90% furnace & combustion air - what gives

[euroboy]

I have a 10 year old Carrier 58MSA series 110 - this is a 90% furnace yet it does not provide for outside combustion air ( of course it is direct vented ). I wonder if anybody has connected it directly to the outside for the combustion air ?

I would be interested to find out what changes took place to allow 90+ furnaces to directly use outside air ?

[acwizard]

I assume you mean a two pipe system. The biggest change was the burner compartment and door, maybe a slightly different inducer fan assembly. Mfgs. like Rheem ,you can pipe the intake or let it draw from the space.

[George2]

I have a 10 year old Carrier 58MSA series 110 - this is a 90% furnace yet it does not provide for outside combustion air ( of course it is direct vented ). I wonder if anybody has connected it directly to the outside for the combustion air ?

I would be interested to find out what changes took place to allow 90+ furnaces to directly use outside air ?

I've sold Bryant/Carrier since 1981. They used to be only a 2-pipe install.

Many of the other manufactures gave the choice (1 or 2 pipes) to the installers. Guess which way they choose?

So, some years ago, (I don't think it's been 10 years already) Carrier gave us the choice. I assume it was something to do with the design, but I don't remember.

[euroboy]

Thanks for the info - by choice do you mean there were two different units and one would order as needed for a given install ?

Looking at the install manual they do not refer to being able to do a 2-pipe setup.

I be interested to find out if there was a retrofit kit, or parts from newer units could be used to make this a 2-pipe setup. What is the main difference between 1 and 2 pipe systems in the furnace design ?

[George2]

Thanks for the info - by choice do you mean there were two different units and one would order as needed for a given install ?

Looking at the install manual they do not refer to being able to do a 2-pipe setup.

I be interested to find out if there was a retrofit kit, or parts from newer units could be used to make this a 2-pipe setup. What is the main difference between 1 and 2 pipe systems in the furnace design ?

It's the same furnace for all manufactures when it comes to deciding on a one or two pipe installation.

The furnace you have will accept a combustion air pipe. The advantage is that it minimizes contamination and makes your home tighter.

Call a qualified Bryant/Carrier dealer and they will (hopefully) know how to do it.

[George2]

Sidebar:

I say hopefully because the largest Carrier dealer in our area installed a furnace and the termination looked like a bull's horn.

The homeowner had to put a piece of plywood between the pipes to keep the furnace going.

I asked the homeowner if they bought the plywood or did he have to?

It was meant as a joke, he didn't think it was funny.

[612Rob]

There are many reasons and advantages to pull the combustion air from outside. Just out of curiosity, why do you want to?

[hearthman]

*direct vent* is two pipes--one in/ one out. A single pipe is a *power vent*.

You should have a two pipe to minimize cold air infiltration and provide reliable MUA and not depressurize the CAZ.

[euroboy]

Currently it is a 1 pipe connection, and I would like to make it 2. The part I don't understand why in the first place the furnace would be installed with 1 - in my case it would take only about 6' of PVC pipe, and with all the benefits of dual connection.

This brings up a question - would a good pro always install as a 2 pipe system ( provided the furnace allowed for it ), or are there valid reasons why only connect the power vent to the outside ?

[acwizard]

*direct vent* is two pipes--one in/ one out. A single pipe is a *power vent*.

You should have a two pipe to minimize cold air infiltration and provide reliable MUA and not depressurize the CAZ.

I do not quite agree with your definition.Direct vent implies that all necessary combustion air is obtained from either an attic, crawl space, or outside via piping directly from one of these areas to the appliance and all flue gases are discharged to the outside atmosphere. Power vent refers to a gas appliance which depends on a mechanical device to provide a positive draft within the venting system.

[acwizard]

Currently it is a 1 pipe connection, and I would like to make it 2. The part I don't understand why in the first place the furnace would be installed with 1 - in my case it would take only about 6' of PVC pipe, and with all the benefits of dual connection.

