On Demand Heating Option

[bedn0009]

All,

I'm building a 32 x 28 garage with a second story in Wisconsin (it's cold in the winter). I'd like to know the best option for a furnace that I can keep at 40 degrees all winter, turning up when needed, but also one that I can shut down completely if I choose (not parking in there consistently). This will be used for woodworking and storage... the upper level not finished yet, but would imagine that space will eventually be some type of living space.

I've decided against in-floor radiant... initial cost is too high, and I don't want to be locked into keeping it on all winter. I will run natural gas to hte building (along with electrical) and my ceiling height is 9 feet.

Am I limited to hanging unit heaters? Why doesn't anyone use traditional furnaces like we've go in our homes and duct them?

 

[pseudorealityx]

People don't typically use ducted traditional furnaces because it costs more, takes up more space, and being a garage, air distribution typically isn't a high priority.

There is nothing stopping you from going that route.

Given that you are potentially doing a living space above... you cannot (and shouldn't) share the same HVAC system between the garage/workshop and the living space.

 

[bedn0009]

People don't typically use ducted traditional furnaces because it costs more, takes up more space, and being a garage, air distribution typically isn't a high priority.

There is nothing stopping you from going that route.

Given that you are potentially doingk a living space above... you cannot (and shouldn't) share the same HVAC system between the garage/workshop and the living space.

Thanks. So what options does this leave me with?

 

[Kevin54]

I have a Hamilton 45,000btu hanging heater, and I keep my garage at 50 during the winter and crank it up when I am out here. As long as you have an insulated garage, you should be good. With mine, you can run off of natural gas or propane by switching the jets. I run mine off of a 120 gallon propane tank and it will last a month to a month and a half as I am out here quite a bit.

 

[Jackfre]

Rinnai EX38. Built in programmable stat that can be sets to 40 and will restart after a power failure.

 

[bedn0009]

Rinnai EX38. Built in programmable stat that can be sets to 40 and will restart after a power failure.

Thanksfor your response. Is this a good choice in a much colder environment? Also, why this over a hanging unit heater?

 

[CNGsaves]

Think long and hard about ruling out radiant heat in Wisconsin. You have abundant and cheap natural gas so it would be no problem to keep whole structure toasty all winter on the cheap. At bare minimum, put all the pex pipes in concrete even IF you keep thinking you don't want radiant. I'd bet that future owners of garage WILL want radiant in Wisconsin.

 

[bedn0009]

CNG Saves. I think your logic is sound... but the math isn't adding up for me. Remember this is 1000 sq ft, plus a second level room that's 14 x 32:

$1000 to install the pex in the slab
$1000 to install the pex in the upper level
$7000-$10,000 for a boiler (please correct me if I'm wrong on this figure)

That's a $10,000+ install for a system that I cannot turn on in an "on demand" fashion.... which means it's going to be heating when I don't really need it, a fact that I think would negate any efficiency benefits.

That vs $1000 for a unit heater installed on the main level, plus TBD for the second.

I want to do in floor for the same reason everyone on GJ does anything ("Anything worth doing is worth overdoing"), but it's not adding up to me.

 

[Streetbu]

There is no reason to not use a regular forced air furnace. I do. I love it. I keep the thermostat turned all the way down, keeps my garage at 39 degree's. When I want to work, takes 25 minutes to warm it to 65. This past February I had a garage party. Got it up to 82 & it was only -14 outside I used a mobile home furnace so I don't have the luxury of nat gas. Uses about 5 gallons a weeks to keep it at 39 with the 16' door opening twice a day. The forced hot air is also good to dry the air out, especially if your dragging snow inside.

 

[Scott r c]

People don't typically use ducted traditional furnaces because it costs more, takes up more space, and being a garage, air distribution typically isn't a high priority.

There is nothing stopping you from going that route.

Given that you are potentially doing a living space above... you cannot (and shouldn't) share the same HVAC system between the garage/workshop and the living space.

I am using the same unit for my shop and office above. Its on separate thermostats with dampers.

 

[Radix2]

Maybe some more description about the spaces - first floor is garage - with cars, ect? - firewall between spaces, and sep air handling needed?
Second floor is shop, apartment, storage? Prepping for living space? Needs separate climate control or just spillover from first floor?
Maybe some thought if you want to redo the system over time or build now for final configuration?

I would consider direct vent or radiant ( fill with antifreeze if you want to shut down ) for first floor, mini-split for upstairs if it is going to be an apartment ( maybe a cast iron direct vent stove for the winter)

 

[theoldwizard1]

...I've decided against in-floor radiant... initial cost is too high, and I don't want to be locked into keeping it on all winter.

Most radiant heating systems use some type of anti-freeze so you do not have to leave it turned on all winter.

That being said, if the system has been off for several days and the floor is the same temp as the outside, it is going to take some time to bring it up to temp.

Radiant heat is also easy to expand to the second the second floor, even if you just use baseboard radiators.

I will run natural gas to hte building (along with electrical) and my ceiling height is 9 feet.

