HVAC system upgrade questions

[Learninggal]

Sorry for the long post but I need advice on my planned upgrade this spring. Would appreciate some folks chiming in here

• NYC / Climate Zone 4, 2200sq feet home (approx 1500sq feet on 1st floor, 700sq feet on 2nd floor and finished basement not included in this total number but it's 600sq feet). I divided the staircase from 1st to 2nd floor equally in each floor's area. Leaky home but I have replaced all three entry doors and will be doing blown-in insulation in basement rim joists along with attic. All the stucco walls in the house will remain uninsulated and our double pane windows are older. We have ripped out the basement drywall so we can insulate and control humidity during the summer time
• Two systems single-zoned each. Basement/1st floor unit was upgraded from a 20 year old 100K BTU to Bosch 96% 20 SEER 60k BTU/3 ton a-coil and I’m trying to upgrade the attic unit that serves the 2nd floor. It’s currently also a 100k BTU unit
• In the winter time it's mostly the first floor unit that is operational all day long since heat moves up and the second floor unit comes on only during the coldest days (we typically like 70 during day, 66 at night). In the summertime I would think the units would be operational equally given we plan to use air conditioning with the new system (didn’t in the past as it unit would cycle too often and make us feel cold & hot)
• I think second floor will do fine with 30K BTU but those are pretty uncommon. I do see 1-2 of these models but wondering if I should go for the more common 40K BTU which come in a kit (furnace, a-coil, condenser). My other thought is to simply duplicate the 1st floor bosch unit exactly so I can exchange parts between the two units if one fails on the fly and don’t have to wait 3-4 days to order parts. If you folks have some models in mind and what SEER I should target, please suggest but I usually prefer higher upfront equipment costs and buying more efficient equipment and then recuperating on lower monthly cost because energy prices in New York City continue to go up aggressively
• I also need fresh air intake because I did some basic testing with an HVAC engineer which showed negative air pressure at home (tissue paper test through door/window crack while turning on all exhaust fans. No blower door test yet). The test showed negative pressure is greater on the 1st and 2nd floor and less in the basement. I suffer from pollen allergies for eight weeks of the year in April and May. Keep in mind that anything I purchase for this purpose will most likely only be operational for eight weeks of the year. I guess placing this unit in the basement is better versus second floor which could risk a water leak into the living area change filters can be a pain in attic though I do that for the current HVAC unit currently
• I already have a thermastor compact 70 model in the basement for dehumidification which supposedly can be equipped with a supply duct kit, return kit, external filter housing with merv 14 return kit to bring fresh filtered air in. Or perhaps, I can invest in a new ULTRA-AIR 70H or 120H. I have been told to create an independent return and connect the supply to the main supply duct of my current HVAC unit. I've also been told that either of these units are powerful enough to blow air through my HVAC system even if it is not turned on. Do you guys know if the thermastor unit has the ability to turn off fresh air and simply keep the dehumidification function turned on. Or do I have to manually disconnect the fresh air or close off some damper going to the outside wall
• Another alternate is the Field controls FAD-6 or the Fantech AEV 1000 but I guess the Thermastor wins given it has the dehumidifiation function

Thank you

 

[justinjoyal]

Did the HVAC engineer provide you with a load calculation for the house ?

Without one there is no way to determine your needs.

 

[Learninggal]

I didn't get one done because there are so many variables with current insulation and future improvements. Plus I'm at the lowest denominator anyways for my heating/cooling needs on the 2nd floor. Do you guys think a 30k or 40k BTU is a big difference given both can modulate down with a 2-stage furnace and variable a-coil/blower. Thanks

 

[justinjoyal]

I didn't get one done because there are so many variables with current insulation and future improvements. Plus I'm at the lowest denominator anyways for my heating/cooling needs on the 2nd floor. Do you guys think a 30k or 40k BTU is a big difference given both can modulate down with a 2-stage furnace and variable a-coil/blower. Thanks

You need a load calc.

Do you already have supply and return ducts ?

 

[Learninggal]

HVAC system has central air ducts. Basement unit serves itself and 1st floor while attic unit serves 2nd floor

 

[justinjoyal]

And what tonnage are the ducts sized for ?

