How to make sense of the choices? Thread split off.

[RoBoTeq]

Makes sense on the 6" flues and the gobs of additional dilution of air can no way be as efficient as a induced draft furnace that has controlled air volume, even steady state. The flue gases still have to be at a certain temperature to prevent condensation/rust out. I do find it odd that manufacturers listed a bonnet capacity without a means to change what the actual output of the furnace is. I don't see any way to increase the bonnet output without overfiring the furnace or doing other modifications. Not sure what the point of even listing bonnet capacity is since if it cannot ever be achieved.

For load calculations, rough guides like "Heat is 2X AC" you posted earlier tend to be the rule rather than the exception. For cooling Contractors typically use 500sqft per ton without regard to house construction, insulation, or even age. Only older homes (pre-1970) really need 500sqft per ton of cooling, new construction can get away with as little as a ton per 1,000sqft per ton if it's built right. A full load calculation is almost like a unicorn in our area. Correctly designed ductwork may possibly be even more rare, we see a LOT of ductwork "wall of shame".

Interesting that you admonish me for my "rule of thumb" (incorrectly quoted while ignoring that it was posted strictly as a guideline for how to tell if your furnace is most likely too large), and then you completely ignore telling us how you make your determinations about furnace capacity in your area. Nice dodge....

Since your area does have average temperatures dropping below freezing with cooling averages during July and August in the low 90's, there is not that much difference between where you are and where I am.

Since you insist on continuing to admonish HVAC contractors on this site, at least have the courtesy to tell us how you come to your conclusions that so many of us don't know what we are doing. Hopefully, you can do that without directing us to another DIY home improvement site as your source of information.

[54regcab]

I do believe there is plenty of quality work being done by contractors who take pride in their work (see wall of pride forum). However I see a lot more work that qualifies for "wall of shame". Unfortunately the lowest bidders get too many of the jobs and the work is marginal at best. Apartments and rent houses tend to be the worst around here. I don't have anything against the HVAC profession or I wouldn't have chose it as a way to make a living. I just a have a pet peeve with work not being done right.

Furnaces around here are constantly oversized, but most customers are used to it and few complaints are generated from the uneven temperatures and higher utility bills. Customers only complain when the furnace starts kicking of on the high limit switch and it shuts off power to the thermostat (if it's hardwired, on battery stats they normally don't notice). Normally this is due to marginal ductwork, sometimes due to dirty or overly restrictive air filters.

I'm surprised to see that your high temperatures in PA are close to ours in summer, and your winter temps are also similar. I would have thought it would be much colder that far north. I don't know where you are in Eastern PA, but years ago I lived in Carlisle PA and remember having to wear a coat to my senior graduation in 1989. We had no AC installed our house and many neighbors didn't either. You don't find many houses in Oklahoma without at least a window AC. While in PA I also remember the lake freezing so solid you could walk on the ice, something that's never happened in Oklahoma in the 10 years I've lived here. Carlisle also plowed ALL the roads, not just the highways and snow routes. Perhaps global warming has made both climates hotter over the past 20 years, but part of me thinks global warming is government propaganda. We did however have 18 days in a row over 100 degrees last summer, and going into attics really sucked those days. Here's a link showing how hot it got the past 2 summers, how does eastern PA compare?
http://www.srh.noaa.gov/oun/?n=climate-okc-heatwave

[54regcab]

How are furnaces and AC's sized around here? They SHOULD be sized using a proper load calculation program, unfortunately it doesn't happen that way in most cases. Typically AC is sized 500sqft per ton, then a furnace that has enough blower capacity is selected. To get a certain blower size for the AC means buying a certain minimum BTU capacity for heat. Then there is the issue of what the supply house has in stock, normally it's the high BTU for a given blower capacity that gets installed. You can buy a 50k furnace with a 1200CFM blower, but a 75K with a 1200CFM blower may get installed instead because that's what the supply house has in stock/on sale at that time. Doesn't matter that the house only needs 40K of heat according to a load calculation. Doesn't matter that the ductwork can only deliver 800CFM of air and the furnace will cycle on limit come winter.

I'm not sure if you see that many poorly done systems up north, I sure hope not. I'm sure you have had to go behind at least a few installs done wrong, shaking your head of why it was done this way. Hopefully you're pleased when you run into an exceptional job well done and everything is easy to get to and service. As we have all said to customers, it's the INSTALL that matters more than the brand of equipment

[Mr Bill]

.You can buy a 50k furnace with a 1200CFM blower, but a 75K with a 1200CFM blower may get installed instead because that's what the supply house has in stock/on sale at that time. Doesn't matter that the house only needs 40K of heat according to a load calculation. Doesn't matter that the ductwork can only deliver 800CFM of air and the furnace will cycle on limit come winter.

Here's what doesn't matter, the load calc doesn't matter if they are not addressing the duct work. Why waste your time with a load calc if your not going to correct the duct design? your just wasting your time and the customers time. If you have some dummy installing a system that the duct is so insufficient that the furnace goes off on high limit, you don't address it with a smaller cfm furnace, because airflow is also important to the cooling performance, low airflow= low performance. You folks must have a great job security up yonder, with all the HX warranties. This is why we call them A/C and Heating "systems" the duct work is part of the system.

