Is this normal run time for a garage furnace?

[Darren889]

So I have a *edit (24x29) attached 3 car garage (11 foot celing), 1 shared wall with the house. It is a new construction house with r8 garage doors, I did the attic with r30 batts and drilled and filled the walls with celulous. I have a nest thermostat installed and set at 50 degrees Fahrenheit, the furnace is a big maxx 50,000 BTU. I live in Minnesota and we have been getting some colder days getting below 0. On those days I have been getting run times at around 6 hours a day, when it is around 20-30 it runs for 10-15 min an hour regularly. The 2 car door opens 2-4 times a day for cars to come in and out of. Is this about normal run time? I was hoping for less, maybe I need to get up in the attic and double check the insulation. I am also thinking about adding R11 to the attic in parallel.

 

[Bert_]

On very cold days I would expect it to run most of the time. Otherwise it's oversized.

 

[Showkey]

25% ( 15 minutes per hour) of the time with good insulation sounds reasonable especially with door openings.

625 sqft could have been done with 30k unit especially when it’s attached to the house.

 

[exactly]

25% ( 15 minutes per hour) of the time with good insulation sounds reasonable especially with door openings.

625 sqft could have been done with 30k unit especially when it’s attached to the house.

Is this to say I should absolutely go with 30k vs 45k for my two-car, insulated, attached garage, also in Minnesota? At some point I will get around to this...and I was leaning towards 45k input BTU on a separated combustion unit by Modine, Reznor, or Sterling. A local contractor suggested the Modine high efficiency unit for the convenience of PVC intake and exhaust, but the smallest one is 50k input BTU and almost as much output BTU, making its heat output substantially higher than even a traditional 45k unit.

 

[bored350]

25x25 typically doesn't add up to a 3 car garage unless you pull all 3 in and can't open the doors?

Regardless, I suspect your ceiling is losing quite a bit of heat and the tall wall height is also adding a substantial volume to the room. How high up is the furnace mounted and where is it pointed?

Check the doors for leaks (a poor install can negate any R value) as.well as the attic insulation. I would blow in 6" or more of cellulose over the ceiling batts and wouldn't even consider rolling any more batts.

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[BillK]

The 2 car door opens 2-4 times a day for cars to come in and out of.

This is what is killing you, not the lack of insulation.

 

[Darren889]

25x25 typically doesn't add up to a 3 car garage unless you pull all 3 in and can't open the doors?

Regardless, I suspect your ceiling is losing quite a bit of heat and the tall wall height is also adding a substantial volume to the room. How high up is the furnace mounted and where is it pointed?

Check the doors for leaks (a poor install can negate any R value) as.well as the attic insulation. I would blow in 6" or more of cellulose over the ceiling batts and wouldn't even consider rolling any more batts.

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Sorry 24x29 is the measurement, a little off. Thanks for the recommendation on blowing in some more, I may blow in fiberglass just to keep it all the same.

 

[Darren889]

Yeah, I am probably going to get an opener on the 1 car door and use that stall for the car that gets pulled in and out more.

 

[BillK]

Yeah, I am probably going to get an opener on the 1 car door and use that stall for the car that gets pulled in and out more.

Try leaving the doors shut for a complete day and see what happens ? Every time you open that door even for a minute the poor heater basically has to start from scratch.

Also, if you are pulling in cars from outside they are giant blocks of ice even with the engine heat. So the heater has to heat them up along with the rest of the garage.

 

[finn]

BillK is correct. A two ton car chilled to 0 F is a huge heat sinl. That’s a lot of BYU’s to warm up 50 degrees..

To mr. Exactly, I wouldn’t put a high efficiency condensing heater in a garage. You will be stuck with heating the garage every day, no matter what changes in your life, to keep the condensate from freezing.

Then there’s the condensate drain issue. It can’t just go out the wall or the discharge will freeze up.

 

[toyotadriver]

Sounds good to me. Be a good idea to increase the ceiling insulation. As mentioned, moving cars in and out requires a lot of makeup heat.

 

[NUTTSGT]

If you're maintaining the heat full time, opening the door for a few minutes isn't the problem. The heat soaked into the concrete will easily overcome that.


The issue is the cold vehicles that are coming into the garage.

I'd suggest to try adding a box fan in front of the vehicle running on low. This will help circulate the warm in and around the garage. It'll also pus the warm engine heat out from under the hood to warm the car back up.

Try a few easy things first, like the box fan or bump the t-stat up to 52°. make sure to keep a tab on the outside temp as to compare variations.

Nothing wrong with adding a blanket layer of unfaced R-11/13 perpendicular in the attic. It won't cost much to do that. Probably get a ROI in the first heating season with it.

 

[Denwood]

If the vehicle had a warm engine and cabin coming in, it may actually be adding a few BTUs. This is based on my observations bringing a warm vehicle into an unheated (but insulated) garage..the hot engine block, coolant, exhaust etc all adds heat.

The three doors are your largest heat loss, but adding insulation to an attic in our climate is not wasted dollars. Make sure each door is sealing properly as even a small opening = a lot of BTUs out the door. Focus your attention on the doors first.

That said, your ceiling is 11' and that is a large area. Your runtimes on a 50K BTU furnace don't sound unusual.

 

[Mainiac Mat]

Could be your thermostat location. If in the line of fire of the heater it may be shutting the unit off before the room is up to temp.

Back wall behind heater is recommended, that way it measures the heat of the return air.

Also, I think that if you run a detailed heat loss, you may find that 50K BTU is marginal for your shop.