Furnace in attic of garage - condensate Q

[rcevan]

I talked with my heating contractor yesterday regarding a garage I'm designing. He says that a high efficiency furnace placed in the attic would need a sump pit and pump so the condensate will discharge quickly and won't freeze in the winter (Minnesota).

Are there any other options? I didn't ask him how small a sump could be installed.

He proposes a lower efficiency furnace (85% I think) so there's no condensate to worry about. If the high efficiency is not too much more, I'd put it in and save the natural gas for my grandchildren. :angel:

P.S. I'm doing a/c also, thus the furnace. I'm installing a basement workshop.

[hvacvegas]

I talked with my heating contractor yesterday regarding a garage I'm designing. He says that a high efficiency furnace placed in the attic would need a sump pit and pump so the condensate will discharge quickly and won't freeze in the winter (Minnesota).

Are there any other options? I didn't ask him how small a sump could be installed.

He proposes a lower efficiency furnace (85% I think) so there's no condensate to worry about. If the high efficiency is not too much more, I'd put it in and save the natural gas for my grandchildren. :angel:

P.S. I'm doing a/c also, thus the furnace. I'm installing a basement workshop.

I wouldn't suggest putting a 90%'er in an open attic, in the north.

Let him put the furnace in, and then build a room around it, insulate the crap out of it. Then it's not in an open attic. Less likely to freeze.

Also to note, if the DOE has it's way, and you want the 80%'er up there, you better jump on the ball. The clock is ticking for you to be able to even buy low efficiency furnaces in your area. I don't remember the date though.

[skippedover]

FYI, in May of 2013, you'll have no choice but to install a 90+% gas furnace in Minnesota, due to DOE energy requirements. That said, we've been installing 90+ in attics here in New England for years with no issues. It may be necessary to build a small room around the furnace an remove any insulation in the floor below it, such that the furnace is now in a 'conditioned space'. There are methods of dealing with the condensate such that is doesn't freeze and in fact, once the new codes kick in in just over a year, all of these issues will need to be addressed. In Minnesota you should take advantage of the longer, colder winter months and enjoy the higher efficiency.

[motoguy128]

you coudl also look at doing it as an unvented attic, insulate under the roof deck, then don't insulate the attic floor and it will be semi conditioned. You will need ot factor in that small amount of additional space that needs ot be heated. But for a attic furnace, I'm guessing it will be a little oversized anyway to warm it up quickly after the door has been opened.

Having a warm garage in winter is wonderful. My garage is a walk-out portion of my basement. Totally worth the added expense to heat it IMO. Mine is only passively heated by still stays above 50F all winter.

Keep in mind with a heated garage, that most furnaces shouldn't be operated ot maintain a temperature under 50-55F. You can cause the flue gases to condense in the primary heat exchanger... which isn't intended to handle condensation. You might even want a relay interlock with a switch on the garage door so the furnace won't run if the door is accidentally left open.

Finally, if you intend to occupy the garage, consider installing a ventilation fan that runs 24/7 to keep the space slightly negative and ventilated so you don't have a build-up of toxic fumes. I have this on my garage since it's attached to the house is such a way that it's not sealed compeltely air tight. It makes a huge difference.

[rcevan]

Thanks for the responses. Especially about the relay for the "door left open" lockout.

1) its a detached garage
2) it will be well insulated and the attic space will be conditioned space

Therefore, the condensate freezing as it drains outside is the problem.
If the room-in-attic trusses are 2x12s (or 2x10s) I didn't ask the contractor if there are sumps that are shallow enough to fit in that space so the base does not extend down into the main garage ceiling.

That's why I was looking for any other option you'd know of that I could offer the contractor.

I trust this contractor as an individual, I've known of him for 2 decades and have hired him several times. So, I'm willing to not "shop around" as long as he stays reasonable.

AGAIN, If its not worth the extra $ to put in the 90+ %, I can just do the 85? %.

Thanks

[motoguy128]

You don't have a drain already in your garage? Can you tie to plumbing in the house?

IF you don;t ahve a drain within reasonable reach, then I would just look at an 80% furnace or a direct vent unit heater or radiant tube heater.

I'm still confused about the sump. The unit is up high, you should be able to use gravity to drain it within the conditioned space.

[rcevan]

You don't have a drain already in your garage? Can you tie to plumbing in the house?

IF you don;t ahve a drain within reasonable reach, then I would just look at an 80% furnace or a direct vent unit heater or radiant tube heater.

I'm still confused about the sump. The unit is up high, you should be able to use gravity to drain it within the conditioned space.

The main floor will be prestressed concrete. I haven't talked with the two concrete contractors about a drain for the floor and the options there.

If the condensate drain slopes to outdoors it will freeze up. The contractor said that the pipe needs a good volume of flow at a time to prevent the freezing.

Your question leads me to wonder if the condensate drain could go down and be tied int the drain for the main garage floor. I'd still have to worry about freezing but that drain may need a similar design concern of freezing.