Replace an American Standard VS 80?

[bachampdukes]

I'm replacing my 20 y/o AC unit and was told I should consider replacing my furnace (said American Standard Freedom VS 80 100,000 BTU).

I moved into this 2400 Sq ft 1975 two story last summer. We had gas bills over $300 during the coldest months last winter. I know I have inadequate insulation (which will be remedied this month) leaking duct in the crawl space (which I think I've gotten under control) and a large family room on a cement slab that always seems cold.

The furnace is in the garage, and seems to keep the un-insulated double car garage almost as warm as the house. Is this normal to have this much heat loss at the furnace? Its been about 50 degrees the last few days and the furnace has been kicking on every 10 -15 minutes and running for 4 minutes. Is this an appropriate cycle?

I've had three companies give me a quote. They all seemed thrilled to sell me a new furnace, but not concerned with the system as a whole. None of them did any calculations and just used the numbers off of the old furnace to determine what size I would need. I didn't really think that much about it until I ran into this site a few days ago and have become enlightened.

I expect to get some improvement on the system just from the duct work I've done, and the insulation in the attic. Should I replace the A.S. 80 VS for something new in the 93% AFUE range, or just try to improve the insulation and duct work some more, and ride the old furnace out?

Thanks in advance.

[mark beiser]

Without being able to evaluate the situation, that is a tough call.
In general, replacing a newer 80% furnace with a 90%+ furnace, just for the gas savings, is a very poor investment in most areas.

If the furnace is significantly oversized to begin with, the case for replacing it with a correctly sized condensing furnace is much stronger.

From your description, you likely have duct leakage issues that need to be addressed, especially any leakage in the garage. The garage is the worlds stupidest legal location for a furnace.
Since some moron has already done you the disservice of locating it there, every thing about it needs to be made 100% air tight so absolutely no air whatsoever leaks to or from the garage from the furnace or ductwork. Ideally, look into building a mechanical room around the furnace that is tightly sealed off from the garage, but leave proper service clearances around the furnace.

The bottom line is, you need to find a contractor that will evaluate and TEST the entire system, and do a load calculation on the home.

I've had three companies give me a quote. They all seemed thrilled to sell me a new furnace, but not concerned with the system as a whole. None of them did any calculations and just used the numbers off of the old furnace to determine what size I would need.

Make a pile of all of the quotes from those companies, pick them up, walk over to the trash can and drop them into it.

Sounds like they are all just playing the BID game.
BID is short for Beat Idiots Deal.

[beenthere]

As Mark said, if you can get a company to do a load calc, and a 80,000 btu 90% or smaller furnace will handle the heat load, it might be worth it.

Do all the insulation and envolope improvements you can to your house first. Then either find a company to do a load calc, or click on the HVAC CALC link, and do your own.

The short cycling your experiencing could also be from your thermostat. Many companies don't check this, since they don't make as much on a thermostat, as they do on a new furnace.
Its sad, but some companies are just about the buck.

[BaldLoonie]

1. Where are you and what are your electric rates?

2. Do you have a 2 stage stat?

[bachampdukes]

Thanks for the feedback guys - much appreciated.

I'm in Oregon; gas was $1.34/therm on my last bill. Is that good or bad compared to the national average?

As far as I know, my thermostat is not a two stage. I didn't even know there were two stage thermostats It's just a $60 honeywell from the Depot I got because I thought I was being super efficient by doing 7 day programming - Ha! - little did I know.

I've really dug into my duct work and I'm so pissed at what I've found. I can't believe the hack job that was done on this install. Things like reductions from 8" to 6" by cutting ears on the 8" and bending them down around the 6" pipe, holding it together with a few screws, and covering it up with insulation so is wasn't visible - no tape or anything to try and seal it. I should post pictures for your entertainment. I'm fixing as I go.

I guess the big issue for the furnace replacement is that the existing coil has to be replaced for the new AC unit I'll have installed. The line of thought is the labor involved in pulling out the existing furnace to put in a the taller coil is about the same as installing a new furnace. So by installing a new furnace now, I'll be saving the labor, and only adding the cost of the actual furnace.

The guy who looked at it yesterday -who was light years ahead of the previous three and who I'll most likely go with when I make my choice- said he figured the materials to labor ratio would be about 60/40.

He suggested an air scoop in the duct, and two dampers as the simplest way to manage some of the cold areas in the house. Zoning was another alternative, but I'm sure that is more money than I want to spend. I'm assuming that zoning must cause the furnace to cycle more frequently to accommodate different zones and thus making the system less efficient? Is this another negative factor in zoning?

