A Different shop heating idea

[Perry Holbrook]

I know it's hard to think about shop heat right now, but I have been toying with an idea that I would appreciate some opinions.

A few years ago I picked up a hot water unit heater with a fan that was used in a warehouse and have wanted to use it to heat the shop next winter rather than the kerosene heater I now use. My idea is to install a standard household electric water heater, circulating pump, expansion tank, the unit heater, thermostat, etc as my heating system. A pump like the one used in solar panels could circulate the water thru the heater and return it to the tank. Pipe runs would be very short as I would mount the heater directly over the tank.

Those hot water heaters have 2-4.5 kw elements in them. 9kw should heat the shop just fine. Right now electric and kerosene cost about the same per 1000BTU.

Anybody see something I'm missing. Perry

[Don Baer]

It should work. Radiator have been used in houses for years. I don't know how efficient it would be compared to direct radiant heat where you just use the electricity to heat the elements. I don't think it would be as effecient but hey I'm not an HVAC guy.

[Lee DeRaud]

What Don said.

Something else to consider is that this system will take up a lot more space than simple electric radiant heating elements: the radiators themselves are larger (unless you go with in-floor radiant heat) and you also need to have space for the water heater and pump.

I don't know what the winter climate is like in that area, but have you considered a straight solar-panel system?

[Carl Eyman]

If you allow the hw heater to always have a full tank of hot water, This might have a faster response time than direct electric heating. That resevoir of heat represented by the 50 (or so) gallons of hot water might be an advantage. Hot water heaters tend to be pretty efficient especially as any heat lost by your system will go right where you want it anyway.

You have the thermal efficiency to think about. By this I mean the efficiency of heat transfer is [T(1) - T(2)]/ T(1) where T(1) Is the temperature of the heat source and T(2) is the temperature of the object being heated. (T in both cases is absolute temperature) Since T(1) in an electric space heater is much higher than hot water, the difference in temperature between the two is much higher and thus the thermal efficiency greater in the case of direct heating.

I would appreciate any corrective comments from those more knowledgeable than I.

[Don Baer]

Carl,
You are making my head hurt. It's been to long since I studied thermodynamics..:confused:

[Jeff Horton]

A few years ago I picked up a hot water unit heater ....

You found a unit that heats hot water?? :)

Sorry, couldn't resist. Going back to my cage now.

[Mike Henderson]

Regarding thermal efficiency, it seems to me that whatever power you put into it will wind up in the shop as heat since all of the heating system elements are completely in your shop. There's no where else for the heat to go.

So if you have 9KW elements, the BTU/hr into the shop will be almost 31K BTU/hr (watts times 3.413).

Mike

[Don Baer]

Ya know mike your probubly right now that I think about it. I was thinking in terms of vented water heater like the gas kind where you vent the flame to the outside, not electric. I guess you don't vent the electric ones.

[Mike Henderson]

As Carl pointed out earlier, the biggest problem will be the lag time from the time you turn the system on to the time you start getting usable heat because you have to heat a big mass of water before you start getting any heat into the air. If you leave it on all the time, you will not have that problem.

If you do shut it on and off, you will also 'lose' some heat because the water will hold a bunch of heat and dissipate it after you leave the shop, unless you remember to turn it off some time before you quit work.

All-in-all, I think a direct electric heating element to air heater would have a quicker response time, and take less space in the shop.

Mike

[J. Scott Chambers]

Depending on the size of your garage, the outside temperature in the winter, the inside temperature you want to maintain, U-value of your walls, the size of the unit heater and airflow from its fan, it might work, but I doubt it. You'd need a water heater big enough to keep up with it.

Most residential water heaters have two elements, but only one works at a time. You can get them with simultaneous elements, but they're more money, and will require a bigger breaker, etc. Not too mention you may need to crank the water temperature up a lot (most hot water heating systems work on 160-180 degree water), which will reduce the recovery time on the water heater.

It may work, but I lean more towards getting a small, residential boiler.

Good luck.

EDIT: There are systems the used this idea, the Apollo systems come to mind. But they were used in insulated homes, but a similar concept.

[Perry Holbrook]

Thanks for the thoughts so far. A little more of my thinking. I have a hot water system with the old cast iron radiators in the house. That system works like this. It has an oil fired burner. There are 2 seperate control systems. The one on the boiler senses the water temp and turns the burner on and off as needed. I have it set for a water temp of about 150 deg. The programmable t-stat in the living space, turns on the circulating pump to maintain the proper space temp. The system works fine, but it is not feasible to connect more piping and run the water out to the shop.

So for the shop I would do basically the same thing. The water heater would stay on all the time to maintain the water temp with the built-in t-stat. A circulating pump and the unit heater fan would be controlled by a programmable t-stat. Should work just like the house. Electric water heaters run at 92% efficient. Since it is a closed loop system the thermal efficiency of the unit heater does not really have a great impact. As someone said, any lost heat goes into the space I'm trying to heat.

I'm in the shop about 60 hours a week. A working temp of 65 and a night time temp of 45 with the programmable stat seems realistic.

I know an electric boiler may be a better choice, but I'm not so sure it would be that much better. They are designed for multiple radiators and more complex systems. This would be a tank with a small pump, the unit heater and about 10 feet of pipe total.

Does this make a difference for anyone.

Perry

[Joe Mioux]

Hi Perry:

So you have a Heat Exchanger and you want your heat source to be a water heater.

It will work and it will work well!

I have a heat exchanger in one of my garages at work. Mine is connected to a boiler, but that is what a water heater is anyway.

If you keep your garage thermostat set around 45 50 all the time, getting it to room temp will not be a big problem. It doesn't take any longer this way than with a furnace (once the heat exchanger turns on) There is a lag in time with the heat exchanger, you need to get the water in the lines hot enough for the fan to turn on.

Joe

[Bruce Wrenn]

I know it's hard to think about shop heat right now, but I have been toying with an idea that I would appreciate some opinions.

A few years ago I picked up a hot water unit heater with a fan that was used in a warehouse and have wanted to use it to heat the shop next winter rather than the kerosene heater I now use. My idea is to install a standard household electric water heater, circulating pump, expansion tank, the unit heater, thermostat, etc as my heating system. A pump like the one used in solar panels could circulate the water thru the heater and return it to the tank. Pipe runs would be very short as I would mount the heater directly over the tank.

Those hot water heaters have 2-4.5 kw elements in them. 9kw should heat the shop just fine. Right now electric and kerosene cost about the same per 1000BTU.

Anybody see something I'm missing. Perry The elements a sequencial. Means either one or the other is on, but not both at same time. 2X4.5=9 9KW- 9000watts. 9000/230=39.1 amps. This is too large a load for #10 wire, so elements are sequencial to prevent oveerloading. When heater ifs full of cold water, upper element comes on. As temp. rises, upper shuts off and lower comes on.

[Perry Holbrook]

Bruce, can I rewire the elements so they work together. Wire size is not a problem. I'll run whatever is necessary. I've already wired a 40 amp and a 50 amp kiln in the studio.

Perry

[Robert Mickley]

It should work just fine, Of course the best way to get the heat in the shop is to heat the floor. Which is my goal.

As for heat loss, its not as bad as you think.
My outdoor boiler is 60 feet from the house. uninsulated lines burried 3 feet deep. Water temp drops 1 degree from the boiler to the house.

My heat exchanger is rated at 140,000 BTU's at 180 degrees. Temp coming out of the exchanger is only 10 degrees cooler than going in. I try to keep the water temp at 140-160Degrees. I only burnt 4 cords of wood last year.

Buy a circulation pump for a boiler system.
Mine was only $125. IF you go through the efort to heat the floor as opposed to a heat exchaner and a blower there are pros and cons.

Con is slow recovery times
Pro is it heats the objects in the shop not just the air. My neighbor has a heated floor in his truck shop. He can park his and his sons tri axle dumps in there in the winter. By the next morning all the ice and snow is melted off of them and the floor is dry. The other advantage is you can run cooler watertemps since the whole floor is warm and all the heat radiates up from there.

[Frank Hagan]

I know it's hard to think about shop heat right now, but I have been toying with an idea that I would appreciate some opinions.

