I Need a Heater in My Shop!

[sick467]

I have been using wood heat for the last many years and it's time to out-grow cutting firewood!

I think I want a propane heater as my house uses propane and that would be convenient.

I hoping to learn enough that I can size the unit correctly and install it myself (with a little help from my friends). I'll start by asking how to size the heater with the following information...

Facts:

My shop building is 50x50 with 12 foot ceilings, 2x6 insulated (R19) walls, R30 in the ceiling, and concrete floor. My workspace is a 30x30 corner room in this building with an insulated 18' wide garage door and is where I spend most all of my time (same insulation values as the building).

Goals:

I want to be able to turn the heat on in the work room and be taking my jacket of in 10-20 minutes (starting at 40-50° and getting to 60-65° in a short period of time). My oversized wood stove has spoiled me, I guess.

I want to easily get the temp up to 75° and maintain that in the workspace. I rather enjoy working in a T shirt in the winter hence the summer time temps that I am after.

On occasion I will want heat in the remainder of the building and I currently put a fan in the workspace door and circulate the heat out to that area. It is not important to get that area overly warm, just not cold (55-60°). This is easy to do with the wood stove as it can get the work room up to 90° with a few more sticks of firewood. At times, the work area gets too hot and I use the doors leading to the remainder of the building to cool off the room.

Concerns:

The web guides I have found warn about oversizing the unit, but it sounds like that's what I want. I am used to the wood stove and the shop seldom goes more that a day or two without me heating it up.

I am also concerned about the noise. I want it as quite as possible.

Questions:

Would it be more efficient to size the unit for the room and just keep it set at 60°, turning up for the weekend to 72°? OR would it be better to oversize it some and treat it like the wood stove...turning it on when I'm there and off otherwise? I spend a couple hours there in the evenings and most all of the weekend.

Bottom line (after all that wind I produced)...where to start with respect to sizing the unit?

All ideas and advise are welcome!

 

[Jackfre]

I would use a Rinnai EX-38. It is likey to be a bit undersized, but I would run it for a year or so and see how it does. In my 1000 sq ft shop I can sit right next to mine and it's operation is not objectionable. Costly, but you get what you pay for. Vent pipe is included and requires only a 2.5" hole. Programmable stat is built in. Modulating burner and fan.
It will do a great job in the shop. The idea of oversizing to handle the storage area for occasional use makes the primary area always oversized. You will be best after the trial year or two to get a second heat source for the storage area.

 

[C2F]

https://www.loadcalc.net/

Use this site. It will help you with your calculations. Let me know what it comes up with.

 

[spudley]

Never heard a Rinnai but the 75K Hot Dawg I have sounds like a jet taking off. Great heat but too noisy for my liking.

Oh well, it was free.

 

[sick467]

Great calculator C2F! It really takes alot into consideration. I have more faith in that than the ones that have 4 inputs and all come up way different. I think I entered all the required values correctly and came up with a BTU rating for the 30x30 workspace and the "L" shaped storage area separately...

30x30 Workspace (alone) = 38015 BTU

"L" Space (alone) = 64433 BTU

Jack - according to the calculator CF2F posted, you are real close with your recommendation. However, the Rinnai unit is mounted at the floor up against the wall and I have no room for that. The heater I end up with will have to be ceiling mounted.

Spudley, Thanks for the warning on the 75K HD unit! Hopefully I don't have to oversize that far. I think, in order to keep the work area as quiet as possible, I will have to size for just that area and consider a second unit for the "L" Space should it be desired (like Jack said).

I really appreciate everyone's help. It can be so contradicting from site to site.

How does the calculated BTU rating of 38K BTU/hr sound for my 30x30 workspace compared to others with similar areas to heat?

 

[Jackfre]

I’ve had these Rinnai’s in my homes, basements, garages and shop since ‘91. I wouldn’t be without them in my home. Of course the commissions I made selling over 250,000 of them helps me feel that way I like to install them under windows as windows are usually difficult to decorate under and that space opens into the living space for good air circulation. I have the EX-38 in my shop in the center of a wall and under a window. At 26.5” tall on a 5” wooden base I’m coming in at 31.5” tall. My current plan is to build a bench along that wall over the heater. I will make a hinged panel to access the controls and filters. As long as I don’t build up **** along the sides obstructing air circulation I will be good. I built the 5” base to protect the unit from my rolling equipment. It is not necessary if under a table/bench. Show me a floor plan. I don’t own a Db meter, but will post a video later so you can not hear it.

 

[sick467]

I have no room for a floor model.

 

[TractorJeff]

How does the calculated BTU rating of 38K BTU/hr sound for my 30x30 workspace compared to others with similar areas to heat?

I am 30 by 32 using a 50k Big Maxx

 

[Showkey]

Bottom line, ball park estimates will get you close enough as there only certain number of choices 30-50-75-100-125k heaters.

So the charts seem to work with slight adjustment for climate and insulation:

 

[sick467]

Thanks for the reference Jeff...50K seems like the right size for the workspace.

Showkey, I have to say that your charts agree with this conclusion. I tried several quick and easy online "calculators" and they ranged from 21 up past 100K BTU. Not so conclusive. Thanks for joining my quest and adding to my confidence level.

It looks like we have converged on a 50K unit, which is nicely oversized as I was leaning towards oversizing anyway. This would add some decent heat to the "L' space on the rare occasion, I think.

Now, Options...I like the idea of pulling fresh combustion air in along with venting the exhaust out (exhaust out is a given) and I read that condensation can be a problem with either. Without venting, condensation/high humidity in the shop, and with venting...potential condensation in the intake duct work. I have no available drain near the corner where I want to hang this unit. Am I understanding it correctly that the fresh air intake systems need a drain for condensate?

 

[Showkey]

Outside air intake to the heater will not raise the humidity levels in the heated space.
Heating the space will lower the humidity of the space. Bringing cold wet and snowy vehicles into the heated space will substantially increase the humidity indoor levels.
If no vehicles are are coming or going humidity levels should be very low.

Example of that low humidity:


Outside air intake might cause more condensation internally in the heater itself and may cause more water/condensing in the exhaust.

Warm exhaust hitting the cold outside air will create water vapor condensation and water dripping from the exhaust pipe.

 

[sick467]

So, the units with the outside intake air don't need a condensate drain?

 

[Showkey]

So, the units with the outside intake air don't need a condensate drain?

It depends, distance, tilt of the pipes, temperatures and temperature difference.........most of the instructions manual say or mention drains on commercial units.

These garage heaters are not condensing heater units like the 90 plus units in home. True, Condensing units are vented using PVC as the exhaust temp are lower.