[beenthere]

Here's what doesn't matter, the load calc doesn't matter if they are not addressing the duct work. Why waste your time with a load calc if your not going to correct the duct design? your just wasting your time and the customers time. If you have some dummy installing a system that the duct is so insufficient that the furnace goes off on high limit, you don't address it with a smaller cfm furnace, because airflow is also important to the cooling performance, low airflow= low performance. You folks must have a great job security up yonder, with all the HX warranties. This is why we call them A/C and Heating "systems" the duct work is part of the system.

In my area, usually the furnace can be down sized, so the old duct system is more then adequate for the new furnace. pretty much the same for the A/C. Old A/C might be 3.5 ot 4 tons, and the house only needs a 3 ton, and the duct work is ok for a 3 ton, or only takes the adding of a return, or a minor alteration. So if the same size equipment would be put back in, all they would have is a new same size system that isn't working any better then the old system did.

That said. there are those small homes that have a 60,000 BU 80%er and a 1.5 ton A/C where the home owner says it heats fine and it cools fine. I don't bother with a load calc on them, I put the same size back in.

[54regcab]

Here's what doesn't matter, the load calc doesn't matter if they are not addressing the duct work. Why waste your time with a load calc if your not going to correct the duct design? your just wasting your time and the customers time. If you have some dummy installing a system that the duct is so insufficient that the furnace goes off on high limit, you don't address it with a smaller cfm furnace, because airflow is also important to the cooling performance, low airflow= low performance. You folks must have a great job security up yonder, with all the HX warranties. This is why we call them A/C and Heating "systems" the duct work is part of the system.

Totally agree, poor ductwork needs to be addressed and corrected before any new equipment is installed. If ductwork is OK, but just undersized downsizing the equipment like beenthere suggests works well also.

[BadgerBoiler MN]

Every heating/cooling appliance must be properly sized to the load. The load is properly determined by performing a Manual 'J' heat load. Furnaces with higher cooling loads will require higher blower speeds - while in cooling mode - but they make furnaces with multiple speeds; one low fan-on, one heating; a bit higher, and one for cooling; typically the highest speed. Then of course there are variable speed ECM fans burners or less expense two-stage furnaces.

Once you have the heat load the duct work can be addressed. It does pay to look at the whole system before starting. There is no excuse for installing heating equipment more than 150% of the heat load or for that matter installing any piece of heating equipment without performing a manual 'J' first. This is how the homeowner should determine which furnace to choose.

It is the dealer not the furnace.

[54regcab]

BadgerBoiler MN, what we run into in the south is trying find a furnace with enough blower capacity for cooling, but without oversizing on the heat side. Some manufacturers don't offer their nicer furnaces in sizes under 60K. No manufacturer that I can think of offers a 80% furnace 50k or under with a variable speed blower. The VS feature is nice for those of us in the south, and it's not cold long enough to justify the cost of a 90%+ furnace.

[BadgerBoiler MN]

Point taken. But here in the north country when we face small heating loads we size for cooling and put a cased coil in the plenum and drive it with the water heater.

[54regcab]

Using the water heater/coil for small loads works great. For some reason they aren't popular around here so local suppliers don't stock them. I've seen the concept online, but haven't found a good source/manufacturer for a residential product. Firstco makes them as part of the air handler. IEC which is in Oklahoma City manufacturers them, but they focus on commercial. My wife used to work there and got a unit that they were using for testing purposes once they were done with it.

[BadgerBoiler MN]

Yes. First Co. makes nearly every size of coil both single and pumped packages.

[RoBoTeq]

BadgerBoiler MN, what we run into in the south is trying find a furnace with enough blower capacity for cooling, but without oversizing on the heat side. Some manufacturers don't offer their nicer furnaces in sizes under 60K. No manufacturer that I can think of offers a 80% furnace 50k or under with a variable speed blower. The VS feature is nice for those of us in the south, and it's not cold long enough to justify the cost of a 90%+ furnace.

Now you are just fabricating specifics to complain about. Why are you looking specifically for an "80%" furnace "under" 50K with a variable speed blower? Are all of the houses in OK City under 1,000 square foot bungalows? You keep pinpointing specific applications where it is difficult to obtain the specific furnace you want to complain about. What is wrong with working in a positive manner with what is available? As I have stated before, you seem to just want to dwell on something to complain about HVAC professionals. Just what is it you do that you feel you work in the HVAC industry? You have already posted an entire thread telling us how you DIYed in a cooling system to an existing oversized heating system. Just what is it you do that is HVAC related on a daily basis?

[RoBoTeq]

There are dozens of hot water coil manufacturer's in North America. Multi coil, USA coil, Diversified etc. And there are plenty of hydronic air handlers as well; Rheem, ADP, Goodman etc. I did hydronic coil heating for certain applications for decades in the Baltimore/DC corridor, and I'm getting more and more HVAC contractors, especially those with a plumbing background, to do more of them in PA.

