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Ask me anything about HVAC heating air conditioning air quality control

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  • Sep 19th, 2017 5:58 pm
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Deal Guru
Mar 23, 2009
13993 posts
2310 upvotes
Toronto
Did a search, did not find it.

Anyone here using a 2-stage / multi-stage air conditioner? I'm curious, do you find it a benefit? Or are we just better with a single-stage AC paired with a multi-stage furnace fan?

So, here is my setup - two furnaces, two air conditioners.

Setup 1) This one had a load calculation done by an HVAC engineer, as required by the city for our building permit. Main floor, 2nd floor, and basement. Total living space 2835 square feet. Estimated volume 25515 cubic feet based on a 9 foot average height. (Lower ceilings in basement, but cathedral ceilings on 2nd floor.)

Cooling requirement is 34983 BTU - Got a Lennox 14ACX-36, which is a 3-ton single-stage AC
Heating requirement is 51057 BTU - Got a Lennox G71MPP-36B-70K, which is a variable stage 26500 to 66000 BTU furnace (70000 BTU input).

Installed about 7 years ago. After updating the ducting, this seems to run reasonably well, with the fan usually a fairly low setting. Does not short cycle in the summer and on the hottest days doesn't need to run all the time. Humidity controlled in the 40%-50% range in the summer IIRC. Also have an HRV, but it doesn't seem to kick in much. I'll have to play with the settings.

Previous to this install, I had a 100000 BTU furnace and a 2.5 ton AC. Supply and return duct sizing was too small and while the place was fine in the winter, the basement ducts going to the 2nd floor got very warm, but by the time it got to the second floor it wasn't so warm, so I guess it was way oversized to overcome the small ducts. Plus it was on full blast when it came on, which was really annoying. Summer was a problem though, with 2nd floor always hot in summer.

While the AC might have been slightly undersized, probably more of the benefit of the new install was the updated duct sizing, correct? Current AC sizing is about 945 square feet per ton, including the basement. Previous AC sizing was about 1134 square feet per ton.

Setup 2) This one was installed before I was smart enough to demand a full HVAC load calculation. This is around 2100-2200 square feet, with no basement, just a 4 foot tall crawl space, and includes a converted garage, with a bedroom over top of it. The two bedrooms have big windows and windowed patio doors, and the main floor is covered in windows and has two sets of windowed patio doors. In other words, the main floor is almost like a green house on two sides. Guy originally came in and spec'd a 2.5-3 ton AC unit, but then came back one day all worried and insisted we up the tonnage to 3.5 ton. I was thinking that by a rule of thumb estimate, a 2.5 ton would have been OK but he convinced me that due to all the windows and doors, 3.5 ton would be safer. Cost premium was not much at all, so I believed him and had the 3.5 ton installed.

Furnace is pre-existing 60000 BTU Carrier 58MCA060-12, single-stage I believe, with 56000 BTU output.
AC is 3.5 American Standard / Trane 4A7A4042B1000AA 3.5 ton single stage.

Furnace installed probably about 15 years ago. AC installed 9 years ago.

The second setup is actually in a later build with somewhat better insulation, but the windows and doors are a significant source of loss. The ducting to the main floor and main second floor bedroom is probably fine but the ducting to the converted garage and the bedroom on top of it is not. Plus I'm not sure how good the insulation is there. In the winter the converted garage was always cold, so I installed electrical baseboard heating for on-demand heating. In the summer the garage is perfect, but the bedroom above it is often very warm, so I got a window AC unit for it (although so far I haven't used it).

I'm thinking the AC unit here is oversized especially considering the converted garage doesn't get adequate air flow, but interestingly the AC doesn't seem short cycle either, even though the furnace is single-stage (I think). (It doesn't run as long as setup #1, but setup #1 has a variable stage fan.) The humidity is in the acceptable range. On the hottest days it's in <50% range, and although I've noticed IIRC the humidity can hit the low 50%+ range on an humid day when it's cooler outside and the room doesn't need as much cooling. So, while the humidity seems to be in the acceptable <55% range in the summer (with rooms cooled to 22C to 23C), it does seem the humidity does run a little bit higher than setup #1.

Nonetheless it's comfortable. I like 45-50% humidity the best it seems. Would a 2-stage AC + 2-stage furnace be best in this context? Or would a 2-stage / multi-stage furnace with single-stage AC be sufficient, like setup #1? Judging by my results, I'm thinking 2-stage 2.5-3 ton AC might work best in setup #2 (although I would lean heavily to just getting a load calculation done by an HVAC engineer).

Cost premium of 2-stage AC units is a consideration, but not a huge concern.

I know it's early since my AC is only 9 years old, but nonetheless I've been thinking about this, and want to be prepared should the AC and/or furnace conk out one day. I'm thinking the furnace may die first as it is likely 13-15 years old now, so I'd get a multi-stage furnace to replace it, and then at a later date when it comes time to replace the AC, I'd consider a 2-stage.

BTW, do all furnaces have the option to be installed sideways? As mentioned, that has no basement, just a 4-foot tall crawlspace. So the furnace is installed there horizontally.
Member
Sep 9, 2008
406 posts
49 upvotes
Mississauga
Where does one buy mastic sealer? Can't find it any of the box stores, amazon etc...
Deal Addict
Apr 2, 2007
1464 posts
134 upvotes
Looking for an extra filtration add on, ie.) HEPA. Suffer from bad allergies and looking for something that will help improve the quality of air inside. Recommended brands/products- looking for whole house system.
Deal Addict
Feb 24, 2008
2036 posts
600 upvotes
Mississauga
Hello There.

I have a mid efficiency furnace (Lennox Elite Series 75K BTU; approx 20 years old). Currently its vented through the roof and the vents runs right up through one of my kitchen walls. I'm looking to do a kitchen reno which involves removing the wall in question and am wondering if this type of furnace can be vented through the adjacent wall in the basement. I've attached a picture for reference

Image

Image

White box = vent to furnace
Red Box = vent to water heater
Blue Arrow = vent up through the kitchen through the roof

looking to re-vent both water heater and furnace through the wall (left side of window)

Can this be done? Do mid efficiency furnaces allow for venting to go through the wall? If so, any rough ball park idea on costs to do this?

Thanks for your time RFD!
Member
Dec 27, 2007
460 posts
45 upvotes
Aurora
These cant be vented out the wall. In order to remove the exhaust pipe from the wall you would need to get a power vented furnace and water heater. At 20 years old though I would imagine you're due for a furnace soon!

mau_mau wrote:
Aug 3rd, 2017 8:53 pm
Hello There.

I have a mid efficiency furnace (Lennox Elite Series 75K BTU; approx 20 years old). Currently its vented through the roof and the vents runs right up through one of my kitchen walls. I'm looking to do a kitchen reno which involves removing the wall in question and am wondering if this type of furnace can be vented through the adjacent wall in the basement. I've attached a picture for reference

Image

Image

White box = vent to furnace
Red Box = vent to water heater
Blue Arrow = vent up through the kitchen through the roof

looking to re-vent both water heater and furnace through the wall (left side of window)

Can this be done? Do mid efficiency furnaces allow for venting to go through the wall? If so, any rough ball park idea on costs to do this?

Thanks for your time RFD!
Deal Addict
Feb 24, 2008
2036 posts
600 upvotes
Mississauga
bonerhaus wrote:
Aug 3rd, 2017 9:00 pm
These cant be vented out the wall. In order to remove the exhaust pipe from the wall you would need to get a power vented furnace and water heater. At 20 years old though I would imagine you're due for a furnace soon!
thanks for the reply; not sure that there is an exhaust pipe in the wall now - why would I need to remove it? sorry, dont know much about this stuff.
The Water Heater is a Rheem Ruud 40 Gal

are you saying these type of water heater/furnaces cannot be vented out through the wall at all?
Member
Dec 27, 2007
460 posts
45 upvotes
Aurora
Sorry if my post was a bit confusing. I was referring to the exhaust pipe going up in your kitchen wall that you want to remove.

Both your furnace and hot water heater use natural draft venting which require a chimney and can't be run sideways out the basement wall. To do that you would need a newer power vented model.
mau_mau wrote:
Aug 3rd, 2017 9:09 pm
thanks for the reply; not sure that there is an exhaust pipe in the wall now - why would I need to remove it? sorry, dont know much about this stuff.
The Water Heater is a Rheem Ruud 40 Gal

are you saying these type of water heater/furnaces cannot be vented out through the wall at all?
Deal Addict
Feb 24, 2008
2036 posts
600 upvotes
Mississauga
bonerhaus wrote:
Aug 3rd, 2017 9:37 pm
Sorry if my post was a bit confusing. I was referring to the exhaust pipe going up in your kitchen wall that you want to remove.

Both your furnace and hot water heater use natural draft venting which require a chimney and can't be run sideways out the basement wall. To do that you would need a newer power vented model.
ok, gotcha now...so I'm looking at potentially replacing both pieces (ugh) as I really want to remove the wall in the kitchen. Based on the pic that i provided, can you comment on the space on the wall near the window? Does it look adequate enough to allow for all venting? There's approx 6 - 7 feet from wall to the furnace
Member
Dec 27, 2007
460 posts
45 upvotes
Aurora
Venting out that wall shouldn't be a problem. Can't guarantee it without actually seeing what's there but I've yet to find a house that I couldn't find an appropriate venting location in.
mau_mau wrote:
Aug 3rd, 2017 9:51 pm
ok, gotcha now...so I'm looking at potentially replacing both pieces (ugh) as I really want to remove the wall in the kitchen. Based on the pic that i provided, can you comment on the space on the wall near the window? Does it look adequate enough to allow for all venting? There's approx 6 - 7 feet from wall to the furnace
Deal Addict
Feb 24, 2008
2036 posts
600 upvotes
Mississauga
bonerhaus wrote:
Aug 3rd, 2017 10:00 pm
Venting out that wall shouldn't be a problem. Can't guarantee it without actually seeing what's there but I've yet to find a house that I couldn't find an appropriate venting location in.
thanks for your feedback - appreciate it
Deal Addict
Dec 19, 2009
2349 posts
823 upvotes
mau_mau wrote:
Aug 3rd, 2017 8:53 pm
Hello There.

