Large garage (man cave) hvac

[toohott7718]

Hello I have an attached garage to my house with a ceiling height of 18', it will be insulated with spray foam in the walls (r-20) and at the roof deck (r-30) my plan is to install a 90,000 btu furnace (I already have) in the attic and run my supply lines 6-8 down the wall so the air doesn't have to travel down so far. My question is will my furnace be suitable for this space and what size my ductwork should be. I will be using this furnace basically just for the blower, I planned on buying a heat pump then I would have the bonus of having a/c . The garage is 50x40x18 . I attached a sketch hopefully it makes sense. I am in Wright City, Mo. Thank you for your help!

 

[amg1678]

wish I could build a man cave

 

[gmcgeo]

Hello I have an attached garage to my house with a ceiling height of 18', it will be insulated with spray foam in the walls (r-20) and at the roof deck (r-30) my plan is to install a 90,000 btu furnace (I already have) in the attic and run my supply lines 6-8 down the wall so the air doesn't have to travel down so far. My question is will my furnace be suitable for this space and what size my ductwork should be. I will be using this furnace basically just for the blower, I planned on buying a heat pump then I would have the bonus of having a/c . The garage is 50x40x18 . I attached a sketch hopefully it makes sense. I am in Wright City, Mo. Thank you for your help!

What is the make and model of the furnace, and is it gas? propane? elect?

 

[Rc_Guy]

The chart I find says 100,000 BTU for 2000 ft.² but it is not ceiling height in the consideration. That said I have a 40’X48’X14’ and my little boiler keeps the garage nice and warm all winter in Minnesota

 

[BillK]

Forget about the furnace. What you really need to find out is if a single heat pump will be sufficient for that size space. Then you will have to see if the furnace will accomidate the A-coil to work with the heat pump. With the 18 ft ceilings you will be heating about the same volume as a 4000 sq ft house.

The unit that my business is in is 30 x 60 x 15 and is surrounded on three sides by other units so is fairly well insulated. I have a Modine 170000 BTU hanging gas unit heater for heat and a 5 ton AC unit on the roof.

 

[toohott7718]

What is the make and model of the furnace, and is it gas? propane? elect?

It is a Goodman gas furnace, but I won't be using it as a furnace, basically just for the blower and I'll be using a heat pump. The model number is GKS90904CX hope that will help, I do know it is 1600cfm. Thank you!

 

[gmcgeo]

so using it as the air handler? and you have what outdoor unit?

No problem!

 

[toohott7718]

so using it as the air handler? and you have what outdoor unit?

No problem!

Yes you are correct, I haven't purchased it yet, I wanted to make sure my unit would work.

 

[dcg9381]

I won't be using it as a furnace, basically just for the blower and I'll be using a heat pump. The model number is GKS90904CX hope that will help, I do know it is 1600cfm. Thank you!

If it's anything like the typical Goodman units they do down here, it'll heat just fine until it goes below 35 degrees or so. They forget about it if you don't have aux heat or the furnace setup. You need to find a chart on that thing that has heating BTUs and ambient temperature.

 

[gmcgeo]

I haven't purchased it yet, I wanted to make sure my unit would work.

well for a 1600 cfm fan, "if you are only using as the air handler" then that would be plenty of fan to do the job. the question is, what outdoor unit you will go with to supply to the air handler

 

[toohott7718]

well for a 1600 cfm fan, "if you are only using as the air handler" then that would be plenty of fan to do the job. the question is, what outdoor unit you will go with to supply to the air handler

Yes that's what I'm wondering... spray foam works incredibly well I was just concerned about having high ceilings and how many ton unit to use.

 

[bonneyman]

Sounds like an awesome place! Are you accepting roommates?

 

[toohott7718]

Sounds like an awesome place! Are you accepting roommates?

I've been working on my house for almost 4 years, its a work in progress...

 

[PoorUB]

You need 400 CFM for ton of cooling so a 1600 CFM blower is good for 3.5 -4 tons. I say 3.5 tons because residential furnace air flow falls flat on it's face when you add duct work. That 1600 CFM furnace will be lucky to move 1400 CFM with duct work. It will be marginal for 4 tons.

Tight spray foam? I will bet 3 tons will cool it, but if you plan of heating with a heat pump I would go larger.

If you are going to use the furnace to heat it is over sized. 60K-75K will heat that place.

 

[toohott7718]

You need 400 CFM for ton of cooling so a 1600 CFM blower is good for 3.5 -4 tons. I say 3.5 tons because residential furnace air flow falls flat on it's face when you add duct work. That 1600 CFM furnace will be lucky to move 1400 CFM with duct work. It will be marginal for 4 tons.

Tight spray foam? I will bet 3 tons will cool it, but if you plan of heating with a heat pump I would go larger.

If you are going to use the furnace to heat it is over sized. 60K-75K will heat that place.

Thank you for all the info, I didn't want to run just my garage on gas so that's why I planned on using a heat pump and the extra benefit of having ac. You suggested a 4 ton if I was using a heat pump will that not be too big for ac? I was told years ago when sprayfoam is used that the HVAC equipment is almost cut in half because the spray works so well, do I still need that big of a unit because the tall ceilings? Thank you again for everyones help

 

[PoorUB]

Thank you for all the info, I didn't want to run just my garage on gas so that's why I planned on using a heat pump and the extra benefit of having ac. You suggested a 4 ton if I was using a heat pump will that not be too big for ac? I was told years ago when sprayfoam is used that the HVAC equipment is almost cut in half because the spray works so well, do I still need that big of a unit because the tall ceilings? Thank you again for everyones help

I might go larger with a heat pump as the output drops off as the outdoor temp drops. It depends on the equipment.