In fact, I don't have it operational yet, but I have a hydronic coil in the supply plenum of my own home heat pump that will eventually be connected to a tankless LP hot water system.

[54regcab]

There are dozens of hot water coil manufacturer's in North America. Multi coil, USA coil, Diversified etc. And there are plenty of hydronic air handlers as well; Rheem, ADP, Goodman etc. I did hydronic coil heating for certain applications for decades in the Baltimore/DC corridor, and I'm getting more and more HVAC contractors, especially those with a plumbing background, to do more of them in PA.



In fact, I don't have it operational yet, but I have a hydronic coil in the supply plenum of my own home heat pump that will eventually be connected to a tankless LP hot water system.

I'm glad to see the hydronic coils are becoming more popular, and you are promoting them. Have you done any systems that use multiple air handlers? On your setup will the water heater be doing your domestic hot water also?

[Mr Bill]

Why are you looking specifically for an "80%" furnace "under" 50K with a variable speed blower? Are all of the houses in OK City under 1,000 square foot bungalows?.

I think he is talking about the typical home in his neighborhood.

[54regcab]

Now you are just fabricating specifics to complain about. Why are you looking specifically for an "80%" furnace "under" 50K with a variable speed blower? Are all of the houses in OK City under 1,000 square foot bungalows? You keep pinpointing specific applications where it is difficult to obtain the specific furnace you want to complain about. What is wrong with working in a positive manner with what is available? As I have stated before, you seem to just want to dwell on something to complain about HVAC professionals. Just what is it you do that you feel you work in the HVAC industry? You have already posted an entire thread telling us how you DIYed in a cooling system to an existing oversized heating system. Just what is it you do that is HVAC related on a daily basis?

I would have like to have one of those furnaces for my own 1600sqft house. 50k isn't just for small houses, it can serve over 2,000sqft IF it's insulated right. Ask any of the building science guys about this one. Gas around here is cheap (less than 50 cents per therm), so anything over 80% doesn't have a reasonable payback time. The variable speed feature is mostly for comfort reasons, even though the payback time on that is long.

In a daily basis I work with the Smarthours project. We install the Smarthours thermostats and run service calls when the customers call in if it doesn't work correctly. We don't repair the HVAC units or install new ones as part of this project, we just determine if the problem is with the thermostat or HVAC unit. As part of the project we see the good, bad, and the ugly as far as installs go. Some installs are excellent, others are so bad we don't even do the thermostat install for liability reasons. Most are in-between.

Since our thermostats are system powered they go blank when a furnace shuts off on high limit, and then we get a service call. People are quick to blame our thermostat because the old battery power stat it replaced just let the furnace cycle on high limit and the customer didn't know the burners were switching off because warm air continued to come out of the vents and the thermostat "stayed on". Since the furnace is often oversized to begin with the house still stayed warm even though the burners were shut off on high limit 1/2 the time. After seeing a bunch of these through the winter it does give me prejudice to the combination over-sizing of furnaces and poor ductwork design.

[54regcab]

I think he is talking about the typical home in his neighborhood.

We get plenty of jobs that are on houses not much better than this. Not fun, but a paycheck is a paycheck...

[Mr Bill]

Since our thermostats are system powered they go blank when a furnace shuts off on high limit, and then we get a service call. People are quick to blame our thermostat.

What brand/age of unit are you talking about that the "high limit" kills the power to the stat? all the high limit does on any newer "board type" unit is break the circuit back to the board, the lugs on the board receive direct power from the thermostat.

[Mr Bill]

What brand/age of unit are you talking about that the "high limit" kills the power to the stat? all the high limit does on any newer "board type" unit is break the circuit back to the board, the lugs on the board receive direct power from the thermostat. .

Edit: I said the lugs on the board receive direct power from the thermostat, correction, the lugs are powered directly from the transformer, and the thermostat is powered from the lugs, so the high limit would not effect power to the stat.

[54regcab]

What brand/age of unit are you talking about that the "high limit" kills the power to the stat? all the high limit does on any newer "board type" unit is break the circuit back to the board, the lugs on the board receive direct power from the thermostat.

Most of the ones we see this problem on are the newer Carrier/Bryant/Payne 80% units. Not sure of model numbers, but they are under 10 years old. It's the style that uses a thumbscrew to hold the large main door on, and the blower/board are behind a sub panel. Diagnostic code of "33" when it shuts off the burners on high limit and kills the 24V to the thermostat. Blower continues to run while on high limit. Once the furnace cools back down power is restored to the thermostat. This is not the only furnace that does this, just the most common one we see for high limit shutoff. When testing, the discharge air from the registers gets to about 130 degrees before the furnace kicks off on high limit.
http://www.sbeelectricandhvac.com/do...-310aav-error/

I've seen a few old pilot light furnaces cut the power to the primary side of the transformer when out on high limit. Not very common, I think most do like MrBill says and just kill the power to the gas valve. Not sure how many just kill power to the gas valve because we get very few calls on them. We see more of he induced draft style furnaces when it comes to high limit shutoffs, I'll start paying more attention to which brands/models I'm seeing.