This brings up a question - would a good pro always install as a 2 pipe system ( provided the furnace allowed for it ), or are there valid reasons why only connect the power vent to the outside ?

To answer your question no, it depends on the conditions which exist for each location. The second pipe is bringing air into the appliance , it is no different than taking air from the space around the appliance if code permits. All gas fired appliances require combustion air to mix with the fuel being burned and to also allow products of combustion to vent to the outside. Mechanical codes allow different scenarios of where to obtain this air from. The only argument in your case may be the possible energy savings from not drawing air from the surrounding space or the infiltration of cold air into the building by not direct venting. The other plus for direct venting is obtaining air which is not contaminated from the outside ,which will help protect the heat exchanger from failure due to any chemicals which may be in the enclosed area. Never store chemicals around a furnace.

[hearthman]

I do not quite agree with your definition.Direct vent implies that all necessary combustion air is obtained from either an attic, crawl space, or outside via piping directly from one of these areas to the appliance and all flue gases are discharged to the outside atmosphere. Power vent refers to a gas appliance which depends on a mechanical device to provide a positive draft within the venting system.

2009 IRC Ch 24 Definitions:
"Direct Vent Appliances-Applainces that are constructed and installed so that all air for combustion is derived directly from the outside atmoshere and all flue gases are discharged directly to the outside atmosphere."

Since we are talking about a 1 0r 2 pipe 90%+ vented with PVC, that makes this a mechanically vented appliance with a positive vent pressure. Therefore, in order to be a *direct vent* an appliance needs a second pipe for intake air from the outdoors as defined by the gas code.

Now, there are *direct vent* appliances that do not power vent because they are a thermosyphoning sealed loop balanced system. However, without the sealed loop and CAT III or IV, it would have to be mechanically or power vented.

Do you still disagree?

[acwizard]

2009 IRC Ch 24 Definitions:
"Direct Vent Appliances-Applainces that are constructed and installed so that all air for combustion is derived directly from the outside atmoshere and all flue gases are discharged directly to the outside atmosphere."

Since we are talking about a 1 0r 2 pipe 90%+ vented with PVC, that makes this a mechanically vented appliance with a positive vent pressure. Therefore, in order to be a *direct vent* an appliance needs a second pipe for intake air from the outdoors as defined by the gas code.

Now, there are *direct vent* appliances that do not power vent because they are a thermosyphoning sealed loop balanced system. However, without the sealed loop and CAT III or IV, it would have to be mechanically or power vented.

Do you still disagree?

I agree with everything about direct vent. But power vent is always forced mechanical draft and should not be confused with induced mechanical draft. There are a lot of people that see an inducer fan in their furnace and believe it is power vented which is not always the case. I know that you know the difference , but most homeowners do not. I am in agreement on CAT III AND CAT IV.

[George2]

Currently it is a 1 pipe connection, and I would like to make it 2. The part I don't understand why in the first place the furnace would be installed with 1 - in my case it would take only about 6' of PVC pipe, and with all the benefits of dual connection.

This brings up a question - would a good pro always install as a 2 pipe system ( provided the furnace allowed for it ), or are there valid reasons why only connect the power vent to the outside ?

No, a professional would always go with a direct (2 pipe) system.

The reason for short cuts is: A) lazy or B) cheap

It's the same reason some use TXVs and others don't.

Some use too small of filters; i.e. 16"x20" drops either to save money or they don't know any better.

[acwizard]

Maybe this attachment might shed some light.

[euroboy]

acwizard - thanks for the document. I still don't understand why the install manual for the Carrier does not even mention dual pipe option - it tells the installer to put a 90 deg. elbow.

I just did a quick search and found the manual for the 58MSA 150 series - in that manual they do talk about using outside air but they refer to an opening in either a wall or foundation to goes to the outside. Series 150 is from 2005 ( as compared to mine from 2000 ) - I am surprised there is nothing in there about 2 pipe option.

Based on the pdf file not only are there benefits of reducing the infiltration, but it suggest the furnace could last longer with 2 pipe setup - do they last longer when dual connected ?

