Drawing combustion air from elevator shaft?

JUGHNE

I believe the Carrier line and also the Nortek line (furnace families) that are 2 stage, initially light on high fire to establish flame then switch down to the low stage (60% or so).
So the high fire stage still needs the proper venting IMO.

When switching from high to low: the gas valve puts out less gas, the inducer fan is switched to low speed, the big blower is switched down in speed, another set of pressure switches is used in low fire. All these new parts must be controlled by a smarter control board than you have now.
Did he imply just making your existing furnace a 2 stage set up?
Lots of new parts involved for 2 stage burner.

IIWM, I would just put in a new furnace, small enough for the existing venting system.
Or punch thru the roof with 3" piping.

Zman

Has anyone discussed this with the manufacture?

It might work. The entire diagnoses may be incorrect.

They may have a way to downfire the unit without replacing anything.

piluso

He is going to get back to me. He mentioned that intalling a smaller unit, that was my preference at this point, might not be so straight forward. Something about the blower for the AC. He is also investigating this option.

What would happen if I install 3 inch pipe up until the end but do not go outside with a 3 inch pipe. I would prefer to not touch the side of the building.

Thanks

DZoro

Dare I ask. what size is your A/C?

The outside terminations are a good portion of your problem. I'm sure they froze up in the cold spell and that is why you didn't have any heat.
The intake and exhaust pipes must have a minimum separation of 18". The exhaust is to be 18" higher that your intake pipe. It is normally done with two elbows on the outside of the building.
I would not let anyone try do down fire, or attempt to turn that furnace into a 2 stage furnace. Someone (you) could get seriously injured, just not the right thing to do.
I have seen them down fired, and never good results.

Size properly.

piluso

Going back to the diagnosis. The pipe travels 12 feet horizontally with 4 90 angles. According to the manufaturer the limit for a 2 inch pipe is 10 feet. Is it that exact? Could it be something else? The unit runs fine when disconnected from the exhaust pipe. Hence the idea that it is the pipe.

DZoro

You have some vertical pipe there also is that included?

The 4 -90's equal at least 5' per 90= 20' + 12'=32' of pipe.

Over 3x more than spec. Yes it is your exhaust and intake that is wrong. Plus when properly piped you will have another elbow outside.

piluso

Vertical pipe was not included. Looking at those numbers it is the size of the pipe. Thanks

piluso

Thanks for the advise on the terminations. Modifying that is very difficult

piluso

Regarding enlarging the pipe without getting to the terminations. Is that worth trying or should i focus on a smaller unit?

JUGHNE

The roof is not an option??

piluso

I will have to check but i think they are going to tell me to go to the side.

Zman

You are allowed 10' and 2-90's. It sounds like you are over by 12 feet.
I would check with tech support to see if there is a setting that can be changed or a modification to reduce btu's. Don't modify anything without their blessing.

If not, a new furnace is not that expensive. The original installer should throw in the labor for being such a hack.

piluso

The contractor suggested adjusting the gas pressure first. It seems to make sense to me. Would that reduce the BTUs? By how much? any idea? Does it make sense? Many thanks

DZoro

I would not do that, besides it is not your main problem.

The main issue is your 2" vents causing a safety (pressure) switch to open.

Lowering or changing gas pressure will not resolve the issue, just cause other issues like high CO levels, soot and many other bad things.

piluso

Ok, I'm going back to replacing the heater. Thanks.

Brewbeer

Are you working with the original installer, or a new contractor?

piluso

The builder is unresponsive. He came once and also concluded that the pipe was wrong. He said he was going to look into options. This was 3 months ago. So I reached out to a new contractor. I would prefer to work with the original installer, but no luck

piluso

One more question. The contractor thinks that it might be fine to enlarge just the exhaust pipe, but shouldn't I be enlarging both the exhaust and intake?

He found something else related to the return duct which is also small. He thinks I need to fix that too. He thinks that is going to be a problem for the AC unit.

Thanks

Zman

Can you provide details on the duct size and AC unit?
Chances are, if they can't size the vent correctly, they may have messed up that as well.

piluso

Below is his message to me explaining the issue. What about the need to enlarge both pipes not just one? Should they do that?

Thanks


. As I had reviewed with you when I looked at the existing issue. The supply duct coming off the unit is set up for 3 tons of air and the return is set up for 2 tons of air and the condensing unit is a 4-ton unit. We can’t start opening the walls to replace the supply duct without a major mess. I would increase the return, so we can get enough air back to the unit without freezing up due to low suction pressures of the compressor.

Zman

This is like like deja vu all over again.
4 tons of cooling is 48,000 btus. Unless you are using it as a walk in cooler, that sounds big.

piluso

Ridiculous... It is deja vu all over again and very depressing on my side. Oversized stuff that doesn't work!!!

DZoro

You are correct oversize is wrong, too small is wrong also.

Before you do a thing have at least 2-3 contractors give you a heat loss for your condo. Do not share those numbers with any incoming contractor.
You are 1600sqft, just a WAG your sizes should be in the 2-3 ton A/C , Heating between 30,000-60,000. I will probably get some flack for putting up these numbers. But they are in the ball park. Would be on the smaller size given you only have one exterior outside wall, unless your on the corner.

Your system (4T-100,000btu) is way oversized IMO.
D

piluso

Thanks for the advise. The numbers you suggest make sense. It's a 7 year old building. I was certainly not expecting these problems!