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Old 08-06-2011, 04:21 PM   #16
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sizing choice on system upgrade


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Originally Posted by raylo32 View Post
I think I already know what I need BUTH and tonnage wise, which is about what I have. I believe the the sizing is pretty close to being on the money. No need to reinvent that wheel. My questions are mostly trying to get at how these mod units work to vary their outputs and how to how to expect the blower speed/burner rampings to behave. Without any real control of the invisible algorithm on the Yorks I am convinced I don't want to get a unit with a blower that is a lot more powerful than what I have. I had a friend that just has his system replaced last Thursday (Trane - not sure if mod or just multi-stage) and his wife is already complaining about the roar on high speed A/C.
Hey,you tell them Raylo.
I believe in your right to believe anything you want to believe.
Of course I still believe in Santa Claus.I asssume you do too.

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Old 08-06-2011, 04:33 PM   #17
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sizing choice on system upgrade


I know that. My OLD furnce is the old air sucker. The new one will save me from heating all that cold air infiltration.

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Direct vent units still use outside air for combustion, either piped directly into the combustion chamber or next to the furnace.
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Old 08-06-2011, 04:34 PM   #18
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sizing choice on system upgrade


Cool, what do you want for Christmas?


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Hey,you tell them Raylo.
I believe in your right to believe anything you want to believe.
Of course I still believe in Santa Claus.I asssume you do too.
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Old 08-06-2011, 10:29 PM   #19
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sizing choice on system upgrade


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3 level all above ground 2500 sqft townhouse with split system : "Builder's model" Bryant 84K BTUH input (67k output) gas furnace, 3 ton A/C. I have lived here for 16 years and I believe the system is sized properly for my heating and cooling loads. This system has a 1/3 hp blower in a size B (17" wide) cabinet. I don't see a CFM rating on the label but I bet it is 1200 or so.

So, new system I am considering is a York Affinity modulating furnace 3 tons AC, 80k input (but 95% eff, so 76K output) furnace in a "4 ton" size C (21") wide cabinet and a 1600 cfm rated blower. My plenum is actually sized so this would fit perfectly, I'd just have to have the sheet metal opened up a bit on the adapter that was made to mate the plenum to the existing 17" cabinet.

My question is the blower. The new York system documentaion shows a couple jumpers to downrate the blower speeds for high cool and low cool (it is a 2 stage cooling system) to better match the installed AC. That seems simple enough to dial in the proper airflow for cooling to match the condensing unit and the ducts. Table has about 10 combinations.

But my question is for the heat cycle... do the settings chosen by the jumpers also affect the speed ranges that the blower will use and modulate around when in heat mode? If not and it uses full speed, will the modulating feature keep the blower from running at full blast most of the time?

Not sure about the tech specs on the ducting. These were builder homes and some of my neighbors have a 4th floor and got 4 ton units. So I wonder if we all got the same ductwork that is indeed adequate for the 4 ton homes. The plenums at least are the same.

Alternatively I could get the same unit in a size B 1200 cfm unit that would more closely match what I have now, at the expense of a point of SEER for AC mode with the smaller coil.

I realize these cfm ratings are just nominal values and actual values depend on many factors including the ductwork. I understand that a tech could get velocity and pressure readings to verify if necessary. I am just trying to get a ballpark feel for now assuming the original design was decent, which I think it is.
1) Unit needs to be properly sized to get the best effect/performance from it

2) The Lennox SLP you can tweak/adjust the blower speeds on 2 stages / in 2 steps /scenarios/ including the mod feature , (gets a bit technical if you have never seen or set one up) + or - 15% which can get you a quieter operation. All depends on the heat rise permitting that to be allowed. If it is running too hot due to undersized ductwork then you need to put it back to the norm setting.

