58MVP Combustion Air from outside or inside?

[jeffs]

Quick question about the Carrier 58MVP combustion air setup. The furnace it replaced (4 year old Carrier builder's model) did not use outside air for combustion, so the installer did not change this for the 58MVP. His thought was to follow the lead of the last installer.

This can be easily remedied if necessary but I'm not sure if it is. The Carrier documentation calls for outside air.

Any thoughts?

Thanks for the help!

[jetstream]

It's necessary! Must be direct vented. Must follow installation instructions, no question.

[docholiday]

Why anyone would defeat the efficiency of a 90+ by single pipe is beyond me. (pulling in outside air through cracks costs money). There is also the chance you starve the furnace of combustion air.

[wayner211]

It can be done and it does not lower the efficiency. I know this for a fact and I'm sorry but I can't tell you where I work.

[RoBoTeq]

I agree with doc. If it were up to me, all condensing furnaces would be required to utilize outside combustion air.

It may not reduce the efficiency rating of the furnace but it certainly does reduce the efficiency of the completed system when conditioned air is blown out the venting and unconditioned air to replace the wasted air is brought back in through leaks in the house.

[smadave]

You must take the combustion air from outside with this furnace!!


Dave in NJ

[masterair]

It does not have to be brought from outside if the furnace is in a crawl space, unfinished basement or attic. But if the instructions say do it then standard practice should be do it.

[jeffs]

Thanks everyone for taking the time to respond.

It sounds like combustion air from the outside is the way to go. The furnace is working the way it is but I've always wondered.

The installer mentioned that changing the setup might negatively affect the existing air pressure setup in the house. I have no idea how to measure that, guess I should have checked here!


Thanks again!

[york_hvac]

Ive read the manual, 58MVP is NOT approved for 1-pipe vent system! However, Carriers new model, 58MVB, is approved for 2-pipe or 1-pipe.

[ryan_the_furnace_guy]

Originally posted by smadave
You must take the combustion air from outside with this furnace!!


Dave in NJ

Please don't quote me on any of the following...

I half-heard it from the installers I work with, we do Carrier. Supposedly the new generation of high-efficiency/condensing furnaces can use a "one" or "two" pipe setup. (and I don't mean concentric) I mean they can breathe and burn inside air. Don't shoot ya'll, this is just what I heard.

Either way, if you value the life of your equipment, I would absolutely demand it use outside air for combustion.

[ryan_the_furnace_guy]

Originally posted by york_hvac
Ive read the manual, 58MVP is NOT approved for 1-pipe vent system! However, Carriers new model, 58MVB, is approved for 2-pipe or 1-pipe.

Yup, what ^he^ said. :)

[heatpumpguru]

I was at the class and 58MVB will be able to be 1 pipe and will see the CARRIER guys in Las Vegas,and we thought TRANE outdoors were BIG!!!

[jeffs]

Okay, now I'm confused!

Carrier 58MVP080-F, inside or outside air for combustion? Carrier manuals say outside, some installers are saying inside, others outside.

The installer of this system is a super guy, I don't want to call him back and sound like an idiot, or perhaps more than usual...

Thanks, I do appreciate the help.

[jrbenny]

Page 22: http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/58mvp-13si.pdf


Step 9—Direct Venting
The 58MVP furnaces require a dedicated (one 58MVP furnace
only) direct-vent system. In a direct-vent system, all air for
combustion is taken directly from outdoor atmosphere, and all flue
gases are discharged to outdoor atmosphere.

What's the question? :rolleyes:

[docholiday]

Originally posted by wayner211
It can be done and it does not lower the efficiency. I know this for a fact and I'm sorry but I can't tell you where I work.

So who pays for the air coming in through the envelope of the house that will only be heated then be used for combustion and sent back outside?

When I say efficiency, I mean efficiency. AFUE would not be affected but the cost of heating the home would be greater with a single pipe system (unless its in an attic or crawl space).

Now there is an instruction manual. It either says direct vent only or it allows for 2 pipes. My understanding is two pipe (direct vent) is the only acceptable practice on this furnace.

[novakht]

It is a better system 2 pipe...... we can argue all day if it reduces the actual furnace efficeny by using a single pipe install--but by bringing in the outside air via sealed combustion makes the sytem more efficent.

[Carnak]

The manual will show approved venting methods for the furnace. If this is a condensing furnace and it only approves direct air from the outside ducted directly to the unit, then it shall be installed that way.

From an energy standpoint, you make better use of your fuel with the combustion air ducted directly to the furnace from the outside.

[jeffs]

Thanks everyone for your input. It is appreciated. I don't know of anywhere else where we can find this much HVAC knowledge given so generously. Hopefully I will be able to repay somehow, someday.

The decision on installing this furnace using combustion air from inside the house was based almost entirely on the fact that the furnace being replaced was set up that way. I believe too many variables were not considered, or at least if they were, they were not communicated to me.

I will ask the installer to change the combustion air setup to outside air.



Thanks!