High Efficiency Furnace intake pipe does not go outside. Is that OK?

A lot colder than you and 25000 would be perfect. I have a 35/50k input 80%+ unit strapped down to 3500 (about 29000BTU out) Monday was the coldest day we have had in 200 years and the furnace ran less than 9 hours. (-36C, and windy)

Remarkable ! Impressively low consumption and boy you sure get LOW temperatures !

A lot of homes, older ones, are also over sized. When I did HVAC install, we almost always put in smaller than what we took out. One man did insist on a larger one, boss did his best to reason with him, but it wasn't working.

As for myself, I took out a 80k and put in 70k, this being in 1994. Still over sized.

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My brother's trailer has a bigger furnace than my house and a whole lot less insulation.

furnace makers moved to outside air because it can be cleaner, inside air can have things like chlorine bleach in it, that led to early corrosion and heat exchanger failures.

tis from a HVAC buddy of mine who taught it for 25 years.

That doesn't sound so great. I have a 3100 sq ft house, my heating, cooling, hot water total is at least $500 a year less.

Backdrafting.

I guess it's possible. Can't see what the study actually consisted of without having paid access. The question would be what kind of appliances did these highly sealed houses have? You would think it would have a high efficiency direct vent furnace for example. That would eliminate the furnace as a possible force. What's left? WH? Again typical energy efficient new house likely has a power vent WH. It would be interesting to see the study to find out how the CO they measured originated if they are using modern appliances. With an old furnace using a traditional chimney, old non-power vent water heater, etc then I can see it being a problem, but those appliances in a new house seem unlikely.

Not really claiming especially low bills here, but in my local climate which is in upstate NY this is a rather typical situation.

replying to bob haller, Old guy wrote: I

Sigh. This is an old thread, it's all been discussed before. It's generally permissible to install a furnace using indoor air for combustion, no outside air intake. Install manuals typically show both that way and with an outside air intake.

Furnaces and boilers used inside air since they were invented. Using and outside source for combustion air is just in the past couple of decades. The only difference is efficiency. Anything going out the stack has to be replaced by sucking cold outside air in through every crack in the house.

erally permissible to install a furnace using indoor air for combustion, no outside air intake. Install manuals typically show both that way and with an outside air intake.

Depends too on where the furnace is. If it's in heated living space, it's worse. If it's in an unheated garage or basement, then it may not make much difference. For one thing, if you bring in 20f outside air, the furnace w inds up heating it too, ie you get less heat output than if it used 50f bas ement air.

enerally permissible to install a furnace using indoor air for combustion, no outside air intake. Install manuals typically show both that way and wit h an outside air intake.

t's worse. If it's in an unheated garage or basement, then it may not make much difference. For one thing, if you bring in 20f outside air, the furna ce winds up heating it too, ie you get less heat output than if it used 50f basement air.

The furnace doesn't have to preheat the combustion air. If you put 20F air into it versus 50F air you'll get less heat out, because the incoming air is colder and some of the combustion heat goes into raising it's temperature.

And as far as that

That you're not heating the basement air much via the furnace was part of my point. The leaking air coming into the basement from outside gets heated from 20F to 50F partly by the earth surrounding the basement. But some heat is coming from upstairs, etc, it gets complicated.