A few years ago I picked up a hot water unit heater with a fan that was used in a warehouse and have wanted to use it to heat the shop next winter rather than the kerosene heater I now use. My idea is to install a standard household electric water heater, circulating pump, expansion tank, the unit heater, thermostat, etc as my heating system. A pump like the one used in solar panels could circulate the water thru the heater and return it to the tank. Pipe runs would be very short as I would mount the heater directly over the tank.

Those hot water heaters have 2-4.5 kw elements in them. 9kw should heat the shop just fine. Right now electric and kerosene cost about the same per 1000BTU.

Anybody see something I'm missing. Perry

Yep, it will work. Make sure you have the recommended pressure relief valve on the hot water heater tank (they usually come with them). But you have the other components identified.

The only real advantage I see is that there is no added fire danger from red hot electric elements. I've always thought that would be a dangerous combination in my shop, since I'm a messy woodworker.

My company makes "fan coil" units that are essentially radiators with a fan behind them. Hot water circulates in them and the fan blows air through the radiator portion, and the heat transfers from the water to the air. You supply the hot water, and the fan coil unit supplies heat to the room. Google "fan coil" for links to the stuff available.

If you are keeping the shop heated all the time, the idea that the losses from the hot water tank into the room help makes sense. That's not true if you just heat up the shop for use, then let everything cool off.

So you are getting nearly 100% of the heat you generate, rather than the 80 - 90% a gas fired unit usually gives (some go higher but are more expensive).

[Phil Maddox]

It sounds like you don't want to go this way but why do you say that you can't use your existing boiler for the source of hot water?

This is exactly the system I have in my shop. My house's boiler provides hot water to a fan-coil unit in my shop. Works great.

There is a bit of piping and a zone valve but not that big a deal.

Good luck.

[Perry Holbrook]

Phil, the house is 75 years old. With the original piping design, no zone control except hand valves at the radiators. The t-stat calls for the pump and the water circulates through out the system. There are a couple of valves in the system that seem to be there to help balance the water flow. I've never touched them and frankly I'm afraid too for fear they may start leaking or the system may go unbalanced. If I were to use this system for the shop, I would need a seperate pump and somehow tie it into the boiler. I think it will cause problems for the existing system, that is working just fine the way it is.

Another thought is the oil boiler is probably running at 75 to 80% efficient. The electric for the shop should actually be more cost efficient.

Since I've already got the "fan coil" heater, I think I can probably put his whole thing together for around $400. Fits the budget and will be a lot better for my health than the kerosene heater I now use.

Just for information, I also plan to use some of the waste heat from the kilns upstairs to assist heating the shop and a propane blacksmith forge will be added to the metal shop downstairs that can also help with the heat on the coldest days.

Perry

[Phil Maddox]

You have a good handle on what your situation is. If you are using a water heater, I would suggest one with a high rate of recovery with the smallest tank you can find. This would reduce the standby loss of the system, but allow it to come up to temperature pretty quickly.

What type of pump would you use? I love the Taco 007 series, they last forever.

Good luck!

Phil

[Perry Holbrook]

Thanks Phil, I'll take a look at that pump. Actually, there is a pump of that auction site that is for a HW solar system with a temp controller that I'm also looking.

Thanks for all the input, I think I'll give this a try.

Perry

[Gary Curtis]

I installed hydronic heating systems in two homes. Did it myself. Get the catalog from this company 2hsc.com . They sell everything and the catalog includes a tutorial on heating, energy specs and the water circulating equipment.

In my brand new home, I opted in the shop for a 240v. portable electric heater. Slight danger of sawdust in the heater catching fire, but I blow it out with air every few days. We get winter temps hovering at freezing, but the one heater brings the shop up to 45-50 degrees in under 15 minutes. And, I can move it around. The room is well-insulated.

Available at hardware stores for about $130 on special order. My rationale for it was that electricity in Trinity County Calif. only costs 6.3 cents a kilowatt hour. A hot water circulating system is a bit complicated (and expensive) for a shop, and you don't need the advantages of no ducting and invisible heat source.

If you do the hydronic route, buy the cheapest water heater. I paid $2000 for one boiler and $3500 for the second. And you don't need either the capacity or the features of either. Most suppliers will do the energy calcs for free so you can size the power requirements on the heater/boiler to the room, and thus save money.

Gary Curtis
Weaverville Calif.