 

[PoorUB]

I can not see the house from here but 700 square feet upstairs? 40,000 BTU should easily heat it. If it doesn't I would be surprised. I assume it is too large if anything. But as the others say a load calc would be best.

 

[Learninggal]

Not sure what the duct work is sized for but it was supporting 100k BTU in the past. If it supported 100k BTU, wouldn't it automatically support a lower BTU?

Does the furnace BTU dictate what the a-coil tonnage would be or that's completely independent (it could be 1 ton or 2 ton depends on what I purchase). Thanks

 

[PoorUB]

Not sure what the duct work is sized for but it was supporting 100k BTU in the past. If it supported 100k BTU, wouldn't it automatically support a lower BTU?

Does the furnace BTU dictate what the a-coil tonnage would be or that's completely independent (it could be 1 ton or 2 ton depends on what I purchase). Thanks

I seriously doubt the duct work was sized for the 100K. It might have been, but my guess is some hack tossed in the 100k without verifying he ductwork! How many registers are there on that system, it would give some idea of the capacity.

As for the AC matching the furnace, you can not put a huge AC on a smaller furnace, or a small AC on a large furnace, but a 40,000 should handle 2 tons, maybe 3 tons.

 

[Learninggal]

Attic unit has 3 registers for bedrooms + 2 for bathrooms. One very big return in the 2nd floor hallway

Current 2nd floor units:
Luxaire Unitary Model G8C10016MUC12H Serial W0H6807785 - 100k input/80k output
A-Coil - MC36C2AH1A Serial# A0L6074298
Outdoor condenser Goodman Model GSC130241FD 2 ton 13 seer (22 refrigerant)

It does feel it cycles too often in the summer (6 mins on, 1 mins off) so we have to take off our sheets and put them back on (humidity literally remains unchanged). If 2 tons was too much, maybe all I need is a 1.5 tons or perhaps 2 tons with variable speed will do better since I'm guessing my current units are single speed. Also I'm not concerned about having a lower BTU furnace given the current 100k barely turns on in the winter (the heat from the 1st floor moves up)

Thanks

 

[justinjoyal]

Unless you get a load calc you will only be guessing and that’s hardly ever a good thing.

I know that’s probably not the answer you are looking for but it’s the only one that makes sense IMO.

 

[Learninggal]

A private person I found wants to do the NYC 2020 code report and he said that'll include load for the home and duct design . Is that recommended or should I ask for Manual J & D

 

[67CarGuy]

Attic unit has 3 registers for bedrooms + 2 for bathrooms. One very big return in the 2nd floor hallway

It does feel it cycles too often in the summer (6 mins on, 1 mins off) so we have to take off our sheets and put them back on (humidity literally remains unchanged). If 2 tons was too much, maybe all I need is a 1.5 tons or perhaps 2 tons with variable speed will do better since I'm guessing my current units are single speed. Also I'm not concerned about having a lower BTU furnace given the current 100k barely turns on in the winter (the heat from the 1st floor moves up)

Thanks

Your upstairs unit is way oversized, which is why it's short cycling (on for 6, off for 1). It sounds like it doesn't have a separate dehumidification mode, so the thermostat calls for it to cool, it comes on and drops the air temp without having any real impact on the humidity, then shuts off. Rinse and repeat. A smaller unit will run longer, allowing it to pull the moisture out of the air.

You mentioned adding blown-in insulation in your rim joists? Your rim joists should be air sealed before any insulation is added - at the very least use canned spray foam to "picture frame" each joist bay, before adding insulation. At best, have spray foam installed - this will act as both an air barrier and an insulator, and you'll likely never have to deal with it again. It should also help with your allergies, as you're reducing the amount of infiltration.

If you're replacing your air handlers, look into adding an energy recovery ventilator (ERV). They should be sized for the loads your house has and the duct system(s), which is another reason to get the load calcs done.

Keep asking questions, there's a wealth of knowledge in the membership here, and it's all free for the asking!

