We already have a 2 speed 18seer unit and it works VERY well. Variable speed blowers were not yet mainstream when the unit was purchased. The furnace blower has 5 different speeds, 3 of which are used. 2 for the 2 stages of cooling, and a lower one for the furnace. I realize a bit of efficiency is lost over a variable speed blower but without an inverter driven variable speed compressor, there is not much advantage to the variable speed blower. They use fixed speed setpoints anyway for the two speed condensers. My question was with regard to configuring the system as a hybrid heat pump with gas furnace instead of straigh AC with gas furnace. Can anyone answer this? Most hybrid systems place the cooling coil upstream of the furnace heat exchanger so that both heat sources can be used at the same time, in my arrangement, it would have to be either gas or hp, never both. Is it worth the $200 difference in cost or is there something else I am overlooking?

I live in Harford County in an all-electric home. The cost of running a heat pump in the winter varies with the outside temperature. As outdoor temps drop, the btu's produced from the heat pump drops, and the C.O.P. (coefficient of performance) also drops. COP is the efficiency of the heat pump. At 32F outside, a typical heat pump has a COP of 3. Cost of 1 million btus at 13.5 cents per kw-hr, COP = 3: (1,000,000 btu / 3413 btu per kw-hr) x $.135 / 3 = $13.18. So the cost of 111 million btu = $13.18 x 111 = $1464. Don't be fooled by SEER. 44% of the value of the SEER calc is at 67 and 72F outdoor temps. I don't run my a/c at these outdoor temps. EER determines your true cooling costs. Whichever SEER system you get, you want 12 EER and 9 HSPF minimum. Also, because you are looking at a heat pump, you want full btus at the 47F rating temperature. Anotherwords, a 3-ton system should be 36,000 btu, not 33,000. Some condenser/coil combos are weak on heating btu's. The Trane XL16i is notorious for weak heating btu's. Good luck.

I was trying to gauge the cost(for natural gas) when my furnace has run(consumed gas) for an hour's time. I did it two ways. First I just took the BTU input rating of the furnace and did the calculations from there. Then someone pointed out that the BTU input rating may not be an actual value. So secondly I needed to determine the amount of gas my furnace is actually consuming per hour. Here are the particlars: 1. I have Goodman model GMPN100-4 furnace. (natural gas, single stage, pilotless and an input rating of 100,000 BTU per Hour) FIRST WAY USING BTU INPUT RATING: 1.One cubic foot of natural gas has about 1,030 BTU. 2.Divide the furnace input rating(in my case 100,000) by 1030 to get the number of cubic feet of gas the furnace will use in one hour. So 100,000(BTU) divided by 1030(BTU per Cubic Foot) is about 97 Cub Feet. 3.My supplier's bill is based on units of one hundred cubic feet(CCF) so I divide 97 cubic feet by 100 to determine how many CCF the furnace will burn per hour. This turns out to be 0.97 CCF 4.My supplier charges $.745 per CCF so it costs me 0.97 times $.745 = $.72 per hour for natural gas for my furnace to run. SECOND WAY BY DETERMINING ACTUAL GAS CONSUMPTION: As stated above someone pointed out that the BTU input rating may not be an actual value. So I wanted to determine how much gas the furnace was consuming per hour. My gas meter has a 2 cubic foot dial. I set a video cam in front of the gas meter in the morning knowing the furnace would be on for at least 20 minutes to bring the house up to temperature from the night's setback. The furnace did run for about 20 minutes but I stopped my readings at 10 minutes. Here are some findings: In 5 minutes the furnace consumed 7.6 cubic feet of gas. In 10 minutes the furnace consumed 15.2 cubic feet of gas. So 15.2 cubic feet of gas in 10 minutes extrapolated out to 60 minutes would be 91.2 cubic feet gas per hour or 0.912 CCF/hr. At $.745 per CCF the cost is about $.68 per hour. From the input rating data (100,000 BTU/hr) I calcualted .97 CCF/hr. So the actual gas consumption was a little bit less that the input rating. Now some Notes: 1. My gas bill is broken down to a charge for gas consumption, a customer service charge of like $21 a month and of course the tax on the consumption charge. So it's pretty straightforward how much the gas costs per hundred cubic feet. This month gas was $.745 per CCF. 2. No other gas consuming appliances(oven, stovetop or hot water heater) were firing at the time of testing. 3. I understand that outside temp, thermostat setting and how well my home is insulated are factors as to HOW OFTEN the furnace will run. That wasn't my concern. I only wanted to know how much gas was consumed when the furnace ran for an hour. How that hour was achieved was not important. It could of been 60 continuous minutes or six 10-minutes cycles. In my case I took a 10 minute run cycle and multiplied that amount of gas usage by 6. I have since I've hooked up the following 24V hour meter to the gas valve: http://www.grainger.com/Grainger/REDINGTON-Hour-Meter-2PPV9?Pid=search The meter progresses in tenths of an hour increments anytime the gas valve is open. I can tell how long the furnace runs each day, month or season. This helps with filter changes also. I've found that about every 125 hours the filter is dirty enough to be replaced.

A question for those who know more - is there an issue of pairing the coil (size/brand/airflow requirement or capacity) with an existing furnace? When I recently had new furnaces and AC put in, the contractor said that the expected "spec'd" furnace model for my house (in a mild winter area) didn't have enough airflow for the higher sized A/C coil and condenser needed. It was easy enough for him to use an appropriate model without upsizing the furnace output but it was a consideration. Back in the day of single stage furnaces you would have the gas heat blast effect for certain homes because the air flow needs for the AC were higher and pairing of a large furnace to meet those needs would result in blasting heat / short cycling of the furnace. Little you could do to rectify that problem back then. Many would use manual dampers and have to readjust them between spring and fall. They would often times sell maintenance plans based on this problem. However, this climate can some years be hot one minute and cold the next. Switch so often that you're doing the tango between areas of your home and the thermostat. (manual dampers are not a solution for that reason.) Now 2 stage gas furnaces rectifies this problem by running in low fire. If the furnace heat capacity is oversized for the home to operate the AC air flow needs it won't matter as the furnace will never run long enough to hit stage 2 high fire. Problem is occasionally you come across people who like the heat blast of older furnaces and complain the new furnace doesn't put out enough heat. There are ways to over come this as well, but you have to communicate often times to discover what the actual complaint is about.