Another Hvac Question...

[Gerritt]

Well... I have decided to replace my furnace. It has been problematic for the last 2 months....not turning off sporadically... and it is worrisome. I have had a couple HVAC guys we work with come and take a look and noone has been able to see anything wrong nor seen it happen... but it does.. the stat is set to 20 i wake up in the middle of the night sweating buckets and the house is at 28... I have changed the stat and the wire going to the furnace... to no avail. Time to bite the bullet and purchase a new one..

 

Now comes the question on which one...

 

I can get a Mid-Efficiency installed for 1750.00 that includes a chimney liner etc... everything it needs to function.

 

Or I can get a High-Efficiency for 2400.00 again everything included...

 

there is an almost 700.00 difference in the two prices. while my cost savings on fuel might be only 5-15 dollars a month...

 

 

is there any other benefits to going to a high efficiency I am missing?

 

is the extra 700.00 really worth it?

 

thanks guys you were a huge help the other night... if I can pester just once more..

 

Gerritt.

[danc]

There's no other benefit besides fuel savings Gerritt. According to your figures, that works out to about 6 years before you break even. High efficiency furnaces are more complicated, which means more to go wrong. For instance they have 3 heat exchangers that could possibly burn out as opposed to one on a mid. If you had a larger house with higher heating costs (meaning more monthly savings), I'd say go with a high. But in your case I'd pocket the extra $650.00 and go with a mid.

[Daplumma]

Where did the 5 to 15 bux a month figure come from?What is the efficiency % of the mid and what is the % of the high?What is the age and efficiency of the old unit?If you are going with the mid one it may be better to spend some bux on the old one if it not completely toast.I assume that this is a gas unit.Depending on the year of the old furnace a runaway furnace should not be too tough an issue to resolve.Might be worth a service call from a good SERVICE mechanic as opposed to a parts changer.If the problem can be duplicated while the mechanic is there he should be able to fix it right away.If you are set on replacing it you may as well upgrade it if you can.

Joe

[ccmtcanada]

I had to think of the same thing when I replaced my furnace a few years ago. I pocketed the cash...the payoff was too long AND the new one was about 30% more efficient than the one I was replacing so I was ahead from that standpoint alone! Noticed a big difference in gas/electric bills after the new furnace went in. Another 5 bucks a month is peanuts...save your cash and spend it on Christmas presents for your family!

[bucktail]

My buddie is a HVAC guy and when I approached him with the same question he said to get the best one you can afford but make sure it has a 2 stage fan in it. Most Mid furnaces don't have it.

It doesnt matter what you have in your basement if it can't push the air to the top floor while its still hot or cool it wont matter what you have.

Thats the problem with my unit. Bottom 2 floors are good and the bedroom is an oven in the summer.

Edited December 9, 2006 by bucktail

[bigfish1965]

Because of the age and draftiness of my house, a mid was all i wanted when I got my new one. Seemed silly to put a high effieceincy unit in a low efficiency house.

[Gerritt]

Where did the 5 to 15 bux a month figure come from?What is the efficiency % of the mid and what is the % of the high?What is the age and efficiency of the old unit?If you are going with the mid one it may be better to spend some bux on the old one if it not completely toast.I assume that this is a gas unit.Depending on the year of the old furnace a runaway furnace should not be too tough an issue to resolve.Might be worth a service call from a good SERVICE mechanic as opposed to a parts changer.If the problem can be duplicated while the mechanic is there he should be able to fix it right away.If you are set on replacing it you may as well upgrade it if you can.

Joe

 

Joe Based upon my monthly heating bills.. there is only a 10% difference between the two units the mid will be 82% and the high would be 92% based on a 100.00 a month bill (mine are never that high) I would save about $10.00

 

the unit I have now is an old Grimsby and was installed in November of 1982 (according to the Techs tag) LOL it even says Grimsby High Efficiency on it... I guess it was a good unit back in the day compared to other standard efficiency models.