 

[Learninggal]

I agree with your spray foam before insulation and that's the plan
I'm already planning to outfit my Santa Fe Compact 70 with supply & return ducts to bring in filtered fresh air into the house. Do I still need to use the ERV?

I did the duct sketch - posting it soon here

Thanks

 

[Learninggal]

R'duct is rigid and F'duct is flexible. Cir is circumference All my width measurements are on the outside and all ducts were insulated 2 years ago so you would have to deduct the insulation thickness to get the actual duct thickness. I guess one change I can do is change duct flexible to rigid for MBR (right side of diagram) since it's an easy change and this is the room that's furthest away from unit. Any other changes you'd recommend? And would you care to recommend any particular furnace/a-coil size with this new information? I haven't started on loadcalc.net yet


Room dimensions:

Room

Length

Depth

Area

Ceiling Height

Master Bedroom	21	12	252​	8
Small bedroom	14	11	154​	8
Large bedroom	14	14	196​	8

 

[Yankeefarmer]

If a unit is running for 6 minutes, then off for one, it is running for 6 minutes out of every 7, or 85% of the time. That does not suggest that it is “way oversized.” I also do not understand what you mean by having to take the sheets off and put them back on. Are you only running the upstairs AC at bedtime? What do you use for temperature setpoints in air conditioning season?

 

[Learninggal]

The air conditioning comes on for 7-8 minutes then off for about 5 mins. And when it comes on it makes it too cold too quick but it’s the damp kind of cold. At night we keep the downstairs unit turned off in the summer and the upstairs unit is set to 72. I did set it to 70 in the past as an experiment but it was still cycling pretty often and did not make us comfortable

I know a-coil and condensers are only one stage but does the variable fan motor help if I get a newer system

thanks

 

[Yankeefarmer]

Before spending money replacing a system that functions, I would spend some time experimenting with operating schemes. If you shut off the downstairs system at night during summer, the humidity down there will increase and spread quickly upstairs. Have you tried leaving both systems running with a set point of 74 or 75? Our great room is actually quite comfortable at 78 because the system removes the humidity. We used to keep the office area of the instrument lab I managed at 74 in the summer and it was very comfortable.

You might also look at whether the bedroom register is blowing on the bed and that is causing the comfort issue.

 

[Learninggal]

Ok, I can certainly experiment with this in July when it gets hot. However my attic system is 20 years old at this point and it has given some issues. I am also planning blown in insulation in the attic and wanted to complete all upgrades before I do that. It’s also using the old coolant. It also has a 100 K furnace which for sure is very oversized. Do you think these are reasons enough for an upgrade? How long do these units typically last before the maintenance on them becomes cost prohibitive. My cost for a bundle comprising of 96% 13 SEER 1.5 ton a-cool, condenser an 40k furnace is $3000 and installation will be 4000

 

[Yankeefarmer]

Ok, I can certainly experiment with this in July when it gets hot. However my attic system is 20 years old at this point and it has given some issues. I am also planning blown in insulation in the attic and wanted to complete all upgrades before I do that. It’s also using the old coolant. It also has a 100 K furnace which for sure is very oversized. Do you think these are reasons enough for an upgrade? How long do these units typically last before the maintenance on them becomes cost prohibitive. My cost for a bundle comprising of 96% 13 SEER 1.5 ton a-cool, condenser an 40k furnace is $3000 and installation will be 4000

It’s all about what’s important to you. Some people want to replace their car every few years, others of us drive 15-20 year old cars without a second thought. There’s another thread here where people are talking about not replacing systems “just because.” Only you can answer the question of whether there is enough reason for an upgrade. I come at it from the perspective of a cheap Yankee. It does sound like you could benefit from a smaller system with lower airflow, but it may be possible to run your existing system at lower airflow. The tough part is likely finding an HVAC professional interested in tuning a system.

After my last post, it occurred to me that I should have also asked about the location of the thermostat for the upstairs unit. If it’s in a hard-to-cool hallway or west facing room and there’s to much airflow to your bedroom, the bedroom will be over cooled and uncomfortable.

I should add that I have never worked in the HVAC industry. I am just a retired licensed engineer who worked and taught in the power industry. I have designed, installed, and tuned equipment in my own old, rambling home and in my workshops, so my advice is only worth what you are paying for it.