3) Lennox does not sell to anyone other than their approved contractors so DIY with them is out of the question.
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Last edited by yuri; 08-06-2011 at 10:36 PM.
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Old 08-07-2011, 01:35 AM   #20
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sizing choice on system upgrade


No no no,he believes he has the right size already.Believing always trumps knowing for sure.
We all know that doing the calc is almost impossible to do.Its so hard that mere mortals would have no chance at it.
Knowing the exact size his house would distroy his belief system and leave him a wounded human being for the rest of his life.
ALSO HE IS RICH AND PAYING MORE THAN HE NEEDS TO FOR ENERGY IS HIS RIGHT,no matter how high the energy costs get to in the next 20 years.Its only chump change for him anyways.
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Old 08-07-2011, 06:33 AM   #21
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I am definitley paying too much for energy with my old system and I don't like it... but the payback with a new efficient system isn't a sure thing. First the cost of a new system is a lot of $$, then if some complicated bit fails outside of warranty the math goes south fast. So it it more a matter of comfort and not wanting to hang onto an old system too long and have it fail at the worst possible time. Isn't that how it always happens?

I have a friend who moved into their house the same time I did and got one of those fancy ground source heat pumps. He has put ~$10,000 into it for repairs and replacment parts in the 16 years, while all I have had to do with my basic split gas system is replace the dual run capacitor ($20) and put in 2 lbs of R-22 (free from a friend). Who got the better deal? My only regret with my system is that the builder didn't spec a higher efficiency furnace.

But I am still surprised their aren't codes that require that 90+ furnaces be used when the structure allows for its installation. I have another friend whose A/C failed (indoor coil blew out) last week during a bad heat wave. He ran home and his wife was on him to get 'er done. Trane contractor came out and sold him a system with an 80% furnace unit... my friend didn't even know the difference or that 95% units were available and install would have been easy in their house. But they had the existing type B vent in place so the contractor may have just decided not to try to upsell, which would also make more work for the install for them. I don't know since I wasn't there. Anyway, that's a lot of heating efficiency they are missing out on... and a lot of gas that will be wasted.


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No no no,he believes he has the right size already.Believing always trumps knowing for sure.
We all know that doing the calc is almost impossible to do.Its so hard that mere mortals would have no chance at it.
Knowing the exact size his house would distroy his belief system and leave him a wounded human being for the rest of his life.
ALSO HE IS RICH AND PAYING MORE THAN HE NEEDS TO FOR ENERGY IS HIS RIGHT,no matter how high the energy costs get to in the next 20 years.Its only chump change for him anyways.

Last edited by raylo32; 08-07-2011 at 07:12 AM.
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Old 08-07-2011, 06:40 AM   #22
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sizing choice on system upgrade


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Originally Posted by raylo32 View Post
I am definitley paying too much for energy with my old system and I don't like it... but the payback with a new efficient system isn't a sure thing. First the cost of a new system is a lot of $$, then if some complicated bit fails outside of warranty the math goes south fast. So it it more a matter of comfort and not wanting to hang onto an old system too long and have it fail at the worst possible time. Isn't that how it always happens?

I have a friend who moved into their house the same time I did and got one of those fancy ground source heat pumps. He has put ~$10,000 into it for repairs and replacment parts in the 16 years, while all I have had to do with my basic splict gas system is replace the dual run capacitor ($20) and put in 2 lbs of R-22 (free from a friend). Who got the better deal?

But I am still surprised their aren't codes tha require that 90+ furnaces be used when the structure allows for its installation. I have another friend whose A/C failed (indoor coil blew out) last week during a bad heat wave. He ran home and his wife was on home to get 'er done. Trane contractor came out and sold him a system with an 80% furnace unit... my friend didn't even know the difference or that 95% units were available and install would have been easy in their house. That's a lot of heating efficiency they are missing out on.

So has your friend saved more then 625 dollars a year on his heating and cooling bill with his geo? If so, he is still a head of the game in operating and repair cost.
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Old 08-07-2011, 07:00 AM   #23
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Thanks, Yuri. That sounds similar to the adjustments with the York and I understand that if the temp rise gets too high you are operating nearer the safety cutoff. Probably don't want to push that limit to allow for variation like dirty filters and such

DIY... not sure I would take this on, but I might... unless my current system fails at the proverbial worst time, which always seems to be the case and I need to get it done fast. And one benefit of DIY is that if something isn't done perfectly I will know who to complain to and that they will listen. ;-)

I have done my own A/C maintenace forever, done my cars A/Cs forever, have my EPA cert, have some but not all of the tools etc. I'll probably get a couple of quotes but am in no hurry yet since my current system works fine. I am just thinking about how nice a new mod or VS furnace would be in the winter... not having all those cool periods in between the relatively short single speed furnace runs would be so nice....