[acwizard]

The furnace would only last longer if the combustion air from within the space was contaminated , like drawing air from a laundry room where bleach might be present. As far as the one elbow that is to insure nothing falls into the combustion area of the furnace, it should be pointed downward.

[euroboy]

I have found the Product Data for my furnace (copy included) - on page two it has the following ( I underlined the part about the combustion air ):

Combustion Air and Venting
— This furnace uses combustion air from an
area adjacent to the furnace and brings
it in through a short section of inlet
pipe that terminates just outside of the
cabinet. The vent pipe can terminate
through a sidewall or through the
roof.

I hope at least one pro has made this furnace a dual-pipe setup, and can comment if there are any issues.

[commerce48]

It says very clearly that it is a one pipe system. The added friction from an outside wall inlet pipe is probably not compatible with operating parameters. Not in the install manual, don't do it!

[hvacvegas]

No, a professional would always go with a direct (2 pipe) system.

The reason for short cuts is: A) lazy or B) cheap

It's the same reason some use TXVs and others don't.


Some professionals go with a single pipe system, because we can't physically run 2 pipes. I've had a few times where I literally couldn't run a two pipe system, and I had to go non-direct vent. I guess that means I'm not a professional :-\

Also, being lazy and cheap isn't the only reason systems DON'T have TXV's. Some systems don't call for TXV's, and a piston is correct.

Please quit making general statements, that aren't correct.

Usually, I run direct vent (2 pipe). Mostly because it cuts down on my clearance to windows. Alot of places still require a combustion air, for the water heater, so the idea of blocking off an existing combustion air is mute.

[acwizard]

Your furnace has been designed by Carrier as a one pipe system. Do not mess with it if you want it to work safely. Where have you gotten the notion that a 2 pipe is better is nonsense. I have been doing installations of furnaces for 34 years now. I always follow the mfg installation requirements. You have been misguided by some of the comments here. Without doing a calculation , the amount of infiltration is minimal in respect to the volume of space in your home and leakage thru windows and doors. Your combustion air is entering the building thru a designed screened opening. Your furnace is more than likely not in a conditioned space, like a closet or basement. If your furnace was rated at 100% efficient , for every 100 cubic feet of gas burned, it would require 1000 cubic feet of air. This is a lot of air and yes there would be infiltration, this is why code requires combustion air openings to the outside when a gas fired piece of equipment is installed. Here is another thought, how much air enters thru the 2" pipe opening. If you are trying to squeeze every nickel of energy out of your furnace and its design , you should consider a different piece of equipment. If you want 100%, an electric furnace would do the trick until you got your first electric bill.There would be no infiltration associated with the electric furnace. Just how do you heat your water in your home, maybe this is more of a problem as far as energy goes. The point I am trying to make is no home is air tight, and 100% energy efficient, think about the health risk if you were locked inside your airtight home. Another thought , commercial building ventilation requirements vary but 5 to 20 or more cubic feet / minute of fresh air is required per person.(see ASHRAE 62.1) My final thought,if this is bothering you to the point where you are losing sleep over it, then invest in a new furnace and install it with the 2 pipes.

[George2]

Some professionals go with a single pipe system, because we can't physically run 2 pipes. I've had a few times where I literally couldn't run a two pipe system, and I had to go non-direct vent. I guess that means I'm not a professional :-\

Also, being lazy and cheap isn't the only reason systems DON'T have TXV's. Some systems don't call for TXV's, and a piston is correct.

Please quit making general statements, that aren't correct.

Usually, I run direct vent (2 pipe). Mostly because it cuts down on my clearance to windows. Alot of places still require a combustion air, for the water heater, so the idea of blocking off an existing combustion air is mute.

I'm sorry that I didn't express myself clearly. Let me rephrase it.

When it's possible for a furnace to be a two piper and when it's possible for an A/C can have a TXV and the installer/contractor doesn't do it..........? fill in the blanks.