I have a mid efficiency furnace (Lennox Elite Series 75K BTU; approx 20 years old). Currently its vented through the roof and the vents runs right up through one of my kitchen walls. I'm looking to do a kitchen reno which involves removing the wall in question and am wondering if this type of furnace can be vented through the adjacent wall in the basement. I've attached a picture for reference

Image

Image

White box = vent to furnace
Red Box = vent to water heater
Blue Arrow = vent up through the kitchen through the roof

looking to re-vent both water heater and furnace through the wall (left side of window)

Can this be done? Do mid efficiency furnaces allow for venting to go through the wall? If so, any rough ball park idea on costs to do this?

Thanks for your time RFD!
They do make separate power ventors for mid-efficient equipment but for a 20 year old furnace it probably wouldn't be worth it.

http://www.tjernlund.com/gassidewall.htm
Newbie
Sep 30, 2008
9 posts
Hi there! We bought a house last fall with Central air, but I'm having issues with the ac. I have an old ac unit that keeps tripping the breaker. I had a guy come to look, but he couldn't even access the unit to look at it (they built a new deck that butted right up to the access panel!)
He suggested from looking at it, that our best bet might be just to get a new unit.
My question is, I found this Kijiji ad: https://www.kijiji.ca/v-hvac-service/gu ... 1283925166 . Are these Kijiji deals reputable? Should I pull the trigger? My house is about 1500 sq ft( including basement)
Thanks!
Deal Guru
User avatar
Feb 8, 2014
13185 posts
3207 upvotes
lyle26 wrote:
Aug 4th, 2017 7:41 am
Hi there! We bought a house last fall with Central air, but I'm having issues with the ac. I have an old ac unit that keeps tripping the breaker. I had a guy come to look, but he couldn't even access the unit to look at it (they built a new deck that butted right up to the access panel!)
He suggested from looking at it, that our best bet might be just to get a new unit.
My question is, I found this Kijiji ad: https://www.kijiji.ca/v-hvac-service/gu ... 1283925166 . Are these Kijiji deals reputable? Should I pull the trigger? My house is about 1500 sq ft( including basement)
Thanks!
Anyone who diagnosis a new unit without checking the current one should not be trusted. Being unable to access it sucks and can prevent diagnosis but it does not prove the only answer is replacement :facepalm:

BTW to replace it you may have to access the old one anyways Face With Tears Of Joy
Lies, damned lies, statistics and alternative facts
Deal Addict
User avatar
Feb 1, 2009
1945 posts
711 upvotes
Toronto
Hi all, just wanted to see if anyone else has this same occurrence. We installed our A/C early May but we have only really started to run it from June - now (so only 3 months really). I went to check something in the basement and noticed there was rust building up on top of my furnace. I took a look and saw water has been seeping out from these pipes slowly and sitting on top of my furnace when the A/C is running.

I know condensation occurs with A/C systems but this seems a bit too much for condensation from the suction pipes. Water has been slowly dripping down on top of the furnace when the A/C is running. It doesn't seem normal as my parent's A/C doesn't do this.

I've already contacted the technician, he says it is most likely condensation but just wanted to get second opinions.
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[OP]
Deal Addict
Dec 27, 2007
1074 posts
113 upvotes
Markham
redkulat wrote:
Aug 14th, 2017 3:14 pm
Hi all, just wanted to see if anyone else has this same occurrence. We installed our A/C early May but we have only really started to run it from June - now (so only 3 months really). I went to check something in the basement and noticed there was rust building up on top of my furnace. I took a look and saw water has been seeping out from these pipes slowly and sitting on top of my furnace when the A/C is running.

I know condensation occurs with A/C systems but this seems a bit too much for condensation from the suction pipes. Water has been slowly dripping down on top of the furnace when the A/C is running. It doesn't seem normal as my parent's A/C doesn't do this.

I've already contacted the technician, he says it is most likely condensation but just wanted to get second opinions.

That amount of water isn't acceptable. It could be caused by air leakage where the pipe enters the metal, or a blocked drain, or an un-properly levelled evaporator coil. You should have someone come and check it out before it causes permanent damage to your furnace.
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