Yes a taller side wall will add some capacity.

Also, do you have plans for some sort of auxiliary heat? Are planning to hook up the furnace? A typical HP will not cut it as even in Missouri you can have below zero temps and most HPs capacity will fall off by then.

 

[yeldogt]

Why so many doors?

 

[toohott7718]

Why so many doors?

Its essentially an oversized 3 car garage, but I won't ever have the need for the bigger doors, that is just for resale.

 

[toohott7718]

I might go larger with a heat pump as the output drops off as the outdoor temp drops. It depends on the equipment.

Yes a taller side wall will add some capacity.

Also, do you have plans for some sort of auxiliary heat? Are planning to hook up the furnace? A typical HP will not cut it as even in Missouri you can have below zero temps and most HPs capacity will fall off by then.

I had not planned on using any auxiliary heat because it was a garage, I didn't want to worry about having to run gas (propane) lines and venting, but it definately would be nice to have a back up. Another thought I had was to use my 125,000 BtU kerosene/diesel forced air heater when I planned on being out there. Now you guys are making me think...should I run a gas line just incase? If so what size do you recommend for this furnace? I know normally I've seen 1/2" black iron but if I'm going to run pipe I would rather run one continous pipe.. At one point I was planning on using an outdoor boiler and that was going to be my main source for the whole house ,that still may be an option. Thanks again for everyones help

 

[PoorUB]

Now you guys are making me think...should I run a gas line just incase? If so what size do you recommend for this furnace?

Gas pipe size depends on the pressure and distance.

I put a furnace in my dad's house. They set the meter along side the garage, it was a fairly long run. At 1/2 PSI natural gas I would have had to run 1-1/4" black pipe. I got the utility to run 2 PSI and ran it in 1/2" pipe.

If you are using a gas furnace, hook it up! Why would you want to use portable kerosene heater? Yuck!

 

[Jim greengo]

It is a Goodman gas furnace, but I won't be using it as a furnace, basically just for the blower and I'll be using a heat pump. The model number is GKS90904CX hope that will help, I do know it is 1600cfm. Thank you!

Sounds like a 4t drive according to model number.

 

[toohott7718]

Thanks for all the input, I'm going to run a gas line for auxiliary heat and ill have my furnace changed over to propane, will 1/2" be big enough? I will have 58' of gas line inside then roughly 35' outside to the propane tank. What size trunkline and how many branch lines do you recommend?
Thanks again for everyones help

 

[PoorUB]

Thanks for all the input, I'm going to run a gas line for auxiliary heat and ill have my furnace changed over to propane, will 1/2" be big enough? I will have 58' of gas line inside then roughly 35' outside to the propane tank. What size trunkline and how many branch lines do you recommend?
Thanks again for everyones help

As long as you run 10 PSI gas up to the building, then regulate down to 2 PSI for the run to the furnace, then one more regulator down to 11" at the furnace 1/2" will be fine.

https://www.regoproducts.com/liquid-propane-gas/field-topics/sizing-propane-piping-systems/

 

[toohott7718]

What size trunkline and how many branch lines do you recommend? Thank you for everyones help

 

[dcg9381]

Your furnace should have an indication of what line size is needed. There's a chart above on general line sizes, but it depends on where the propane regulators are at. On my shop, which is regulated down immediately upon entrance (2psi) - everything is 3/4" minimum... But I dunno if that's enough for a 90K BTU furnace. I just set it up so I could branch it additionally later. Course, you pressure test/leak down test everything.

 

[PoorUB]

What size trunkline and how many branch lines do you recommend? Thank you for everyones help

How much duct do you want?

My furnace in may garage has about 5 feet of duct. I came off the furnace with the same size as the outlet of the furnace, and split it in half with two elbows that were half that size.

 

[toohott7718]

I planned on running a trunkline 16' on each side of the furnace and then run my branch lines from it, I'm just nit sure what size the trunk line or branch lines should be, I was thinking 8" for the branch lines but I would like some insite from someone, thank you!!

 

[PoorUB]

1600 CFM divided by 2 is 800 CFM. Each branch will have to start out as a 10x14.

Seriously, you really do not need much duct. We put duct in a house because we want air flow to each room. In a wide open space you can just run a duct out of the furnace and aim to across the shop and it will heat just fine.

 

[toohott7718]

1600 CFM divided by 2 is 800 CFM. Each branch will have to start out as a 10x14.

Seriously, you really do not need much duct. We put duct in a house because we want air flow to each room. In a wide open space you can just run a dust out of the furnace and aim to across the shop and it will heat just fine.

My dad has an ahu in his garage with a 3' plenum and a vent and right off it and it heats his garage well, I'm just trying to make the garage as comfortable as possible. Thank you!!

 

[PoorUB]

My dad has an ahu in his garage with a 3' plenum and a vent and right off it and it heats his garage well, I'm just trying to make the garage as comfortable as possible. Thank you!!

I used to do HVAC. My own garage has a horizontal furnace mounted up against the ceiling. I have AC so a cased A coil then about three feet of duct that turns into two elbows about 10x7 each that are aimed across the shop. Return is just a short transition to a 20x25x4 filter box.

It will feel chilly against the over head door, I should of turned the furnace around and blew it against the door, but it is only a few feet from that end of the garage and I would rather have it blow the other way, into my work area.

I have one ceiling fan and that helps stir up the air.