RGRM-10EZAJS and RARL-049JEZ Oversized ?

[makeithappen]

This has been a long process of getting bids and information and now have a system installed and don't know if I need tuning or a replacement system. My fear is that this system is oversized for the property.

Denver Area
Home that was converted into 3 apartments
1892 two story 4 bricks thick - 1800 Sq Ft
The old porch was added on and ducts were added at some point 500 SQ ft
Once common heating forced air system in the cellar.

Displaced thermopride 162K input furnace probably 40% efficient (only saw it work briefly)
Property used to have a coal furnace years ago.
Installed RGRM-10EZAJS and RARL-049JEZ and NEST thermostat (1st floor)
Heat load document from the installer was 60K in a pie chart
APRILAIRE media filter, and bypass humidifier

1st floor two double sided heat vents 1 larger return
2nd floor, 4 heat vents (12 in round return added to this floor up high with this installation)
Rear porch apartment 500 sq ft, had two supples and not returns (added 1 return and 1 supply)

Issues:

Not sure how the selection of my unit size was determined

2nd floor is 66-67 degrees when 1st floor is 70 degrees
Addition is 66-67 degrees when 1st floor is 70 degrees
2nd floor 12" round return is LOUD (wind noise)

After installation furnace wind noise was LOUD especially the added return. I thought the benefits would be quiet operation. I asked if the blower could be slowed down. With the dip switches they changed it from 1400 CFM to 1150 CFM with of course increase in TEP rise, same BTU's. Same fan speed for 1st and 2nd stage by design.

Furnace could not be raised off the floor due to height restrictions and A/C coil. All of returns enter into the fight side of the furnace thru the filter.

My theory is this is an old house with small and few ducts from the old coal furnace and installing this size of the furnace means high CFM to cool the exchanges resulting in lots of noise. Looking at the literature seems a smaller unit could have been selected that still would have supported 4 ton blower for A/C.

Questions in my mind. Should this be downscaled to 90 or 75 K 2 stage unit
Should the returns be piped into each side of the furnace to quiet the return via another aprilaire filter
Static pressure (don't know what it is)
Do I need another supply in level 2
Would a 90K 2 stage running at 850 CFM be quiet enough
i was shooting for a well balanced system rather than a complicated three zone system with bypasses etc

Any input would be appreciated, or let me know what PICS I can supply. I have not called the installer back until I am a bit further educated here. It's not quiet or comfortable. Installation was careful, ducts all sealed, things done tidy, good reputation installer, just not sure this is sized or tuned for my application

Thanks !

[beenthere]

The idea of a 2 stage furnace is to have a slow gentle heat in first stage. Which also tends to help even out the heat in a house. Running it at the same CFM as second stage defeats that.

[BaldLoonie]

The furnace on high fire or cool will want to move around 1600 CFM. If you don't have a big duct system it will be noisy. I don't think that furnace will slow down to 1150 CFM on high heat, it would overheat and shut down. There is minimal control over heating blower speeds to protect the furnace. The 09 would want to move similar air. If you stepped down to the 07 with a 3 ton blower, you'll run around 1100 on high as I recall and be much quieter. But max out at a 3 ton A/C. But in your climate that may be all you need anyway.

If the heat loss was 60K, the contractor was a moron for putting in the big furnace. And if the heat loss was that low, the 4 ton was likely as grossly oversized.

[makeithappen]

The idea of a 2 stage furnace is to have a slow gentle heat in first stage. Which also tends to help even out the heat in a house. Running it at the same CFM as second stage defeats that.

That is what I thought. But a variable speed furnace really is only variable 2 times, slow startup and slow ramp down. Those are very short segments to avoid the noise of instant burst. After that it tries to run at a fixed CFM as defined by the dip switches on the control board. When you pick the CFM it is the same for stage one as well as stage 2. The difference being in my case, stage 1 delivers 73K BTUS where stages two give more gas and delivers 97K BTUs, My speed choices are 1400, 1200, 1250, 1050. However 1050 would deliver 70 degree temp rise on stage 2 which is pretty high.

