just go wityh the 90% furnace. it will cost you more to change the design than the price difference in furnaces
I just took my home plans to the county building department to begin the plan check process. I noticed (a little late) that the architect had indicated a 90% furnace. My plans had been to get an 80% furnace and a higher SEER AC given my area which has mild winters and hot dry summers.
My understanding by reading some posts here was that, unless money is no object, you should match the higher efficiency unit (AC or heating) to your most extreme weather condition. So if my winters are mild I would not necessarily benefit from a higher efficiency furnace as much as a higher SEER AC to deal with my hotter summers.
When I asked the building permit technician if the architect's specs for a 90% furnace could be changed he told me I would have to have another energy calculation.
Does this sound right to you? Is there a connection between an energy calculation (Manual J) and the efficiency ratings of the equipment?
I thought, perhaps in error, that the calculation had to do with capacity, not efficiency.
In any case, I left the plans and will ask the architect on Monday.
just go wityh the 90% furnace. it will cost you more to change the design than the price difference in furnaces
I dont think the load changes but the furnaces are rated by input, not output. For instance a 100,000 btuh 90+ would have an output of say 92,000 btuh and a 100,000 80+ would have an output of something like 82,000.
The manual J wouldnt change, the requirement stays the same but the Btuh input may change as a result. The energy calculation may just be a calculation on how much they anticipate you spending on fuel which may indeed change.
Go with the 90+ anyway.
You are right, there is no technical difference from a 90% or an 80% as far as the amount of btu's needed to heat the home. However, due to losing 10% of your output, you may well have to use a larger furnace which might cause the need for ductwork changes, as well as changes in the exhaust.
I guess it will all come down to money. I wanted to get a VS furnace as many on this site (including docholiday) has sold me on the comfort benefit. Combining 90% and VS will increase the cost of the system.
Ah, well, I'll just work a little harder.
Thanks for the advice.
You can get a VS in 80.
Doc, that would involve getting the architect to do another calc, right?
I'm assuming (always dangerous) that there are national and maybe state minimum ebergy standards. I know that a 13 SEER requirement is coming up and 80% (or is ti 78%) is the current minimum on furnaces (is this right?)
I probably discussed equipment rating with the draftsman. I probably told him I would like a 90% furnace and a 14 SEER AC. I just didn't think the efficiency rating (beyond the legal minimums) would be specified in the plan and that I would then be required to use equipment that met the efficiency ratings specified in the plans.
I dont recall your situation. If its new contruction it will require a chimney, there are alot of considerations.
No need to recalculate but why mess with an 80 with gas prices being 20-30% higher than just last year? I was just pointing out your options.
Doc, how does all this relate to the AC? Let's say I get a VS furnace. Does this have anything to do with the speed of the AC blower? I know this shows my ignorance, but some of the things I read on the Trane website seemed to indicate that in a split system (electric AC, gas furnace) that the furnace blower is involved in the AC fan or blower set up.
For example I might see a 2 speed AC unit and a 4 speed furnace on the Trane website. Could these work together?
Yeah 4 speed furnace fan is ok but it partially defeats the purpose of two speed cooling which is comfort, why cripple an upgraded system with a PSC motor?
You need to be asking the Trane guys this stuff, I always see the comments "Trane,..there is no subsitute" but I rarely find much in the way of support for this statement.
I don't quite understand. If I have a VS furnace does that affect the fan set up of the AC?
Could you give a HVAC 101 lesson on how the fan set-up of the AC and furnace work? Are they independent of each other, or is there is relationship between the fan of the AC and the fan of the furnace?
The furnace is the blower for the AC. It knows how to speed the blower based on configuration and thermostat input.
OK, so if I get a VS furnace I also have a VS AC?
As far as airflow goes, yes. But it doesnt make the AC itslef VS.
Nathan, i think the plan checker is referring to the cal. title-24 compliance forms,not a manual j.Your house might not have complied to the states model home effif.standards
with a 80% furnace,so by upgrading to a 90% furnace your house complied with the state model.Sometimes a home will have more glass area than is allowed so by increasing the furnace eff. you were allowed more glass area, If my typing makes any sence to you.
Doc, one last question (until next time). I know everyone has their favorite brands, and I'm good with the general recommendation that you go with the quality of the installer and not a particular brand of equipment.
Doc, let's say I've determined 2 equally qualified installers. One installs Trane and the other installs Amana. I know Trane has their staunch defenders and I also know Amana has been soiled by their connection to Goodman, at least in many minds.
Let's finally say I want a 90% VS furnace and a 13 or 14 SEER AC.
If I really could determine both contractors were equally good at the install then it seems as though I really do come down to an equipment question. And I know Trane guys are never going to admit Amana is as good as Trane, but at some point I'll have to make that call.
So, Doc. How much (I know there are no pricing questions) is a particular brand worth? I have a feeling there is no right answer. Just curious to see how much weight you would give to brand if significant price differences were involved.
Thanks, bigbird. That makes sense. I'll ask the architect's office on Monday.
I appreciate all the free advice. I can assure you in my line of work I don't know of such a forum where consumers can learn so much from a variety of practitioners.
Nathen9999.
The V/S motor is just that.It is the motor that makes the blower wheel go round and round.You can have a 80% furnace with a V/S motor.Or you can have a 90% funace with pse four speed motor.Keep in mind here the four speed motor is just that four fixed speeds.Of which you can only use only two speeds.One for the speed of the air when the A/C is on.One speed for when the heat is on.You can do a lot of calculating but on average a 80% two stage furnace with a V/S blower motor is the biggest bang for the buck.There are other reasons to use a 90% furnace.Such as noise and venting limitations.With the two stage heating V/S furnace you get the comfort and the saving of less energy used with a continuous fan.You use that for really good filtration.Then with the V/S blower motor you get all the + + + + that DOC has talked to you about.Like relly good humitidy control.Look at the installed price differents between a 80% and 90% V/S furnaces than look at how many years it will take to get back the price differents with a 10% more better burn:} With the money save on the furnace you could then buy a higher seer A/C or maybe a two stage A/C.Then you would get the killer comfort all summer long.
41GASMAN