 

this thing is huge and requires 3 foot of clearance at either end to open the panels...

 

anyways I have had 2 different techs look at it... people I have known for years and have worked along side on various projects and none of them have ever changed a part on the unit... as they couldnt replicate what it is doing..

 

It is definatly sporadic and only occurs occasionally such as tonight and 3 nights ago...

 

My one buddie Peter (licensed tech) spent 2.5 hours here trying to solve it ( he couldnt get the furnace to fail)

 

But trust me it is failing.... when it runs for 2-3 hours straight fan going at full tilt and the burner is still lit... something is not right...

 

I trust these guys and if they wanted to screw they could have... but didnt... Peter wouldnt even take my money for the time he spent here as he said he didnt fix anything... I know noone else would do that for me.

 

I think I am making the right decision by replacing it... last thing I want is my house burning down when I am not here because I didnt spend 1700.00 to replace a furnace I know is faulty...

 

BTW it is a Payne furnace... made by Carrier... any good?

 

Gerritt.

[Daplumma]

Gerrit,

Do you have the brand and model numbers of the proposed funaces?Might help a bit to help you out here.Dan,you are correct with some of the newer units and the "extra" technology that causes problems.Remember the first "sepentine" heat exchangers with the induced draft motors the Carriers had.They started to fail in the first year because they were very thin and if you had your kitty litter box in the same room the chlorides from the litter would corrode them.As soon as they upped the efficiency by pulling the combustion air from the outside the failure rated dropped dramatically.Pulling the combustoin air from outside will save big bux because you are not replacing the conditioned air that you have burned.If the mid efficiency furnace is using ducted combustion air it may be the way to go.

Joe

[ccmtcanada]

Bucktail has a good point. I did upgrade the blower fan. My heating guy said for the size house I have I only needed a 1/4 horse fan...I insisted on a 1/3 horse so I'd get flow to the upstairs. Make sure you check the ducting after they install it too. My wife noticed TONS of drafts coming out, so we duct taped it all up and it made a huge difference. Good luck!

 

Oh yeah...Gerritt, my furnace stays on the WHOLE time I have a fire going in my fireplace. Other than that, it operates normally. We have been told that because our fireplace is in the basement, the air flow comes from upstairs. The colder air from the higher levels travels by our thermostat and tricks it into thinking it's colder than it really is in the house. Have you ever noticed this happen when you have a fire going? May be worth looking in to.

Edited December 9, 2006 by ccmtcanada

[Gerritt]

Gerrit,

Do you have the brand and model numbers of the proposed funaces?Might help a bit to help you out here.Dan,you are correct with some of the newer units and the "extra" technology that causes problems.Remember the first "sepentine" heat exchangers with the induced draft motors the Carriers had.They started to fail in the first year because they were very thin and if you had your kitty litter box in the same room the chlorides from the litter would corrode them.As soon as they upped the efficiency by pulling the combustion air from the outside the failure rated dropped dramatically.Pulling the combustoin air from outside will save big bux because you are not replacing the conditioned air that you have burned.If the mid efficiency furnace is using ducted combustion air it may be the way to go.

Joe

 

Joe I will be sure to get the model numbers from him at some point this weekend.. I would be interested in reading about its specs etc as well...

 

 

 

Bucktail I live in a bungalow so I should be ok in regards to any blower issues.

 

Rick I am in the same boat... not a ton of insulating value in the house... but there will be when I am done with it

 

 

ccmt I too have a fireplace (NG) in my basement but I havent used it in months.. infact I just dissconnected it as I am tearing out my basement... nows the time to replace the furnace as well with the basement torn out

 

 

Thanks guys, your input is always valuable.

 

Gerritt.

Edited December 9, 2006 by Gerritt

[sirfish]

ccmtcanada, I also had that problem a few years ago , an old hvac guy said to put a cold air return on a wall near the fireplace and when having a fire turn the furnace fan on only. I put one in that I can shut off. This cured the problem and heated the upstairs nicely. In the summer I leave it open and the fan runs continuously on low which circulates the cool air from the basement and the air conditioning rarely comes on. Its worth a shot.

 

It's amazing what the difference in price is from mid to high efficiency considering the wholesale price is only a $100 or so difference. My buddy is in the sheet metal trades and says he can get a mid wholesale for around $900. So the install and markup is incredible. When I sell in the spring I will be calling him to upgrade ,for sure.

[ecmilley]

you might have changed the thermostat but from waht your describing it sounds like a relay is sticking, where the t-stat wires go into the furnace the would be a relay/valve assembly for turning the gas to the main burner off/on sounds like this unit is sticking.

[Rattletrap2]

Gerritt,

Let's start with the "runaway" furnace issue.

If you say the thing keeps running and eventually overheats the house to 28 deg.C, than you have a couple of things to look at. I don't know what you have for a furnace, but if it is an older standing pilot model, it is probably about 60% efficiency, and there is very few items to consider as the cause of your problem. You say that you replaced the thermostat and even the low voltage thermostat wire. Unless you have a relay to control the gas valve (if you do, this could have "welded closed" contacts), then it is most likely that there is something causing the gas valve to hang up occasionally and stay open. If this is the case, it needs to be replaced. A pretty cheap item, but it should be replaced by a licensed gas fitter. Definitely a whole lot cheaper than the new furnace. Any decent fitter should be able to figure this out pretty quick and get you back in operation.

 

The increase in efficiency between this one and the mid-efficient one is as follows:

1)New units are electric ignition. No more standing pilot flame when the unit is not calling for heat.

2)An additional heat exchanger to extract more heat from each cubic meter of gas burned. The flue gases are now reduced to a low enough temperature, that they can be expelled through a PVC vent.

3) Combustion air still comes from within the house on most of these.

Efficiency ratings are probably around 70 to 80%. Pretty good, and as already mentioned, they don't have all the bells and whistles to go bad and result in very expensive repairs. They do have ignition modules, power ventor motors, and air proving switches that can fail. The good old thermocouple and standing pilot are about as reliable as you can get, but they are pretty much(if not completely) extinct now for new units.

 

When you move up to high efficiency, you add the following:

1) Combustion air intake from outside. This saves firing all the nice warm air that you already paid to heat, up the chimney or out the vent.

2) A third heat exchanger to wring even more heat out of the gas being burned. These furnaces will condense the products of combustion back into water. This water is acidic and must be treated (neutralized) before it can go down your drain. Even some models of mid efficiency units can require a drain and neutralizer.

These high efficiency units can be 90+ % efficiency. By the way, electric heat is 100% efficiency because there are absolutely no flue losses or heat exchangers. You just have to weigh the cost of gas over electricity. Gas has traditionally been much cheaper, but these times, they are a changing!

 

If it was me ( and I have a 19 year old conventional gas furnace with a standing pilot), I would evaluate the condition of the existing furnace. If the heat exchanger is still in good shape and not too rusted or starting to show signs of a crack developing, I would fix the problem and run it till it has used up its life. Then I would probably go with the mid efficincy model. Even if I can fix the damn thing, who needs to be worried about it quitting every time you go away in the winter? Just my opinion.

 

Now for your humidifier issues. Get rid of that drum style biological breeding ground! I would never have one in my house again! Get a flow through panel type. Aprilaire is very good and also General Aire and Honeywell make nice ones.

The bypass style can be on either the return or supply plenum. In either case, the warm air plenum is pressurized and the return is in a negative pressure. The air is going to travel from high to low through the bypass duct. It makes no difference. The normal or standard practice is to mount the humidifier on the return plenum and the 6" bypass duct off the supply plenum. In order to evaporate water, you need heat. I prefer to also hook up the water connection to the hot water lines. This will increase the capacity that you get from the humidifier in pounds of moisture per hour. Don't worry about the cost of heating the water, you recover this energy into your system and the water that flows down the drain will be cold. The trick is to make sure that the water is distributed evenly across the top of the mesh panel in just sufficient quantity to be absorbed into the warm air stream. The humidifier has an internal restrictor orifice in the line to reduce water flow. Don't try to do it with the hand valve on the water line.

What you are doing, is distributing the water that flows over the mesh panel and increasing the surface area of each drop of water. As each drop spreads out in a thin layer, it is more readily absorbed by the warm air. Any water that is not absorbed, will flow to the drain. This eliminates the standing sump of warm wetness that grows molds and bacteria. You will have to tee the drain from the humidifier into your condensate drain line from your airconditioning.

 

 

If you had a power style humidifier (no bypass duct) then it would definitely have to be mounted on the warm air supply plenum. They have an internal fan blower that will draw the warm air from the plenum and then discharge it back through the water panel. These work very well also.

 

In either case, the humidistat should be mounted in the living area if possible, usually adjacent to the thermostat. They have models now that will automatically adjust the setpoint as the outdoor temperature changes. They are pretty expensive though, and you have to run more wires for the outside sensor. If this is not pratical to mount in the living space, then the next best place is flush mounted in the return air plenum well upstream of the humidifier itself.

 

The ideal setting would be 35 to 50% relative humidity. Unfortunately as the outside temperature drops lower, the inside temperature of your glass windows, metal door frames, and even poorly insulated walls will drop below the temperature known as the "dewpoint". This is the point where moisture will condense out of the surrounding air onto the colder surface. This can cause fogged up glass and paint damage in your home. In the worst case scenario, we get black mold growth.

 

This is why you have to lower the humidity setpoint as the outdoor air temperature drops. As it gets colder outdide, the furnace runs more frequently and drys the air out. We want to add more moisture, but the dewpoint temperature of those surfaces limit us to what is tolerable without condensation buildup.

 

One last point, your humidifier needs to be interlocked with the fan on your furnace! If the blower is not running, the humidifier needs to be off. To do this on older furnaces, you need a differential air proving switch that will only close its contacts when it senses a difference in pressure between the supply and return plenums.

 

Holy crap, its 2 am!!!!! If I missed anything, let me know! DanC and Daplumma had it pretty much covered anyways before I even got into this long winded typographic diarrhea!!!!

Edited December 9, 2006 by Rattletrap2

[Rattletrap2]

Oh yeah, a wood burning open fireplace can very quickly suck every bit of heated air out of your house and toss it up the flue!!!! Guess where this repalcement of air is going to come from to try to equalize this negative pressure that was created when the heated air left??? You got it, through every crack and crevis in the outer envelope of the home.

 

That is if you are lucky enough to be only inconvenienced with these cold drafts and extended operation of the furnace trying to reheat it!!! If you are not so fortunate to have a leaky poorly sealed house or you have done your bestest to seal everything up tight, you will end up sucking the products of combustion back down the flue or vent from your furnace to make it up. this is where you run into carbon monoxide hazards from the poor or incomplete combustion process in the furnace.

 

Properly burning fuel appliances such as gas fired furnaces don't normally produce CO, but messed up ones do real quick.

 

A good practice is to leave a window cracked open near the fireplace to allow for combustion air to burn the wood and draft up the flue.

My fireplace has glass doors and a vent to outside that feeds right into the fire box. Much better, since we only have a fire because we like the look of it, not for heating. We don't feel any cold drafts with this set-up.

[Fisherman]

Ratletrap2: First, nice write up, second, I also have an older, 1983 standing pilot type gas furnace. You mentioned to look for possible forming cracks in the heat exchanger. Dumba** question, but how do you see them without dismantling the furnace? I can see where the open flame goes up into the exchanger, what about the sides and top? How do you access that area? I clean mine out every year, long brushes similar to barrel brushes for a shotgun, couple of drops of oil for the motor shaft. BTW, I don't have AC or a humidifier on the system if it makes any difference.