If A/C is a priority, you might consider a mini-split heat pump. Also expensive. It is hard to beat the operating cost of natural gas.

 

[pseudorealityx]

I am using the same unit for my shop and office above. Its on separate thermostats with dampers.

This isn't a good idea for a few reasons.

1) The air is mixing. Maybe you want your office to smell like oil/wood/paint/welding/whatever, but most people don't, and it can be dangerous in certain circumstances (carbon monoxide).

2) While your t-stats control the dampers, there's still a limit as to how much you can turn one down compared to the other.... ie, you cannot have your office at 72, and your shop at 40.

3) You're saying dampers, and I'm guessing you mean motorized dampers, but you should also have fire dampers.

 

[Reflex]

Bedn,

I realize that you've ruled out radiant, but it may be worth reconsideration. I'm not sure you're figures are right regarding the initial cost. I recently completed my 42 x 56 shop with radiant. The cost of my entire project was significantly less than what you've anticipated.

PEX into the concrete. Yes may be around $500. Barrier PEX can be purchased for 30 to 40 cents per foot (or less), but you'll have other costs. The biggest cost is the insulation that goes under the floor. Figure about a buck per square foot for the insulation.

You'll have the costs of the pump(s) and manifold(s) etc.

What really gets me, is I'm not sure how you're coming up with 7 - 10k for a boiler. A tank type or tankless unit can do the job for significantly less money. While there are additional steps or items that need to be used for this type of installation, the over all cost of using these items is far less than you've estimated.

Before others jump on me for suggesting these items, this is a Ford vs. Chevy type of argument. In other words, cast iron boilers, modcon boilers, water heaters, and tankless heaters all have their advantages and disadvantages.

What I find is that when somebody gets "uptight" about what MUST be used for a heat source, it's usually because they haven't had much experience or had a bad experience with something other than what they use.

The bottom line is that oxygen kills a radiant system.

If you keep the oxygen out of the system, most anything will work if sized and installed properly. This includes a tank type water heater. In addition, a tank type water heater is designed to work with DHW so it can handle oxygen. Lastly, even if your system is not "perfect", the limited amount of oxygen entering into the system won't effect the water heater since it's designed for a system containing oxygen (potable water). It's common for a tank type heater to last 20+ years in this type of system (if sized properly).

Tankless. The big problem here is pressure drop. Also, most tankless are too large from a BTU/h standpoint to operate efficiently for radiant. They tend to short cycle creating inefficiencies in both heat transfer and cycling losses. If the flow in your system is such that it meets the minimum flow to turn on the tankless unit (.6 gpm in most units), then your problem isn't as great. To overcome the sizing issue, some manufacturers make tankless units down to 140,000 BTU/h. While still oversized for your application, it's not as bad as using the standard 199,000 BTU/h units. Lastly, you can install a buffer tank (10 - 20 gallon) to nearly eliminate the pressure drop in a tankless powered system.

A.O. Smith and State both make side tapped tank type water heaters and also make tankless units that are approved for radiant heating. Your local codes should be consulted before using this type of system for radiant. In my area, there is no problem using a tank or tankless for radiant.

In any case, any of these units can be readily purchased for under $1500 at local supply house.

Best of Luck,

Reflex

 

[Jackfre]

Thanksfor your response. Is this a good choice in a much colder environment? Also, why this over a hanging unit heater?

I have to acknowledge my bias here as I was Rinnai's rep for 20 yrs and still consult with them. That said, I've heated my homes, garages, basements, new house and will be putting the EX38 in my new shop in August when it replaces the ES model. I estimate that 90-95% of those I sold in '91 are still in the field. These are quiet, cool to the touch, direct vent (supplied with unit), modulating gas and blower, simple install, built in programmable, self diagnostic and as noted reliable. Vent termination clearance to a window or door is 9". I always install mine under a window. I've sold over 210,000 of these in New England, with 70% of those in ME, NH & VT. They excel in a cold environment and the stat allows the 40* temp you want.

 

[theoldwizard1]

I have to acknowledge my bias here as I was Rinnai's rep for 20 yrs and still consult with them. ... I estimate that 90-95% of those I sold in '91 are still in the field.

Very impressive !

Any reason those unit could not be mounted on a bracket say 4-5' off the floor ?

What are the clearance spec for the outside vent ?

 

[Jackfre]

They can be mounted higher, but it is a heating appliance. Why mount it higher. You want heat at the floor. Nature says it will rise on its own. I can tell you that years ago I was welding new floor pans in an old car and while laying on a creeper it was really sweet having that warm air rolling across the floor under that car.
I post the clearances because many confuse the clearance requirements of a direct vented unit and a power vented unit.

NFPA 54, the Nat'l Fuel Gas Code says that a direct vent appliance less than 10000 but has a 6" clearance to a door or window. Less than 50kbtu is 9" and over 50000 is 12". It makes a difference if folks think it is a power vented unit which 3' above any air inlet within 10'.