Hi all. We are looking to replace our old furnace. We have had a few estimates and now we are trying to decide between an 80% and 90% efficient heaters and 1 stage / 2 stage / variable models. The price difference between 80% and 90% seems to be about 600-800 for Trane. The price difference between different stages is also several hundred $$$. How do we make a decision whether it is worth money to go with a more expansive model. I'm looking for a dummy-oriented advice as my knowledge here is pretty mich zero
First, I'll pull this homeowner question into alt.home.repair and set followups to it. I suppose you'll see why soon enough when some of the regulars go into Lord of the Flies mode. Yes, it's odd that a clearly hvac question is not welcome in such a named group, but what can ya do?
First, where do ya live, that helps focus how much heating this furnace is going to be doing. How long do you plan to stay in the home is another factor, as it determines whether the payback period for additional efficiency will every be enjoyed by you.
The best I can divine from a variety of resources as I was through similar decisions, 2 stage and variable speed are mostly comfort benefits. 2 stage is relatively simple--it's just that the gas valve has two settings. You run mostly on the lower setting until it gets damned cold or you're trying to heat the house from a set back temperature. This prevents the furnace from short cycling, and gives you less dips in temperature, may prolong the life of the heat exchanger and blower. It doesn't seem to come at much risk of adding to maintenance later as the mechanism seems to boil down to a gas valve that has Off, low and high settings, and some control logic that dictates when to kick it into high.
Variable speed seems to be contentious. It too is to afford you more comfort and better ddistribution of heating and cooling by keeping air cirulating in the house without having to have the noise and electricity use of running a single speed fan full bore all the time. Whether the energy savings translates into $ savings is subject to some debate since some point out that variable speed motors are very expensive and have a lot more stuff to break on them, while single speed motors have a long history and are pretty simple and relatively inexpensive. Others say variable speed is the cat's ass and makes a huge comfort difference. Other benefits include that you can keep your air moving and achieve better filtration as such, and supposedly you get some added dehumidification benefits as a variable speed's continuous air flow will keep things less humid in the AC season as air is circulated over the cold coil in the periodcs the A/C is off.
80 vs 90%. Take a look at your gas bills. Try to divine how much you use each winter for heating. Figure out how long it'd take to get your money back if your gas usage was 12% lower for the heating portion. Also factor in that for the installation they'll need to run some PVC pipe to vent outside out house as the 90% won't use your existing flue, but are so efficient they vent out PVC. There is some concern that higher efficiency furnaces are less reliable and may cost more in repairs down the road. I haven't yet determined if that's a real concern or not myself. Finally, take your crystal ball and divine whether you see current natural gas prices staying relatively flat, or increasing in the future. This also plays into the packback scenario.
All that said, I've also been told yo're better off energy wise with a
2-stage 80% than a 1 stage 90% at least in my situation, since the 2 stage will achieve comfort perhaps at a lower thermostat setting due to the longer cycle and better heat distribution to the extremities of your duct system that will result.
I'm sure I managed to utter some misconception or errors in all this info that will be mercilessly shredded by folks less interested in helping you and more interested in being able to be right by pointing out something that's wrong, but I hope you found some of this helpful in figuring out what's best for your situation.
The advantage variable speed gives with regard to dehumidification has nothing to do with air being circulated over the cold coils when the AC is off. How can the coils be cold when the compressor isn't running?
Variable speed can reduce humidity during periods when it's humid and it's not very hot. During those periods, the blower can run at low speed, which results in the air dropping more in temp as it passes through the evaporator, thereby condensing more water without cooling the house down a lot.
It also requires a multi-speed compressor to realize the dehumidifying benefit, with both the compressor and the fan at their lowest speed, it is very effective, inexpensive and doesn't cool the house much.
Have I missed something, why is Todd being beaten up? His info in variable speed 2 stage furnaces mirrors my experience. He seems to be laying out the pros & cons fairly. I do think the comfort thing is underrated, if that is unimportant why even live indoors?
This has less to do with reason and more to do with the very strange dynamic of alt.hvac where the thread originated. If I had to guess it's that I was a poster who was new to the group, a homeowner rather than an hvac pro, and who has an engineering degree, all in an environment hostile to all of the above. There are some good eggs in that group though, and kudos to them.
I'm admittedly trying to get a handle on all these pros/cons myself and just wanted to give Gene something to start with since the history of that particular group netted a very low signal to noise ratio.
I appreciate the clarification on the dehumidification benefit and what exactly is going on there.
The trouble with some of these questions appears to be that even among folks who ostensibly know their craft, there seem to be a lot of opinions on things that don't seem to match up, and figuring out if you're getting advice from a critical thinker with experienc or someone parroting marketing materials and junk science is difficult at best.
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