Edited December 9, 2006 by Fisherman

[Gerritt]

WOW... that is alot of information!! thanks RT2!!! I was thinking of repairing the old unit... but the wife and I discussed it and decided it is a bandaid measure for a 24 year old furnace and while we have the basement ripped apart now is the time to do it. Otherwise I would be knocking out walls to get the dude outta the basement later..

 

it is about a 60% efficient furnace ( I did the monthly bill method of working it out from CHMC) and there is no chimney liner currently installed (potential for CO2 poisoning)

 

If by replacing the unit I can have piece of mind that I wont have to worry about my house burning down... it is worth it to us..

 

I would have thought furnaces have a trip device to shut the bloody furnace off when it gets too hot.. and by hot i mean the supply plenum is insanely hot to the touch after 3-4 hours of running non-stop.

 

Thank you guys for your suggestions! Helpful as always..

 

This is why OFC is by far the best site on the net.

 

Gerritt.

[Daplumma]

Different brands fail in differant places.Its a good idea to have a carbon monoxide dectector or two around the house.If you have a standing lipot furnace check closely aroung the area where the pilot burns.Many time(but not all)a service tech can tell if there are holes in the exchanger by watching the flames movement when the fan kicks in.I would just make sure you co2 detectors an get the furnace checked every couple of years.

Joe

[steve_paul]

Gerritt, Payne is a decent furnace. It is basically Carrier's generic line but many of the components are the same as you would get on the higher priced Carrier STA model. If you can, check into buying an extended warranty as well for it - lot more parts on new furnaces that can go wrong and they can get expensive.

 

Also, since you are redoing the basement one thing to remember in buying a high vs mid is the combustion air. If you are tightening up the basement and you have a mid, remember to put in some form of fresh air intake to your mechanicals room. The room can run out of oxygen very quickly if both the furnace and water heater are running at the same time and if that happens you can get into a CO problem pretty quickly. You can do this yourself very easily with some 6" insulated flex duct and a dryer hood. As pressure drops in the room when the appliances burn, fresh air from outside is allowed in to equalize pressure and keeps a supply of oxygen in the room to burn.

 

By replacing now, you are getting a chimney liner done. If your water heater goes in the next little while and you don't have a chimney liner, you will need to install the liner before a new heater goes in and depending on who does it for you, that alone can be a 300 - 500 dollar job.

 

Oh yeah, and one last thing - make sure the furnace isn't stolen. If it is a contractor doing it for you there shouldn't be a problem but there is a bit of stolen stuff floating around right now on the market - we came across one a year ago where a "friend of a friend" was able to get someone a furnace for a good deal. Turned out it was a stolen one and the guy who ended up with it was a police detective here. If there is a concern, get me a serial number and I can check for you.

[Gerritt]

Steve, I had my Hot water tank replaced just after we bought the house 5 years ago.. it is a rental unit but hey I didnt have the cash to purchase one.)

 

anyways the gas guy said I needed a chimney liner at 450.00 money I just didnt have having just shelled out 20,000.00 bucks for the house purchase. The tech installed it anyways but made me promise I would get one put in... and to be honest I forgot about it. Till now!! now that I have some bux in the ol' savings account I will be sure everything is done properly and to code.

 

The furnace is coming from a Supply house in Brantford so I am not too worried about it being a stolen unit.. I am going to pick it up in my truck

 

good advice on making sure I have decent airflow in the mechanical room when I am finished renovating,

 

I am leaning towards a Mid-Efficiency unit... can all mids be hooked up to outside air for combustion?and if it is I dont need to worry about CO levels as there is always a fresh supply of O2... and if it is hooked up to the outside does that mean the cold air returns in the house are rendered useless?

 

Gerritt.

Edited December 9, 2006 by Gerritt

[Daplumma]

I am leaning towards a Mid-Efficiency unit... can all mids be hooked up to outside air for combustion?and if it is I dont need to worry about CO levels as there is always a fresh supply of O2... and if it is hooked up to the outside does that mean the cold air returns in the house are rendered useless?

 

Gerritt.

The mid efficiency ususally cannot be hooked up to outside air for combuction unless you put them in a small tight room and vent to the outside.Not recommended unless the designer of the system really knows what he is doing.The combustion air is completely different than the cold air return.The air that the frunace burns goes up and out the chimney.The air that goes thru your ducts never comes in contact with the flames.Sorta like the radiator on your car the coolant(antifreeze) never actually contacts the air that cools it.

Joe

[steve_paul]

Gerritt, don't hook the fresh air intake to the furnace, just run it into your mechanicals room. If you pull -20 degree air over the heat exchanger it will have a very short life. Just run it into the room so when the pressure drops in the room from combustion, air will come into the room to replace it. As Joe said, the cold air returns in the house are just bringing inside air back to be heated (or cooled in the summer), it does not replace the air in the room that has been burned.

 

As Rattletrap said, if the room runs out of oxygen then the appliances start bringing flue gases back down the chimney as the flame is starving for something to burn, leads to imcomplete combustion which leads to CO.

[Rattletrap2]

Sounds like Steve_Paul has a good handle on the current offerings of residential furnaces out there. I had always heard that the Bryant, Payne, Day & Night, and Carrier (all the same, made by Carrier!) were decent furnaces, but since I have never worked in the residential part of the industry, I wouldn't have any first hand experience with them.

 

If you do want to bring in a fresh air duct for combustion air to the furnace room, than I would suggest you install what is called a "saskatoon loop" in the duct. Bring the 6 or 8" pipe into the room, then turn it upwards, and then over and back down. This "inverted trap" will prevent cold air from dropping by gravity into the room. The only time cold air will be drawn into the furnace room, will be when the room goes into a negative pressure.

The negative pressure is created when the furnace is operating and room air is going into the furnace for the combustion process. This happens on conventional and mid efficiency units.

 

Fisherman, if you want to keep a close eye on your older heat exchanger, there are a couple of things you can do.

1) Use a small flexible inspection mirror and flashlight to look up inside the fire side of the heat exchanger. Obviously, you don't want it to be able to fire up during this process!

2) As was already mentioned, sometimes you can see the flames being blown around inside the heat exchanger if air from teh blower is being blown in through cracks.

3) Watch for excessive build-up of loose rust down around the burners. If this is the case, you have a moisture problem and the heat exchanger could be rusting through.

4) Make sure the flames off the burners are going straight up and not wavering around. They should also not impinge against the side walls of the heat exchanger. This intense heat would cause a crack in the metal.

5) Have it checked every year or two by a professional.

 

They now have some pretty cool instruments that make checking the inside of the heat exchanger easier. It is a fiber optic flexible probe that can be up to 5 feet long with small LED lights on the tip. You look through a small viewpiece and you can see right up in there. It will look around corners as well.

Edited December 10, 2006 by Rattletrap2

[Daplumma]

Saskatoon loop..Ilove it.can I use that line?The chances of the entering air into the funace being that low down here are nil to none.Even a short run on the intake on a 90+ furnace will heat up enough that it wont be an issue.Where y'all are at..another story.Maybe we need another forum for hvac theory.I love this stuff.

Joe

[Fisherman]

Thanks Rattletrap2, turn of the 110 to the furnace and for good luck, set it back to pilot before I stick my nose anywhere close to the burners. I'll see what I can check out with the flex mirror.

[John Bacon]

Because of the age and draftiness of my house, a mid was all i wanted when I got my new one. Seemed silly to put a high effieceincy unit in a low efficiency house.

 

I think your logic is backwards. There is more benefit to having an high efficiency furnace in an inefficient house than there is in an efficient house.

 

A poorly insulated drafty house mean higher heating bills; if you furnace is 15% more efficient, then you save 15% of a large bill. The same furnace in a well insulated house still saves you 15% on your heating bill; but it will be 15% of a much smaller number.