a standing furnace. They are also used in basements or root cellars that have lower then average ceiling heights that are unable to utilize the upright furnace.
If the choices above seem confusing, talk to your home heating and air conditioning expert before you buy your next system. Most HVAC stores online have phone numbers to call or live help agents to help you make the right choices for your home.