Garage heater advice

[Revolver]

Maine.

I'm looking to maintain heat in my small garage all winter because I don't like to go "fire up" the heater in a frozen garage, wait for it to warm up, then still have frozen tools, toes, etc. I currently have a real need to utilize my shop more in the winter and my tools are slowly deteriorating from condensation. I've done quite a bit of research and would like some input.

Garage specs:
14'x24' 10' ceiling
Concrete slab
2x4 walls
Fiberglass insulated.
9x8 insulated garage door (this is my weak link, I will be installing weatherstripping and additional insulation to the door)
I am in the process of adding 3" rigid foam insulation to the exterior and in the attic. Making it very tight.

I would like to go propane. I like it, seems to require less maintenance (correct me if wrong). I currently use a small wall mount propane heater, I own a few 100lb tanks that are all set up, lines, etc.

First I was looking at the Mr. Heater Big Maxx units which are reasonably priced but I got reading that having separate combustion heating is more desireable? So now I am looking at the Sterling GG45, which with the concentric vent kit is twice my initial budget. But it gets great reviews and I think it would be worth the investment.

Questions...

1. I know a heater that is too small will not be effecient. What about a heater that is too big? I'm thinking the 30k btu might be pushing it so I decided the 45k would be a better choice?

2. Am I to understand that by drawing combusion air from outside that this heater will not need to draw cold "make up" air into my heated area? increasing effeciency over the Big Maxx and similar heaters?

3. What temperature should I maintain in the winter to avoid excessive condensation, then when I am in the shop I can turn it up.

Any input is appreciated.
Thanks.

[rondog]

Man, I'd have to say to consult a local HVAC pro. Someone that knows your local climate and can do a visit/survey and give you a realistic idea and quote.

[Hickory]

Some insurance companies will drop you if they fine out that you have a heating system with an open flame in a building where gasoline vehicles are parked/stored.

[dkf]

Expect to go through at minimum 2 - 100lb LP tanks a month to heat that space depending outside temp and what inside temp you want to maintain. Just maintaining 60 degrees in a single car garage with some heat coming from my basement (6" duct with blower) from my coal stove. I use a 100lber in under a month. This is with a wall mount blue flame. Don't usually get as cold here in PA as Maine.

I bought a small pot belly stove (will burn coal) I am going to put in to help supplement and forget about the LP.

[turmech]

Revolver,

Based off your specs you listed I did a load calculation. I came up with a heating loss of 20,282 BTUs. The cooling gain was 9,507 BTUs

This may be flawed in a few areas:

The program I use does not have anything I can put in for a garage door, as it was designed for residential. Just a EWAG I would figure the door depending on construction would be an additional 5,000 to 15,000 BTUs.

You did not mention the R values of the insulation or any information on windows. I used R-13 walls and R-19 ceiling. I entered 40 ft2 of glass on the SW & SE sides and 40 ft2 of glass on the NW & NE sides.

The design temperatures vary through Maine by my manual J. I used a winter design temperature of -14 outside (lit was listed at between -1 and -14 depending on location) and 70 inside.

The estimated annual heating cost was $850.77 and would be effected by the above factors as well. I used $3.25 for the cost of propane, 85% AFUE for the furnaces efficiency, and 70 degrees for the inside temp (cost would be reduced at a lower temp).

As far as efficiency a vent free heater will always win over a vented. A vented heater will lose heat up the vent pipe and vent free would have no choice but to put 100% in the space. That being said I would not use a vent free heating in an unoccupied space or a bedroom for safety.

The 30,000 heater would appear to be enough based on the load calculation. If the building was around here that would be the size I would use. In your case however I would recommend the 45,000 BTU heater based off the unknown of the garage door.

[LynC2]

1. I know a heater that is too small will not be effecient. What about a heater that is too big? I'm thinking the 30k btu might be pushing it so I decided the 45k would be a better choice?

I would go with the larger size considering it is a garage and less likely to be as well sealed and insulated as a home.

2. Am I to understand that by drawing combusion air from outside that this heater will not need to draw cold "make up" air into my heated area? increasing effeciency over the Big Maxx and similar heaters?

You are correct about pulling outside combustion air and it will be a sealed firebox that one doesn't have to worry about gasoline vapors being ignited from inside if a spill were to occur. The other advantage is there wouldn't be any condensation of water vapors from the byproducts of combustion. An unvented heater will cause everything in the garage to "sweat".

[HeavyMetal]

buy a small pellet stove and set it up to run all winter.

I have familiy in Reno and this is the local hot tip for heating on the cheap in the winter, I've seen auto feed systems as well so the thing doesn't get touched all winter.

Check them out you might save a buck or two over propane.

[Bad Water Bill]

Check with a furnace supplier. I have known many mechanics that volunteered to take the used but working furnace away for free.

Customer saved a few bucks,dealer saved a trip to the scrap yard and you got a furnace that heated a whole house at a given temperature all winter just for the pick up.

One such deal heated a large 2 car garage AND a working green house near Chiraq.