 

[Learninggal]

I hear you and enjoy your perspective. Every time I have had HVAC trouble it costs me 500 to 700 to fix. Basement and attic units are completely separate so the attic unit thermostat is on the 2nd floor hallway

 

[Learninggal]

Any comments on my duct drawing?

 

[u3b3rg33k]

@Learninggal, If you want to stick with a ducted system, and intend on replacing the ODU, I would strongly suggest, at minimum you get a 2 stage unit. A lot of the higher SEER/HSPF AC/heat pumps are now inverter models, and that allows you to do things like set the airflow lower without causing coil icing or wasting power.
I just got a "2 stage" inverter unit installed at work, and paired it with a Honeywell prestige IAQ thermostat.

Since it's a factory, we also have the problem of exhaust fans = negative pressure. for fresh air, I just bought a honeywell JADE economizer with non-communicating DCA. I will be using the exhaust fan to trigger the "occupancy" input, which will open the outside air damper (which I'm working on installing, 16" ductwork) and allow fresh air into the return (which will be tempered by the rest of the return air, and then the A coil).

You may want to consider this. fresh air is good, and your exhaust fans will work better when not choked off.
also, since it's an economizer, it watches outside air temp and humidity, and if it's nice enough out, will use outside air as "AC" instead of running the compressor (savings!). of course, you'll need some way to let air OUT of the house, like another damper or large, quiet exhaust fan.

The advantage of multistage equipment is two-fold.
the primary benefits are longer run times, and in AC mode, the latter gives you better dehumidification (and less noise).
the other benefit is more even temperature, because it's not bouncing off the setpoint as much.

"2 stage"+inverter gets you capacity management as well. the ouside unit will ramp up the compressor if the load is higher, at the same airflow. that load may be thermal OR it may be latent heat. so it will automatically work harder if the humidity is higher, since it's goal is a specific coil temp.

 

[Yankeefarmer]

Any comments on my duct drawing?

Only that, with the only return grille in the hallway, the upstairs thermostat is always seeing the warmest air, again suggesting you might be more comfortable in summer with a higher temp setting, since the MBR is always getting the coldest air. Also, you should be leaving doors to baths and other bedrooms open if you are over chilled in MBR.

 

[u3b3rg33k]

I hear you and enjoy your perspective. Every time I have had HVAC trouble it costs me 500 to 700 to fix. Basement and attic units are completely separate so the attic unit thermostat is on the 2nd floor hallway

Only that, with the only return grille in the hallway, the upstairs thermostat is always seeing the warmest air, again suggesting you might be more comfortable in summer with a higher temp setting, since the MBR is always getting the coldest air. Also, you should be leaving doors to baths and other bedrooms open if you are over chilled in MBR.

Multiple T-stats out there have remote sensors, and you can choose to use the remote sensor only, or average the sensors.

 

[danski0224]

Did the HVAC engineer provide you with a load calculation for the house ?

Without one there is no way to determine your needs.

Ha.

No one here wants to actually pay a professional to size HVAC equipment properly... or figure out the ductwork.

 

[justinjoyal]

Ha.

No one here wants to actually pay a professional to size HVAC equipment properly... or figure out the ductwork.

Well, as long as they don't come complaining about how their system does not work properly or how uncomfortable the house is, ok then.

 

[yeldogt]

Are you saying that the downstairs is now a 3T heat pump w/ a furnace ...? The Bosch should modulate when in AC.

When humidity is a concern it's very important to not oversize and one should always think about getting the better equipment -- variable speed equipment is much better at removing humidity and can often be so good that there is no longer a reason for the dehumidifier.

Your equipment is indeed oversized ... is the attic unit in an insulated area ?

 

[Learninggal]

Attic unit is in insulated and we don’t use it or go there unless we have to change air filters. I am still getting options for form salad insulation on the Raptors or cellulite insulation on the attic floor

the Bosch unit is 3 tons but what do you mean set to A

thx

 

[PoorUB]

Any comments on my duct drawing?