Thanks Again

Brian

[The Penguin]

No matter what you do unless you do what mark says you will be wasting massive amounts of energy loosing cool air in the summer and warm air in the winter.

I would have the duct work sorted out to improve air flow to reduce restrictions, losses etc as well as enclosing the furnace off of the garage

adding insulation to your attic is good as well

In my opinion what I would do in addition to fixing up the ducting and enclosing the furnace is to keep the existing furnace if its safe and put in a heat pump with the furnace with an outdoor sensor and honeywell vision pro 8000 to provide change over when its really cold or the heat pump is in defrost using 410A system you would be unlikely to use the furnace for most of the winter. the pay back would be pretty reasonable given you are already paying for a/c and the install of a heat pump is labour wise not a whole lot more so you are just looking at the extra parts cost for the most part


I have a R22 heat pump with oil backup and the oil only comes on in defrost and for about a week of nights when it gets below -9°C over the whole yr

I would think you could use R410A down to -11° or 13° without any problems

[BaldLoonie]

Those are high gas rates. I'd look into an add on heat pump. In your climate, you'd rarely need backup just like Penguin says. I'd bet you'd save a bundle.

I hate to see you throw out such a nice furnace. I have one too, it's not going anywhere unless someone gives me a new one. How tall is your coil box? What size unit do you need? There are shorter coils available.

[tigerdunes]

bachampdukes

Several questions.

1.What size is the existing AC condenser that you are replacing?
2.What is your electric rate?
3.How old is your existing Freedom 80 var speed furnace?

I second Baldloonie's suggestion. I would not replace your furnace.
Find a qualified AmStd dealer experienced in dual fuel and add an AmStd heat pump.
Also, get rid of that cheap thermostat and add something decent like the Honeywell Vision Pro IAQ.
I would also have your ductwork thoroughly inspected for size,supply/returns, leakages, insulation qualities, overall condition, and now would be the time to address any hot/cold spots in your home related to airflow issues.

Do you have a good whole house media cabinet? If not consider adding one.

IMO

[bachampdukes]

Thanks for the replys everybody; sorry for my delay.

Tiger,
Existing AC is 3T
Existing furnace is +/- 10 years old
Electric rate is around 8.7 cents.


Since my last post, I've decided to have the current furnace serviced, have some manual damper additions, an air scoop put in the box, and duct re-worked – all by a fourth company I’ve found. I've opted to hold off on replacing the A/C until the spring to give me time to play with the furnace and duct before committing to replacing anything else. I talked for nearly three hours with their estimator from company #4 about possible solutions, how they tuned the furnace, and how the work would be done.

So I hurried home today to catch the techs before they finished the job.

They had opted not to re-work the duct work going to the cold area of the house that had been part of the job quote - "there's nothing wrong with it", the tech said.

They installed two manual dampers on the supply lines, one to the cold area of the house to be closed (partially) in the summer, and one to the upstairs to be closed (partially) during the winter. They also did the scoop in the box intended to divert air into the duct for the cold area.

I checked the results: Leaving the dampers open, and just checking the performance of the scoop resulted in no change to air movement from before they began. Closing the upstairs damper to 75% resulted in minor improvements to the cold area in rear of the first floor (cold area), major air flow increase to the front of the downstairs (which I didn't want to change), and a vibration in the supply lines off of the furnace.

The estimator had been very clear about the use of a combustion analyzer (CA) in the tuning of the furnace. The tech who did the work today said there was no use for a CA on this furnace (said AS VS 80) "because they could not change the oxygen in the burner." So I asked, can’t you change the gas level which still changes the combustion rate? He said he checked the water column and it was 1.5" in 1st stage and 3.5" in second. He also said he checked the temperature rise between first and second stage, but had to pull the cover off the furnace and read the manufacturers sticker to tell me what that was.

1) Does the "no point in using a combustion analyzer on this furnace" fly?
2) How much of an issue is the vibration due to dampers?
3) do scoops in the box ever really work?

Thanks again.

[mayguy]

What is the model of your t-stat? It just may be a two stage stat, and you were not aware of it.

[bachampdukes]

Existing Theromstat is a Honeywell RTH6300; like I said, a Depot cheapy-I confirmed it is not two stage.

Follow-Up Question: What should a H.O. expect when their furnace is serviced?

Is using water column sufficeint for gaging combustion, or should a combustion analyzer be used?

[beenthere]

Water column only tells you the pressure of the gas. Not how well it is burning.
So yes, an analyzer should be used.