[Lloyd Smale]

one thing to keep in mind with non vented propane stoves is they add moisture to the air not take it out. My reloading room is heated with one all winter and its a constant losing battle to keep steal from rusting in it. If humidity is consern think seriously on a vented stove.

[Freightman]

Move to Amarillo humidity in the winter runs about 15%

[Marvin S]

The over head or (unit heater) is very hard to beat and is made for shop use. I use a 150k btu in a 24x40 shop and its just right. Loyd is right on about the non vented making moisture, I have one from Northern Tool as a backup in the house it works great but fogs the windows after several hours.

[shooter93]

If propane is available to you you may want to BUY a tank. My shop/garage is 24x28 with an 18 foot wide insulated garage door.. I use a propane wall heater of 25,000 btu's and can cook you out of there quickly. In 25 years I have replaced one 15 buck thermostat and one 25 buck squirrel cage fan. I keep it around 45-50 unless I'm working in there or spraying finishes. You buy your tank so you can shop for propane...it will vary as much as a buck a gallon around here.

[rondog]

My dream is to have a heavily insulated shop with a hot water radiant system in the floor. I knew a guy that had that, and you could walk barefoot in his garage in the dead of winter. And where a forced-air heater heats the air in the shop, the radiant heats everything in there to the same temp and keeps it there. I really want it. Not a garage so much, more of a big workshop that rarely sees the door opened.

Ah, pipe dreams.....

[unclogum bill]

I took an oversized used gas house unit and hung it from the rafters. The thermostat came from Graingers and you could regulate it down to 35 degrees Heated Garage to 40 degrees normally. When I needed more I turned it up. Being oversized it heated up quick. Did plumbing, so truck was always easy to start. No frozen drain cleaning stuff. 40 degrees was about right and beat the heck out of walking into one at minis thirty. One man can hang a furnace by himself using 4 eight foot lengths of 3/8" rod and Some 2" by 1/2 flat stock as top and bottom cross pieces Drill some holes in flat stock and run rod through them. Thread nuts on. place a vice grip on each nut and start twisting. It will be up quicker that you think. Them cut rod when its in place that you can the nuts up. use it again for some other project. Most code requires a shut off 2 ft from unit. Silly I think if its in the air. I would add a extra, lower one as well. Maybe where it leaves the garage.

[Revolver]

Thanks for your feedback everyone and for the calculations, it would be great if you could plug in the R-values below and 50 degrees.

I figure an r-value of 33 on the walls and 40 on the ceiling once I have the 3" poly-iso on the outside. I am trying to make it as tight as I can and will be using caulking and expanding foam to fill any cracks as I install the foam sheets. I may only need to open the garage door a handful of times over the season to swap vehicles I am thinking about making some poly-iso "plugs" for the outside of the garage door opening.

My goal is to super insulate it and use an efficient heater which is why I was looking at the 83% effecient sterling with the concentric vent kit for external combustion air. I was not and am not considering ventless.

I was also wondering if I should dig down next to the sides of my slab and bury a rigid foam frost barrier to help slow energy loss into the ground.

Thank you.

[Jeff Michel]

I put a vented wall mounted furnace in my shop about 25 years ago, lasted about 15. I don't remember exactly what I paid for it but it wasn't cheap. It wasn't very efficient as furnaces go either. It's replacement is a non-vented, wall mounted propane furnace. My shop is about the same size as yours, including a large sliding door that isn't insulated. I keep the temperature at 60F all winter long and a five hundred gallon tank lasts a bit more than two years. As Lloyd pointed out, a non-vented heated produces and enormous amount of moisture, something like a quart for every gallon burned. The alternative, at least for me was a small dehumidifier. I never have had any rusting problem on lathes, mill, hand tools, firearms, you name it. I have more problems with rust in the house.

[turmech]

Revolver,

When I change the R values to R-30 in the walls and R-38 in the ceiling (the program only has standard R values with no option for R-40). And the inside design temp to 50 I get the heating loss is 13,841 BTU. The estimated heating cost is $556.17 (the lowest inside temp allows to be used for this is 68). These calculations again would not allow for the garage door.

These load calculations are good and what I use for sizing homes, but I never let them replace my judgment gained by 20 years experience in the trade. That said I would not go lower than a heating system with 30,000 BTU output (not input). And unless you are confident with the R values and air tightness of the door I would possible go to the 45,000 BTU. Really had to say without seeing the structure.

[gbrown]

My question is what type of use is the garage? A true garage to park a vehicle in or is it more of a shop? I have a garage, but we don't park the cars in it. Other than some spray paint and aeresol lubricants, there are not combustibles in there. If you park the vehicles in there, there are some issues, as Hickory posted. I live in a milder climate, but within 10 blocks of me, there are houses which burnt down, either partially or completely, because of vehicles and open flames.

[turmech]

Just to add to my last post: It is not that I don't trust the load calculation. I just know it cold up there, and not being able to see the building to get an impression of what you have, I would not want to see you buy a heater too small.

[Bad Water Bill]

Before starting with the outside insulation why not wrap the garage with Tyvek and seal off a thousand small places where cold air can blow in?