With your circumference measurements plus insulation it suggests 6" and maybe 8" duct. I would guess the duct layout is good for 1-1/2 tons, maybe 2 tons. Certainly not good for 100,000 BTU of heat! On the heat side you are got for 50,000, maybe 60,000 BTU.

 

[Learninggal]

That’s the direction I was planning to go in - a 1.5 ton a-coil. Would it be okay to use my current condenser which is only two years old but uses R22 and is 13 seer. I could replace it with a 1.5 condenser for an additional $1000Also I’m not finding higher than 13 SEER in 1.5 tons

 

[PoorUB]

That’s the direction I was planning to go in - a 1.5 ton a-coil. Would it be okay to use my current condenser which is only two years old but uses R22 and is 13 seer. I could replace it with a 1.5 condenser for an additional $1000Also I’m not finding higher than 13 SEER in 1.5 tons

Keep in mind the price of refrigerant. If you need to buy R22 from an HVAC contractor it will most likely be well over $100 a pound. It may be time to go to a higher SEER R410 unit.

 

[yeldogt]

I wanted to say AC

How can it be 2 years old and use r22

What is the ductwork like in the basement ..... Odd that an old house in NYC would have this setup. Was it originally hot water heat ?

700 sf of AC on the second floor ... even with some poor walls my guess a ducted mini would have been great if only AC needed

 

[Learninggal]

Originally it was oil heat from I know. I can’t find any higher SEER 1.5 ton unit. I found this system

And guessing I need a horizontal unit since that’s what I seem to have right now

1.5 Ton 16 SEER Goodman Air Conditioner Variable Speed Split System

The Goodman® GSX16 UP TO 16 SEER Central Air Conditioner uses the environmentally friendly refrigerant R-410A and features energy efficiencies and operating sound levels that are among the best in the heating and air conditioning industry. R-410A is chlorine-free to help prevent damage to the...

hvacdirect.com

if there is another system you’d rather have me consider I’m all ears but higher seer the better since I prefer higher initial upfront capital cost and then paying lower power bills since electricity and gas rates are both going up out here

 

[danski0224]

variable speed equipment

It's also important to mention that variable speed / high efficiency / high "SEER" stuff does NOT work if the ductwork is not installed properly.

 

[u3b3rg33k]

Care to clarify? I'm pretty sure a VS motor or condensing furnace will still spin/burn gas even with crappy ductwork.

 

[yeldogt]

It's also important to mention that variable speed / high efficiency / high "SEER" stuff does NOT work if the ductwork is not installed properly.

One interesting thing about the VS stuff is in some situations it will "fix" bad ductwork .... not leaking and wacky stuff with flex all over the place. But -- there are many houses with undersize ductwork. Modern VS equipment can be zoned very easy ... and by doing so you can often change the main runs in the basement and zone off areas of a house.

You just have to make sure that the smallest zone has a CFM about 25% above the lowest CFM of the equipment. Carriers infinity zoning system is really slick ... it goes through a test of each zone and knows the CFM/ static pressure of the run. When you fire it up it knows what each zone needs and where it has that zones damper. So a hot/ cold second floor can be easily fixed .... same with a great room.

 

[PoorUB]

Care to clarify? I'm pretty sure a VS motor or condensing furnace will still spin/burn gas even with crappy ductwork.

I think the point is some people think the new VS motors will help over come ****** duct work. It might help, just a bit, but crappy duct work is still crappy duct work.

 

[Bert_]

It's also important to mention that variable speed / high efficiency / high "SEER" stuff does NOT work if the ductwork is not installed properly.

It "works" but it won't deliver the rated efficiency.

 

[danski0224]

It "works" but it won't deliver the rated efficiency.

It "works" in the sense that hot or cold air will come out of the registers and the equipment makes noise when it switches on.

The operating costs can increase because that VS motor is trying to deliver whatever it is set for, in that hypothetical crappy duct system.

Then, the repair costs are higher when that hypothetical crappy duct system (or even just the HVAC equipment and filter choices) take out that VS motor due to high amp draw.

The customer is sold on the high efficiency stuff, but then wonders why the utility bills are higher and/or they are uncomfortable after spending buckets of money.