Gas and Oil Home Heating Furnaces - Getting some estimates on replacing furnace, what should I ask them?

Live in a Colonial house in northern Ohio. Gas furnace we currently have is a Lennox and around 40 years old. Tired of $500 dollar gas bills, so we're going to have some contractors come out and give us some quotes on getting it replaced. House sq footage is approximately 1950.

We are willing to consider high efficiency.

Anyone have any tips on what we should ask/know about?

Thanks in advance.

Your current furnace was made in 1969, is this also when your house was built?

Before even thinking of replacing your furnace you need to do a heat loss calculation on your home. There are several programs for doing this available on the Internet but most of them cost a fair piece of money. Here are some links that may help.
HEATLOAD- Heatload Calculator Disclaimer and Login (http://www.heatload.com/html/heatloaddisclaimer.htm)

Home Heat Loss Calculator (http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm)

The Home Energy Saver (http://hes.lbl.gov/)

After you determine the heat loss of your home then you need to assess the potential savings of upgrading the house itself so that it will require less energy to keep warm. This may include simple things like caulking and reducing air infiltration to additional insulation or even new windows and doors. These upgrades should be made before deciding on what size you need for a new furnace.

You may prefer to have the furnace installing company do the calculation but RUN from any installer that wants to size the new furnace from the existing unit.

Ditto on Furds advice.

As an energy auditor I hear your question a lot. Here are some numbers. Your 40 year old gas furnace is still probably about 80% efficient. If you go to a new high efficiency unit they will tell you 93%, but that is the steady state, after it gets going. By the time you figure start and stop conditions, especially if it ends up being too big, you could end up with 85%. But even at 90% that's a 12% improvement (approximately). 12% of your $500 monthly bill would save you $60. Save that each month of the heating season, 6 times $60 equals $360 for the year. That's an optimistic estimate.

Now check out your current insulation, attic, walls, and in the basement. Are your windows 40 or more years old as well? A typical approach would be some insulation and air sealing in the basement. Air sealing all penetrations from basement to house and house to attic. And perhaps some storm windows or temporary plastic covering.

The insulate first approach can give you more savings for a smaller cost and reduce the size of a new furnace when it is eventually installed.

Good Luck
Bud

Thanks for the information!

House was built in 1969....called the furnace vendor and they said the furnace is about 60% efficiency....

Windows are a few years old.....

I'll read through those links posted, and I know we need to insulate some areas better.

I'll add to Bud's statement that your furnace may be 80% efficient. That figure would be combustion efficiency and not system efficiency. The figure of 60% is likely more accurate.

Your ductwork is probably minimally insulated, if at all. If all the ductwork is inside the conditioned space the insulation is irrelevant but if any ductwork runs through UNconditioned spaces such as garage (where my furnace is located) attic or crawlspace then insulation in those areas is important. Equally important is sealing of the seams and any holes in the ductwork. Contrary to its name, common cloth-back "duct" tape is no good for ducts. You need a foil tape as a minimum or a special mastic for ducts to be applied at all seams. Far too many contractors simply don't bother to properly seal ductwork in residential systems.

I agree furd, I just don't want them to play the numbers game and imply a new high efficiency 93% furnace is a whole lot better than your current 60% system. YA know what I mean!!

Many of the upgrades to the system are usually options that can be done with out replacing the furnace.

To compare apples to apples, there might be a service tag on the old furnace to see what its last tune up said for efficiency.

Bud

I agree furd, I just don't want them to play the numbers game and imply a new high efficiency 93% furnace is a whole lot better than your current 60% system. YA know what I mean!!


Hmmm, care to expand on that? I thought 60% efficiency to 90% would be a significant improvement.

Hi David, and that is just what they want you to think:). The 90% is the combustion efficiency and the 60% for your old furnace is probably the system efficiency. Even an old gas furnace will achieve an 80% combustion efficiency, but when you include the delivery system, leaky air ducts, poorly balanced supply and return, and uninsulated ducts, the final heat delivered to your house would be closer to the 60%. BUT the same applies to the new furnace. 90% combustion efficiency, then the system losses with a net delivered to the house of 70%.

Recognize I'm pulling these numbers out of the air, but the principle applies to all heating systems. If you have a service card on your furnace, the tech that tuned it up should have noted the combustion efficiency. That is the number to compare with their 90% number. I wouldn't believe any numbers a salesman comes up with for obvious reasons. Gas simply burns very efficiently so even the old ones easily achieve 80%. If yours really is at 60% combustion efficiency, it should be serviceable to improve that number. And if the system losses listed above, leakage, pressure, and heat loss are happening, then they should be fixed with or with out a new furnace. Then add in all of the house fixes.

I don’t really want to talk you out of a new high efficiency furnace, they will save and if your old one really is at 60% combustion efficiency and can’t be tuned up any better, then the savings are better. But a salesman will tell you what they have prepared for selling points and those don’t always represent the whole story. For example, the 90+% number is WRONG, that only occurs in the steady state after it is warmed up. My display booth was next to a heating companies booth and as we discussed his new on demand 93% gas boiler I asked what the average efficiency was. Note average not steady state. It took some pulling, but he finally admitted that when you average in the lower efficiency during start up it would be closer to 80%. So when a furnace is cycling on and off, its overall efficiency is lower. Too big of a furnace and the more it cycles.

I’ll wrap this up. Do everything you can to reduce your heat loss that is easy, and cost effective, house and heating system. Do or have a heat load calculation done for the improved house. If you feel you made significant improvements, wait on the new furnace to see how next winter goes. If you don’t think the improvements were substantial, then continue with the new heating system. At least it might be a bit smaller and more efficient than just installing one with no improvements.

Sorry for the length
Good luck
Bud

I'll add another comment to the efficiency and dollar savings mix. As the owner of two newer 80% furnaces and having worked with my mother's 90+% efficient furnace, I've found that the cost savings from using less gas are offset by increased maintenance costs. With my own 80% furnaces, I've found I've spent much more in maintenance and repairs than I've saved in gas costs. The days are long gone when the average homeowner could simply change his own filters, oil the blower motor once a year, maybe light the pilot light at the beginning of the heating season, and go merrily about his way. New furnaces need regular maintenance by a pro, and the increased number of computer boards, sensors, induced draft blowers, etc, are that many more components to fail that your 40 year old furnace did not have. Yes we all need to do our part to conserve energy, but don't think there isn't an associated cost with these fuel savings.

Jotted down the serial number from the old furnace, called Lennox. Said it's a G8 model, but they don't have any info on any efficiencies.
Unit listed 137,000 BTU hr input, with bonnett capacity of 109,600 btu hr.

OK, so if I'm not going to get a huge savings in utilities going with a 95% efficient furnace, what efficiency do I settle on?

Doing any sort of cost analysis seems problematic.

I'll add another comment to the efficiency and dollar savings mix. As the owner of two newer 80% furnaces and having worked with my mother's 90+% efficient furnace, I've found that the cost savings from using less gas are offset by increased maintenance costs. With my own 80% furnaces, I've found I've spent much more in maintenance and repairs than I've saved in gas costs. The days are long gone when the average homeowner could simply change his own filters, oil the blower motor once a year, maybe light the pilot light at the beginning of the heating season, and go merrily about his way. New furnaces need regular maintenance by a pro, and the increased number of computer boards, sensors, induced draft blowers, etc, are that many more components to fail that your 40 year old furnace did not have. Yes we all need to do our part to conserve energy, but don't think there isn't an associated cost with these fuel savings.

I hear what you are saying, when one considers the professional coming out to the house. Stories of - over $100 to put in an ignitor, or $500 to put in a new draft inducer, or $800 to put in a new blower motor, etc., definitely might cause a person to reason your way.

However, I started to work on simple furnaces about 23 years ago, and now have acclamated to the high efficiency models. To me, anyway, this work does not quite come up to rocket science. Even though there are more parts, yes - they are quite limited in number, and operational theory is relatively easy to understand. Yet, all the stuff, combined, on a high efficiency furnace, comes no where close to all the stuff to be found, and what can go wrong, on a newer vehicle, for example. And there are shadetree people who have quite the grasp of a lot of what goes on with all those parts.

Today I have diagnsoed problems and replaced the correct parts on almost all the brand furnaces that have cropped up on this forum. With most of these, the operational principles are quite the same, once you know what igniton type you have (usually one of 3 types). Once you understand each ignition type and theory of operation, and if you own a multimeter, and have ability to think things through -----

----well, I can very well see (at least mechanically inclined)homeowner very easily being able to grasp how his/her furnace works if they spend the time to figure out what each part of the furnace does, and why it is there. Understanding the complete sequence, and where all the parts fit into this sequence, is not that hard to understand. As I said, even though the parts are more numerous than they used to be, it is still a very managable number -even if you have to go to each part one by one. Not a car. Not a rocket. Not a human brain, like neurosurgeons have to work on.

A homeowner can save a small fortune in repair costs if he/she just takes some time to try to understand the workings of their furnace. Then once this understanding is had, then also they are more apt to be able to use judgement as to what they could try to fix themselves, or if symptoms preclude them to call in a licensed repair professional to possibly track down something that may affect the safe operation of the furnace.

DIY-ing your own repairs can also be mentally rewarding, and can also make one seem more adept in the eyes of a spouse, even. :D

I'll add another comment to the efficiency and dollar savings mix. As the owner of two newer 80% furnaces and having worked with my mother's 90+% efficient furnace, I've found that the cost savings from using less gas are offset by increased maintenance costs. With my own 80% furnaces, I've found I've spent much more in maintenance and repairs than I've saved in gas costs.



You make a useful point, but it doesn't quiter agree with my experience.


These days, there are typically four levels of efficiency and complexity you can buy: a nominal 80% level, a nominal 90 % level with a single stage condensing furnace, a nominal 90+% level with a two stage condensing furnace and a nominal 90%+ level with a variable input condensing gas furnace.


These days, the single stage condensing gas furnace is the overall best value, in my opinion. These furnaces are typically quite reliable and a good value for the dollar.

The two stage and especially the variable input furnaces have small advantages in terms of increased efficiency, and especially in terms of reduced noise, but they have greater cost and greater complexity that may wind up costing you.

So my bias is towards single stage condensing gas furnaces.

David,

The simpler the replacement furnace, the lower the cost to you, both in purchasing a new installation, and in long term maintenance costs. The secret to replacement is to buy the best quality furnace you can afford. Do some online research before inviting contractors out to bid.

The most important thing to consider in heating efficiency is how much of the heat you are generating is being saved by the house, not lost through inefficient windows, inadequate wall or ceiling insulation, missing or worn out weatherstripping around doors, etc., etc., etc.

Ask the members here what they think of various new equipment brands that are available. And don't forget to visit the public library and check Consumers Reports.

Good luck! :thumbup: