Hi all, I wondering if anyone has any information on venting a furnace to an exterior wall and removing the existing chimney. The house is a 1920's house and I'd like to remove the chimney to add a bathroom. Also, any idea on the cost associated for a job like this would be greatly appreciated. Thanks.
Van
Start at the city hall building permits office. For reasons of fire safety, you probably need a permit to alter any existing furnace chimney.
A chimney has a draft that draws out burnt gas, a non powervent furnace or regular furnace needs the draw of a chimney. Now would be a good time to consider a 94% high efficiency unit that can vent with Pvc, but then what about your water heater, where does it vent.
replace the furnace and hot water tank with the direct vent 90+ types.
this will elminate the need for the chimney and save lots of energy
remember the existing fornace and hot water tank flues exhaust heated air from your home 24 / 7
When I took geometry in the 9th grade, the book had a question that involved calculating the height of a chimney by using congruent triangles, I believe, probably by using the shadow of the chimney to determine the triangles.
It was a story question and started off by saying that a tall chimney drew better.
Norman asked Why.
The teacher (whose name I shall not give) got perturbed, and blustered, and didn't answer him, but a week or two later he brought in a book and made Norman stand at the front of the room and read it. It said that taller chimneys drew better, but it still didn't say why!!! Obviously the teacher didn't know either.
I've got my guess, but I don't know for sure either.
But they do. And I'm sure you can't vent the furnace you have now through an outside wall, unless maybe you built another chimney outside that wall, and even then the greater distance might mean that it didnt' work as well. Maybe if you made it taller it would work as well. I'm sure Norman knows all about this by now.
Updating the furnace (as suggested) needs to be looked at carefully because payback can take a long time. Of course, if the furnace will need replacing in the next few/5 years, replacing can make sense.
My oil-fired boiler has a powervent and vents out the wall, which if it meets code in your area is an option. What I don't like about it, is the noise (maybe a newer one would be quiter than mine), and the fumes do have some smell, and are now distributed near ground level.
You could have a new flue put in on the exterior that takes up a lot less space than the chimney.
If you go forwards with this, you might be able to save a fair bit of money removing the chimney yourself, or contracting that out as a seperate job (after the furnace is plumbed to a different exhaust!).
Dave
Two things to keep in mind.
First, your furnace and hot water heater need to be specifically designed for direct venting. As mentioned in a post above it might be a good time to consider two new high efficiently units (furnace and hot water heater).
Second, you need to be careful as to where the vent exits the house. There are limits as to how close the vent can be to any upstairs windows. Think of the vent gases as washing up the side of the house. You cannot have the vented gasses draft back into the house thru windows above the vent point. You many need to relocate the two new units to another part of the basement to accommodate this very important design criterion.
After those two issues are ironed out, it's just a matter of taking down the chimney brick by brick and covering in the roof, ceilings and floors.
Good Luck.
How much they will save depends entirely on what they have now. To replace an existing 80% furnace and hot water heater that have a lot of life left to try to save money usually isn't going to be cost effective. And going from 80 to 90 hardly qualifies as lots in my book. Sure, if they need a new furnace, then I would go with the 90, but if they just want to remove a chimney for asthetics, this is all gettting very expensive.
Say he is lucky and has an 80% unit, which without proper maintenance and its actual design might be 70-75%. A modern 94.5% unit vs an 80% is a % difference in operating savings of 18% not 14.5%. Factor 18% savings with the true rapid increases in fuel costs that we have had and will continue to see and his now 18% savings becomes greater with every increase in fuel. Add the possibility of his being oversized now and that a properly sized unit will increase efficiency even more by running at the units peak design longer. Add to this that a VSDC blower will easily cut 10-20% off his electric bill winter and summer. Now look at water heaters, Ng tanks loose efficieny every year due to scale, he has options of a higher efficiency tank, or the highest efficency Ng tankless, whick have Energy Factor ratings of 18-25% more than Ng tank. New units could if picked right easily save him 22% more in utilities. In those numbers there is payback, a good investment. It will also raise his houses resale value. Keeping old equipment with present and future utility price projections easily becomes penny foolish when all factors are considered.
Insufficient chimney height (from
Most wood stove manufacturers require a minimum stack height (stovepipe and chimney) of at least 16 feet. Code requires that all woodstove and wood fireplace chimneys must extend at least two feet above any part of the roof within ten feet. Given that topographical and atmospheric conditions can vary considerably from house to house, it is possible for a chimney to comply with these minimum specifications but still fail to extend upward into air of low-enough density to establish ambient updraft. It is not uncommon for fireplaces and stoves in houses that are surrounded by hills or trees, for example, or that are located in the high-density air that often surrounds large bodies of water, to need more chimney height than the minimum required by code.
How are you calculating this? By my calcs, going from an 80% efficiency unit to an 94.5% unit will result in saving 15.4% on energy bills, not 18%. So if his heating bill is $1300 for a season, it would be a savings of $200/yr. That is completely wiped out by the time cost of money, which is to say if he just puts the $4500 he could spend on a new furnace/air in the bank at only 4.5%, he would earn $202 every year. If he has to finance it, it gets a lot worse. The savings on the newer motor would certainly contribute some to this as well, but the biggest other impact would probably be the savings in central air cost, assuming he has that and is replacing a much older, less efficient unit.
I agree that at some point, in can make sense to upgrade. But if the furnace is 80% and still working fine, I seriously doubt you will come out ahead financially, unless you live some place very cold where you will use a lot of energy, etc. And don't forget to factor in that to repair one of these new systems can be very expensive. Replacing that variable speed DC motor or control board is gonna cost a lot more than a simple $100 motor for the furnace he has now.
Factor 18%
The difference of % efficiency gained inbetween two units is calclated by the difference in percentage of the 2 units. Or 80% is 18% different than 94.5%. I had a hard time accepting this till I asked Lennox. So people upgrading to more efficient units really achieve higher percent savings then they usualy realise. Repairs are always an issue, 10 year warrantys are what should always be obtained especialy with VSDC blowers. My numbers show a 6 year payback on a 500$ replacement blower for me, but that is todays Kwh cost, soon I am going up 15-20%. With a
10 yr warranty I am ahead no matter what happens. Another point is how many factor in past Ng price increases to reflect future costs into their payback, there again payback is quicker with a higher efficiency unit.
Well, Lennox doesn't know what they are talking about. Let's say you spent $100 on natural gas. At 80% efficiency, that produced $80 worth of heat, the other $20 was wasted. To produce the exact same $80 worth of heat with a 94.5% furnace requires 80/.945, or $84.6 worth of natural gas. $84.6 X .945= $80. So, instead of spending $100 for gas, you spend $84.6, which is 15.4% less. It's pretty simple and straighforward.
So
I wonder just what the energy savings in $$ is for elminating the chiney flues going with power direct vent is?
2 things theres the cost of the energy used to heat the air being constantly exhausted out the chimneyTheres also the cost of heating the replacement air being sucked indoors to make up the air going up the chimney.
bpth of these must amount to something, on a cold day my chimneys have a good draft even with the furnace or hot water tank disconnected. I noticed that one day inspecting my chimneys.
Just think its like leaving a window open 24 / 7 :(
Trader, I just posted the question of % difference at "The Wall" a place of heating pros, I respect your point but believe in what I said for the present. Stop by there it should be interesting.
Here's another way of looking at it. You put $100 of gas in, with 80% efficiency, you get $80 worth of useful heat out. According to Lennox, by going from 80 to 94.5, you save (94.5-80)/80, or 18.1% in fuel cost. If that's true, then we can buy 18.1% less fuel, which is $81.90. Take $81.90 and put it into the 94.5 furnace and we get
81.9x.945, or $77.40 worth of heat out, which is less than the originalHowever, if you take 15.4% off the 0, you get .6 and put that through 94.5, you get 94.5*84.6, which is
What Lennox is doing is just taking the differences in percent efficiencies, which is mathematically incorrect. But it does give a higher figure, which I'm sure they like :)
replying to vandhna, Iggy wrote: Talk with your HVAC guy or company. Direct Vents or Chimney-less setups are great, but they must meet strict requirements. Like, Direct Vents must be, at least, 3-feet from any operable opening and can't be any closer than 1-foot to any eave (see image). Chimney-less setups that use PVC pipes strapped to the building exterior or buried in the walls become the chimney, but need to meet chimney roof exit requirements and the intake must be goose-necked away from the adjoining exhaust pipe...can be a little ugly or odd looking.
Thanks for the information.
replying to Diesel, Iggy wrote: I'm glad you found it helpful. I really don't know why the information was omitted in the earlier posts, furnace choice is vital but not burning the place down or killing people with carbon monoxide are just as important.
Twit, information was not omitted in earlier posts. You're replying to an ELEVEN YEAR OLD thread. My hope is the dummies from HomeMoaners will someday learn to read, but I have my doubts.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.