I just left a company, that when I joined, neither the owner or the "car" salesman (turned HVAC salesman) knew what a TXV was.

Now I guess that doesn't fall under lazy or cheap.

[Chuckg222]

I only have a one pipe system in my house, I call it my Radon mitigation system:whistle:

[hvacvegas]

I'm sorry that I didn't express myself clearly. Let me rephrase it.

When it's possible for a furnace to be a two piper and when it's possible for an A/C can have a TXV and the installer/contractor doesn't do it..........? fill in the blanks.

I just left a company, that when I joined, neither the owner or the "car" salesman (turned HVAC salesman) knew what a TXV was.

Now I guess that doesn't fall under lazy or cheap.

Much better.

[euroboy]

If it was possible ( which it does not look like is the case ) I would make it a 2 pipe system, since I do believe that is a much better way to install a system, since it does not introduce pressure differences into houses ( and all the associated stack effects recently talked about here ). After all we are talking about Canada here and we have had many days with well over -20Deg C ( -10 F ), and any unwanted air infiltration is not welcomed. In my case the furnace is on way way more compared to the hot water tank, so it is the main source of negative pressure in the house ( in the winter range hood and bathroom fans are used less to allow for humidity to stay in the house ).

What got me going on this project is that I plan to finish the basement - at this point it is one big open space, and the furnace will end up in a storage room - there will be enough volume of air for it and the hot water tank.

Would the majority of currently installed high eff. furnaces be 1 or 2 pipe, and why ?

[acwizard]

If it was possible ( which it does not look like is the case ) I would make it a 2 pipe system, since I do believe that is a much better way to install a system, since it does not introduce pressure differences into houses ( and all the associated stack effects recently talked about here ). After all we are talking about Canada here and we have had many days with well over -20Deg C ( -10 F ), and any unwanted air infiltration is not welcomed. In my case the furnace is on way way more compared to the hot water tank, so it is the main source of negative pressure in the house ( in the winter range hood and bathroom fans are used less to allow for humidity to stay in the house ).

What got me going on this project is that I plan to finish the basement - at this point it is one big open space, and the furnace will end up in a storage room - there will be enough volume of air for it and the hot water tank.

Would the majority of currently installed high eff. furnaces be 1 or 2 pipe, and why ?
I believe all furnace mfgs. give the installer the choice of 1 pipe or 2 pipe installations. Stack effect relates to chimneys and flues. I am really curious ,where is your furnace drawing combustion air from presently. I will agree with you any unwanted infiltration should be minimized.

[George2]

I have sold Bryant/Carrier since they came out with the 90+ % furnaces in 1981.

Actually, they gave us two test models to install in 1980.

I have never seen the above mentioned manufactures have a 1 pipe only furnace.

That really intriques me. Now, a lot of the manufactures I was selling against in the early years had only one pipers and always (of course) used indoor air for the comb. air.

But I can't think of anyone now that doesn't give us the option of a 2 piper (better know as a direct vent to the professionals).

To answer your question about "do most people go with 2 pipes?" YES

[Can-Gas]

Why are you so adamant about having 2 pipes? Are you making you furnace room smaller and feel you won't be providing enough combustion air for the furnace?

Or, like a customer I had not too long ago, do you just want one cause you've seen it on all your friends and families furnaces and you just assume it needs it?

[euroboy]

What I don't like is having a 4" hole in the side of my house that supplies uncontrolled amount of cold air no matter if the air is needed or not :LOL:

Actually it is more of a research project when time comes to purchase a new furnace - as was pointed out in this thread most of the new installs are dual pipe, which I agree is a better way.

My next research project will be to see if there is a 2-pipe hot water tank - I don't like tankless, so I am looking for any other option - recently I was watching the DIY network and they had the following tank:

http://www.hotwater.com/water-heaters/residential/conventional/gas/vertex/power-vent/

Has anybody installed one of those, and what do people think about them ?

P.S. I took a quick look at their manual and it does not look like a 2-pipe system, but it is 96% eff. - impressive :Faint: