Page 22: http://www.xpedio.carrier.com/idc/gr...58mvp-13si.pdf
What's the question?
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.
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?
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.
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.
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.
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.
The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.
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.