New Furnace - Not what I thought it would be! (Help)

[pgshack]

I just replaced a 20 year old furnace (80% - 100K BTU) with a new 2-Stage (97% - 80K BTU) with variable speed fan.

I don't know if I grew accustomed to the old furnace noises, but the new one to me sounds like jet taking off!

My 2-storey home is 2400 sq ft located in Canada, built in 1975.

The 2nd floor bedrooms furthest from the furnace (basement) have always been colder than the rest of the house by about 4-5 degrees. Now with the new furnace it's 7-10 degrees different.

The supply vents in the living room directly above the furnace blast air, the airflow is more than 3 times greater out of the living room vents than in the cold bedrooms. The temperature in the living room is usually 3-4 degrees warmer than the thermostat setting (set at 70). The thermostat is located in the front foyer (a new ecobee).

The return vents in the partially finished basement is where the bulk of the return air seems to be coming from (about 6 feet away). There are two return vents in the 2nd floor hall (none in the bedrooms) that seem to be barely returning a thing (using the paper test). So air flow/circulation is definitely a concern.

I have closed the dampers to the supply vents on the unfinished side of the basement and the 2nd supply vent to the living room to try to increase air from the upstairs registers, but it has done very little.

The installer has come by once to evaluate the problem and all they did was program Stage 1 to run longer (now runs for 16 mins) and also turned down the max fan speed from 130 to 123.

The house is no more comfortable and furnace still sounds like O'Hare airport.

Any suggestions or advice would be much appreciated

P.

[Adlerberts-Protege]

Did they check static and show the readings?

[kdean1]

Closing registers will make a bad situation worse. The noise is the blower laboring against high resistance. You NEED static pressure measurements.
A load calculation may reveal that the new furnace is bigger than the house actually needs. From your description, the blower is certainly bigger than what the duct system can handle.
Smaller equipment will run LONGER and deliver more heat to the rooms that are cold.

[beenthere]

In first stage, it shouldn't be real loud, but in second stage with under sized duct work, it usually is when you have a VS blower.

You need some duct work alterations, and maybe returns added to those bedrooms.

[pgshack]

Whatever load calculations that were done were basic at best, they only calculated the square footage of the house (that goes for all 4 companies that gave quotes) as far as I can tell.

That being said, my money is sunk into this furnace, so now it is matter of balancing the existing system to minimize the noise and improve the air flow.

1- Is it still worthwhile to check the static pressure?

I can ask the installer to come back and take some readings. Based on the information what adjustments could be made?

2- I will open all the dampers and floor registers

My living room (where we spend a lot of time) was getting uncomfortably warm. The installer also said to keep them all open, but I was dealing with too much air flow in some rooms and not enough in others.

3- Changing duct work and adding returns

With most of the duct work enclosed in the walls, I suppose this is easier said than done. I will ask the installer about this, but was hoping for something less 'invasive'.


Is there anything else I should consider?

From my research, 80K BTU for the size of house seemed to make sense.

I suppose its possible that the load calculation would have pointed me to a different sized unit based on other variables? (including my duct work)

We have yet to hit the winter months and I suspect that the furnace will only run longer in stage 2 as it gets colder.

Would having the fan turned down further help any?

If its a resistance issue, are changes to the ductwork the only solution or can the furnace (or existing duct work) be further calibrated?

Thanks for the advice!

[kdean1]

What research showed 80,000 BTU?

If 80K is really needed then the only solution is to upgrade/enlarge the ducts.

Rooms that get too hot point to a distribution problem. Oversized equipment usually heats rooms nearest the equipment best and doesn’t run long enough to heat more distant rooms.

Turning the fan down because of noise may cause the furnace to overheat. Airflow is set for temperature rise, not decibels.

As you are learning, there’s a lot more to home comfort than a new furnace. Thorough contractors consider all the factors and often cost more because they know more and do more.

[beenthere]

First, the thermostat should be controlling staging, not the furnace board.

Checking static now, can tell whether the return, supply, or both need lots of attention/alteration.

Might be able to slow blower more. But has to be at X CFM to stay within manufacturer's allowable temp rise.

At 1230 CFM in second stage, your temp rise is at 58°F. Don't know what the max allowable is on your furnace.

Your old furnace may have only been moving 800 to 950 CFM.

[pgshack]

I looked at a few website that provide charts/tables for houses (bungalow, semi-detached, 2-storey) and they cross that with square footage.

It was guide only and they indicated that the quotes I got (80K BTU) weren't out of line for the size of the house.....I know....not very scientific.

I am definitely learning more than I cared to learned and now realize how easy it is take for granted (when it working right).

Your diagnostic makes sense - a distribution problem.

I will reach out to my installer about the static pressure test and point out the distribution problem.

I will ask about a load calculations.....I suspect he's not going to like all my questions.

Thanks

I welcome any further ideas or culprits to my problem. In the end I just want my family to be comfortable and not have my kids waking up to a bedroom that is sub-60 degrees every morning.

[pgshack]

Interesting about the thermostat. I asked the installer about that he said that the control board on the furnace controls the staging.

The info on thermostat seems tell me its always in Stage 1 when it on.

Thanks for the info on what the static will tell me, that's good to know.

Now I'm really curious to see what it points to.

[pacnw]

We do not know model of this unit, correct?
Can the OP please provide that?

To further the air flow discussion, your old furnace had a motor that ran at one air delivery speed for heat(maybe a different for cooling, too). This was a constant.

Your current unit, IF it is a variable speed ECM, is going to do what it can, up to a limiter, to deliver the set CFM by ramping up the speed of the motor. Since you state the new unit is quite loud, imagine blowing into a 2" pipe, a cardboard tube from the paper towel roll, a standard straw and a coffee stir straw all at the same volume. The noise will become more noticeable/louder as the size decreases. Based on the duct size, or tube size, the amount of air being delivered will be quit if sized properly.

I say they sized the furnace to rule of thumb, like you did, but never checked duct size. There is a calculation that should have been done, but a static pressure test WILL tell if the restricted air is on the supply, return or both. Various things could be causing the restriction that are NOT duct related, too.

[Adlerberts-Protege]

Ductless!!

[pgshack]

This is great feedback, thanks for putting it into layman's terms (straw analogy).

I agree that the unit size was based on a 'rule of thumb'. It made sense to me given that the previous furnace was 100K BTU (80%) delivering 80K BTU in Stage 2 and the new one is smaller 80K BTU, but more efficient (96%) delivering similar BTUs in Stage 2 (76,800 BTU).

From what I understand the difference is the size of the blower?

BTW my new unit is a RunTru by Trane (A952V) Variable Speed (80K BTU; 4 Ton)

[BNME8EZ]

As has been said you have all the classic signs of air distribution issues. It sounds like you had them before with the old system. Do you tell the dealers that you had this issue? Did they tell you this was a fix for it? Did they make any improvements in the duct around the furnace to improve air flow?

These can be some tough questions for a layman to answer, and professionals should understand what they need to do to improve conditions in the home. From your description you have too much air to some rooms, not enough in others, and maybe even a thermostat location problem. Some of this can be improved on just by the fitting in the duct work around the furnace, others need some duct renovations to improve. My guess is that they did not use good fittings to adapt the new furnace to the old duct, then when you add the extra air needed for the new style furnace it gets noisy. The thing is if the air flow stayed equal your temp differenced room to room should not have changed which is what makes me skeptical about the adaptors used.

[pgshack]

I did have some temperature differences with the old furnace between the main and 2nd floor, particular the bedrooms furthest from the furnace. The variance has increased (5 degrees) with the new furnace and the noise is new (or at least increased noise).

I spoke to the installer who is first going to put a damper on the run going to the living room (the room with the most noise and heat) to see what kind of impact that will have on pressure and air flow.

He did mention that the design of the runs attached to the plenum are not ideal in that there are runs coming directly off the top of the plenum and the air shoots right up.

They did rebuild the plenum, it was previously very wide (maybe 1.5x as wide as the the width of the furnace). Now it matches the width of the furnace.

I will ask about the fittings, is there any tell-tale signs?

[beenthere]

Putting a damper on that run going to the living room, will have the same effect as you closing it.

[pgshack]

So the installer has put a damper on the run to the living room, he said that it should help with the noise. He acknowledged that the noise and 2nd floor heat differences are separate (yet potentially related) issues.

With the floor register covers I have, even closing them fully there was an awful lot of air and noise still coming through. I suppose now that air and noise are trapped in the basement - or should this increase some pressure in system?

The installer added the damper and added a another wire to the thermostat (Stage 2 wire).

So far the result is more quiet, but that is mostly because the system has yet to kick into Stage 2 heat. Whereas before Stage 1 heat was on a 16 minute timer, now it runs endlessly until the desired heat is met.

He is coming back again today make some further adjustments to improve the heat on the second floor. He seemed reluctant to do a static pressure test because he is convinced that it is not the issue. I wonder if it wouldn't at least confirm that it isn't or better point him toward the cause of my issues?

Thanks for you insights everyone.

[mgenius33]

I find supply filters work well to restrict air while not increasing noise as much. With that said, you need to have the ducting modified or replaced.

[jbhenergy]

I wonder if he is reluctant to measure static because he does not have manometer......

If he doesn’t have a manometer I bet he does t have a combustion analyzer. And if he doesn’t have a CA he never set the burner up to run safe and efficiently.

It takes 7 minutes to measure static. Drill 2 1/4” holes in the furnace stick probes in the 2 holes and read what the manometer says.

He can’t take 7 minutes to rule something out?


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[pgshack]

I will propose the static pressure test again. When I looked at the manual for the furnace it seemed to indicate that there were thresholds for static and temperature rise. Shouldn't these be checked as part of the install to be sure that it conforms to the thresholds?

The idea of the supply filter is a good idea. That way it wouldn't be choking off the supply entirely just to avoid noise.

I mentioned before, but when is it appropriate for the furnace to be running in either Stage 1 or Stage 2? (On a 15 degree day)

Should it try to run in Stage 1 for as long as it can to recover the lost temp (up to a point) and then if it can't, it triggers Stage 2?

[BNME8EZ]

I will get yelled at for this but properly installed insulated to x will quiet the noise and will diminish a bit of air flow but not hurt it to bad to that run.