Getting the Most From a High Efficiency Furnace

 Lennox G71 MPP 95% Efficient Furnace

    

     If you've ever shopped around for a new or replacement furnace for your home, you know how confusing it can be. After all, how many times during your life do you replace your furnace? Once? Twice, maybe? Gone are the days of 50% efficient furnaces when half of the energy consumed by the furnace heated your home and the other half heated the great outdoors. Also gone are the days that you could replace your furnace for under $2,000.

     For today's technology, with furnaces reaching nearly 98% efficiency, replacing your furnace can cost upwards of $7,000. If you're spending that amount of money, shouldn't you make sure that you're getting the efficiency that you paid for? Of course. So here are some tips to ensure that your furnace investment does what you want it to.

A Lennox G61V high-efficient
furnace. Notice the two white
plastic pipes on the right
hand side of the furnace - the
intake and the exhaust.

 Tip#1

    Ensure that you get a 2-pipe system. By this I am referring to the vent pipes attached to the new furnace. One pipe is for the exhaust, the other is for air used by the furnace for the combustion process. With a two pipe system, the furnace draws cold, unheated air from the outside to burn with the gas then exhausts the waste products back outside through the second pipe. With a one pipe system, the air used by the furnace for combustion is drawn in from your home - that's air that you have already paid to heat.

     Remember, the efficiency rating of your furnace only refers to the efficiency of the internal operation of the furnace itself, and not to the overall efficiency of heating your home. You're wasting a lot of heat and money without having the second pipe. A 92% high-efficiency furnace with only one pipe can cost you nearly as much in energy costs as a mid-efficient furnace.

Tip #2

     Do not over-size your furnace. Bigger is not better. In fact, it can be worse when it comes to efficiency. If a furnace has excessive much heating capacity it can heat the home too quickly thereby never running long enough to reach its proper operating temperature. Think of this in terms of how your car operates before the engine is fully warmed up on a cold morning.

     Many times we have seen installers sell the highest profit furnace instead of the most suitable one. Here is a rough formula that you can use yourself. Every furnace has a rating plate on it stating the BTU input. If, for example, your furnace's rating is 80,000 BTU and has an efficiency of 50%, then the heat input into your home is 50% of the 80,000 BTU's, or 40,000 BTU's. If the new furnace you are considering is 95% efficient and has an input rating of 50,000 BTU's, then the 50,000 BTU input results in 47,500 BTU's of heat input into your home (50,000 x 0.95). That's comparable to the old, 80,000 BTU furnace.

     This is a rough guide only as it does not take into consideration other home upgrades such as new windows, added insulation or draft proofing having been done that will reduce your heat loss and lower the required furnace output.

     If you are being offered a furnace that does not have a BTU output calculation that is relatively close to the BTU output numbers of your current furnace, make sure that you get a logical answer as to why. Sometimes there are valid reasons for this and a qualified heating mechanic will be able to explain his reasoning.

Maximizing the Efficiency of Your Air Conditioner

    

     One of the most common mistakes made when installing a central air conditioner is assuming that the higher the SEER, or Seasonal Energy Efficiency Ratio (this is the effeciency rating posted on the outdoor condensor unit), the higher the efficiency of the system. Not so fast. Yes, the higher the efficiency of the air conditioner condensor the better, however a factor of primary importance is the evaporator coil (indoor coil). Evaporator coils have huge efficiency differences between them, and the true SEER of your air conditioning system needs to be calculated in terms of the system as a whole. The outdoor unit is only one piece in the system.

Consider the following performance measurements.

     A Lennox 14 SEER air conditioner condensor combined with a C33-48+ evaporator coil operates at a combined system efficiency of 13.0 SEER. Yet that same Lennox 14 SEER air conditioner condensor combined with a C(A,C,D,E)36C34+ evaporator coil operates at 13.5 SEER. Again, that same 14 SEER unit will only reach 14 SEER with a A(A,B)W364+ evaporator coil or something similar. SEER ratings as high as 14.5 and 15.0 can be achieved if this air conditioner condensor is used in combination with a variable speed DC blower motor.

     This variation in real efficiency holds true throughout all makes, models and brands. The Lennox 14 SEER was used solely for illustrative purposes - I could have chosen any unit from Carrier, Amana, York, etc., and had the same differences in efficiency. The effects on efficiency due to coil type are even more pronounced in heat pump systems than on air conditioners.

     So why would an air conditioning installer use a lower efficiency coil? There are a few factors, the main one of which is that the higher the rating of the evaporator coil, the larger its physical size. A bulkier unit can be more cumbersome to install and is often not used because of this reason.

     If you're considering installing a new air conditioning system or replacing an old one, ask for a high-efficiency coil. They only cost about $45.00 to $100.00 more and you'll save your money back within the first few months.

TXV

     Two other ways to increase the SEER of your air conditioning system are to have a TXV and TDR installed. A TXV, or thermostatic expansion valve, modulates the flow of refrigerant gas inside the cooling system. A TDR, or time delay relay, controls the timing of the indoor blower fan to maximize cooling and efficiency. Many manufacturers build TDRs into their furnaces, while good quality thermostats also have them included. Just make sure that your a/c installer sets them properly.

XP17 Heat Pump Video

     This Lennox XP17-036 heat pump is a solar powered unit. You can hear how quiet it is in this informal video by comparing the unit's noise level to that of the birds chirping in the trees or to the fence gate creaking in the background. It is running at full capacity cooling a home of approximately 3500 square feet. Other models can heat or cool up to 5000 square feet per unit.

     We had installed a 4 ton unit in another nearby home and it was equally as quiet. The owner was expecting to hear a certain noise level from her unit and asked "When is that big boy going to turn on?"  I wish I had a video of her face when we told her that it was already running.

Solar Powered Heat Pumps and Air Conditioners

New for 2010, Lennox has begun to release their new solar powered heat pump and air conditioner product lineup. Referred to as "SunSource Solar Ready" units, these new heating and cooling units come with built-in controls and electronics to allow the home owner to attach anywhere from 1 to 15 solar power collectors, though it is not necessary to use solar power to run these SunSource units as they are also able to use your home's electrical supply just like all other heat pumps and air conditioners do.

In southern areas, with good south-facing exposure, the solar panels can collect almost 300% more power than is required to operate the a/c or heat pump. Through the addition of the iComfort controller / thermostat, the excess power collected can be fed back into your home's electrical system. Excess power can even be sold back to your electrical utility's grid (if offered in your local area).

SunSource Solar Powered HVAC System

Consider the green environmental impact is we were to remove the entire air conditioning load from the existing power grid. A few less brown-outs would be appreciated too.

Current models available are the XP21 Heat Pump, the XP17 Heat Pump and the XC17 Air Conditioner.