I appreciate you guys helping me understand how these mod furnaces work. Sounds like great technology.


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Originally Posted by yuri View Post
1) Unit needs to be properly sized to get the best effect/performance from it

2) The Lennox SLP you can tweak/adjust the blower speeds on 2 stages / in 2 steps /scenarios/ including the mod feature , (gets a bit technical if you have never seen or set one up) + or - 15% which can get you a quieter operation. All depends on the heat rise permitting that to be allowed. If it is running too hot due to undersized ductwork then you need to put it back to the norm setting.

3) Lennox does not sell to anyone other than their approved contractors so DIY with them is out of the question.
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Old 08-07-2011, 07:10 AM   #24
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You know, he might be ahead of the game because I think (but not sure) that they don't have gas in their neighborhood so otherwise would have to have an air souce heat pump with resistance backup. Their house is extremely well insulated. I'll have to ask him if he has done the math.

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So has your friend saved more then 625 dollars a year on his heating and cooling bill with his geo? If so, he is still a head of the game in operating and repair cost.
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Old 08-07-2011, 10:10 AM   #25
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In Canada every new house has to have a 90% efficient furnace, 92% in Manitoba and 95% may be here as a standard soon. Other options are electric (very expensive) oil and propane (ridiculously expensive) and geothermal which start around $25,000. Heat pumps and elec in Southern Ontario and BC but electricity to run them is still expensive.
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Old 08-07-2011, 10:23 AM   #26
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I think standards like that are a good thing. The equipment price difference between 80% and 90+ % isn't all that much so no reason to get 80% unless there is absolutely no way to run the direct vent for a high eff unit.... or maybe if you live in warm region that doesn't need much heat. It still bothers me to see energy just wasted, though. I am glad to live in a relatively moderate area where we actually usually have a few months where we generally need neither heating or cooling. That is the time to do system replacement if one can plan it. I can't even imagine having to heat a place in the Great White North.


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In Canada every new house has to have a 90% efficient furnace, 92% in Manitoba and 95% may be here as a standard soon. Other options are electric (very expensive) oil and propane (ridiculously expensive) and geothermal which start around $25,000. Heat pumps and elec in Southern Ontario and BC but electricity to run them is still expensive.
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Old 08-07-2011, 10:29 AM   #27
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Yes heating a place in the great white north can be tricky, get it too hot and it starts to melt the walls......
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Old 08-07-2011, 10:30 AM   #28
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Depends on how new and well built your house is up here. Buildings standards have got VERY high here with glued on vapor barrier etc etc. I have 2x6 walls R20, R40 in the attic, low E argon windows and can heat my house for under $100/month in the coldest 4 months. AC costs are cheap here as it gets cool at night and we shut em down. There are people paying $200-300/ month to heat 100 yr old houses with old hot water boilers. Some of them converted from coal to oil and then gas. Not sure how they afford that but they like that comfy feel of old cast iron radiators beaming the heat out all the time. Does not help to have sawdust for insulation in the walls and poor windows too.
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Old 08-07-2011, 10:33 AM   #29
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Yes heating a place in the great white north can be tricky, get it too hot and it starts to melt the walls......
NO JOKE. You can tell the poorly insulated houses by looking at the roof. If all the snow has melted and you see huge icicles hanging down then you know the guy has no attic insulation.
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Old 08-07-2011, 10:36 AM   #30
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Just another thought on the whole sizing discussion... With the flexibility of the modulating systems I wonder why mfgs don't have adjustments to tweak the algorithms... like Beenthere and I were discussing the choice between 60k and 80 BTUH furnaces and I understand the importance of getting the correct size, esp with old "dumb" equipment. But since a mod furnace can run in a very wide BTUH range why not have a couple of selectable profiles that could fine tune the algorithm? Say you could choose an algorithm for an 80 K BTUH nominal unit to not go above 65K, 70K, or 75K BTUH, or whatever. Seems something like that could be easily accomplished in firmware and allow fewer sizes of furnaces to cover a wider range of applications. Less parts inventory, more fine tuned operation... all accomplished with a few changes in the firmware.

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