Cooling speeds are independent of these "fixed" speeds on a variable speed furnace.

[makeithappen]

I think you are correct and my ducts are too small. If the heat loss is 60K and you are selecting a 2 stage furnace which do you select 50/70. 52/70, 63/84 or 73/97 all in KBTU's.

The heat loss was based on the 1800 main structure and did not account for the 500 sq ft addition. I should add that.

[beenthere]

That is what I thought. But a variable speed furnace really is only variable 2 times, slow startup and slow ramp down. Those are very short segments to avoid the noise of instant burst. After that it tries to run at a fixed CFM as defined by the dip switches on the control board. When you pick the CFM it is the same for stage one as well as stage 2. The difference being in my case, stage 1 delivers 73K BTUS where stages two give more gas and delivers 97K BTUs, My speed choices are 1400, 1200, 1250, 1050. However 1050 would deliver 70 degree temp rise on stage 2 which is pretty high.

Cooling speeds are independent of these "fixed" speeds on a variable speed furnace.

Variable speed blowers are not suppose to be use to use the same CFM/speed for first stage as for second stage. You are misinformed, and your furnace is not set up right. Running too high of a CFM in first sage can cause condensation in the primary heat exchanger and rot it out.

[makeithappen]

I'm looking at the manual that came with the furnace page 48 . Two position dip switches control the CFM exactly for stage one and stage 2. Stage 2 always delivers more BTUS to the home because it is the gas burner that provides higher output. If I can figure out how to post it I will.

[RoBoTeq]

You have a mess that cannot be fixed. You simply have too much overall heat, too much overall cooling and too much overall air.

It doesn't sound like anyone involved in the application and sizing process understands that staging is only for comfort and that sizing MUST be done based on TOTAL system capable capacity, not based on any low stage with extra "just in case".

There is no fix for your issue other than having the proper sized equipment installed.

[makeithappen]

100% Agree. It appear to be the wrong equipment. For heat loss, cooling as well as probably for the duct size.

[makeithappen]

What is very frustrating to me as a consumer is I was up front with what I wanted. In that I wanted a quiet low running system and did not want it to be oversized. Amazing I had 5 bids from reputable large HVAC contractors in the industry and their sizings went fro 80KBTU to 120K BTU's. Seems there is no science behind their work. This last one said they complete the technical sizing right before install. Had I known they were going to put this in I would have put a stop to it. It will be removed now and corrected.

[makeithappen]

So, setting aside the duct capabilities, CFM for one moment and we just talk about energy. If the heat loss calculation for a property is 60K what size of a 2 stage furnace is optimum? Sized to match at low, high or split down the middle?

[makeithappen]

Variable speed blowers are not suppose to be use to use the same CFM/speed for first stage as for second stage. You are misinformed,....

I do not believe your statement to be true. Is it possible you could provide some facts here. I am not an HVAC tech but I read the manual in the sections for setting the CFM and temperature rise and I do not believe that the blower speeds for Low and High fire can be set independently.

[tigerdunes]

Make it Happen

Can't add much to what's been said. Curious though. What mdl thermostat was installed? This furnace for optimal operation works best in a true 2 stage thermostat that controls heating stages not a timer on control board.

IMO

[rglasgow]

You are correct. The CFMs for high and low are not chosen independently but they are not the same CFMs. Whichever dip switch you choose will have two different CFMs. Even if you can correct the furnace, you still have a 4 ton ac if I understand your post.

[beenthere]

The blower speed for low should provide a reduction in CFM to maintain the same temp rise as in high. If your is using the same CFM for bot, something is wrong.

Your furnace may have been set up to only use second stage if you notice no difference in blower speeds.

[makeithappen]

The blower speed for low should provide a reduction in CFM to maintain the same temp rise as in high. If your is using the same CFM for bot, something is wrong.

Your furnace may have been set up to only use second stage if you notice no difference in blower speeds.

The furnace is using BOTH stages, only stage 2 if I make like a 3 degree delta T call for heat. Or at the tail end of a run. I am using the NEST thermostat generation 2 that supports 2 stage heat and 2 stage cooling as well has dehumidification/ Humidification. I am using 7 wire connection for 2 stage heat and 2 stage cool.

I have used the 1st generation NEST at another residence for a long time. At this 3 apartment unit I am talking about in this thread, it is vacant while I work this. So I can get good controlled data on the running of this. I can see the duty cycle and run times etc. In addition I have IZON camera's in front of themometers scattered throughout all three of the units. I also have a NEST generation 1 installed in apartment 3 (the 500 sq ft one) that I had as a spare. It is only hooked to 24 volts and not a heating system. In this way I can see the temperature that unit and get reports.

Sorry for all the info. I tried to paste page 48 of the manual to try and conclude this CFM discussion. As you can see the two position DIP switch controls 1 and 2.

[makeithappen]

I eat yummy crow and humbly apologize. The product specifications in another marketing document says high heat 1604 and low heat 1400. But I do not see that high of speed in the manual except for cooling mode. See what happens when a layperson tries to understand. At any rate because this sucker has to move air over the exchanger that is putting out either 74K BTUs or 92K bTUS it seems to have very high CFM and noise. Also the returns all seem to be racing to one side of the furnace. At 30 degrees outside, 70 degrees inside it stays in stage 1 heat mode and runs about 33% duty cycle. Just as a ref point aside from the noise.

[RoBoTeq]

Even the low fire is too much for your home. The Nest thermostat is a sophisticated off/on switch with programming that is dedicated to turn the furnace off as much as possible. This means that more often than not, the Nest is bringing the furnace on in high fire when it is not figuring out a way to keep it from running.

Also, no matter what, that furnace is forced into high fire every 12 minutes of run time. All staged condensing furnaces are forced into high fire with 12 - 15 minutes of run time to prevent damage to the primary heat exchanger.

If you are looking for any sort of comfort level from your HVAC system, you have the worst of the worst case system installed. The combination of everything being oversized and a t-stat that is only concerned with energy efficiency, you'd be better off with the old coal burning furnace.

Then again, the Nest stat is most likely not the only thing controlling your furnace's heat cycles. My guess is that during the colder days, the limit switch is what is turning your system on and off most times.

Go back to whoever sized and provided that large of equipment and tell them to take it out and put in the proper equipment.

[makeithappen]

Also, no matter what, that furnace is forced into high fire every 12 minutes of run time. All staged condensing furnaces are forced into high fire with 12 - 15 minutes of run time to prevent damage to the primary heat exchanger.

If you are looking for any sort of comfort level from your HVAC system, you have the worst of the worst case system installed. The combination of everything being oversized and a t-stat that is only concerned with energy efficiency, you'd be better off with the old coal burning furnace.

Then again, the Nest stat is most likely not the only thing controlling your furnace's heat cycles. My guess is that during the colder days, the limit switch is what is turning your system on and off most times.

Go back to whoever sized and provided that large of equipment and tell them to take it out and put in the proper equipment.

I'm not seeing high fire unless I turn the t stat up about 3 degrees. If I leave the t stat at 70 degrees and it is 30 degree nights and 50 degree days the duty cycle is about 33 percent. Roughly 20 min run 40 min rest. Your input of 12-15 min is not anything I am seeing. Very rarely close to midnight a short bump to stage 2. How do you know what algorithm nest uses ? I doubt it is the high limit switch or the system would lock out. I agree it's oversized. The coal furnace comment is unfounded.

As I said in my initial post I am going back to the installer so am fact finding here. Repeating that same comment is not useful to information gathering.

[jtrammel]

Robo comes off as Mr. Know it all sometimes and he is wrong on occasion. Your two stage furnace with a 2 stage stat will only bring 2nd stage on when necessary. As for you being better off with a coal fired furnace, he's probably correct.