Gas Hydronic Heating Options

[Black_Z28]

Hello, I have a question regarding my options for natural gas hydronic heating for my garage.

A little back story, I have a detached 26x28 garage that is currently heated by a electric hydronic boiler. It works great, except the amount of electricity it uses is ridiculous. I'm averaging about $300/month to heat my garage in the winter months. So, I'm looking into switching the boiler over to gas. I have a HVAC company quoting me the cost to run a natural gas line from my attached house to the garage.

But, my question, I'm not really seeing many options for gas fired boilers. It seems most that I find (and I could be looking for the wrong thing) are whole house hot water heaters. Now, I realize these two are probably pretty much the same, but I assume there are some differences. One being the activation of the recirc pump.

So, does anyone recommend a brand or a place to purchase the boiler? I plan to have the HVAC company do the gas line to the garage, but I can easily install the boiler myself.

My other option would be to leave the current electric boiler as is, still run a gas line, and just installed a drop down unit heater, like a reznor. Which is in my attached garage. Which works well, but it's definitely a different feel of heat. I really do like the heated floors in the winter when working on the car or other projects. So, I really would prefer to just remove the electric boiler and go to gas.

Thanks

 

[HoosierBuddy]

When faced with the same issue, I went with a high efficiency modulating wall boiler. "Modulating" means it can run the burner up and down as needed to supply more or less heat. That being said, you may struggle to find one small enough for your needs, as they are designed (typically) to heat a whole house.

What is the KW rating of your current unit? That would allow us to back into a BTU/hour rating that would be equivalent.

Also...I don't "hate" your idea about using a hanging NG heater. That's a viable option too.

Phil

 

[kj_mustang]

Depending on amounts of insulation installed in the building, under and around the edge of the slab, and the layout of the pex in the floor, you may find that gas heat isn't any cheaper to use. Have you compared the cost per btu required to heat the building for each type of fuel? Electric boilers are pretty efficient so it may be other factors and not just the cost difference between the two fuels.

 

[Jackfre]

There are many of the referenced "wall hung modulating boilers". This is a regular question on this site and many have had success with the Water heater type units like the Takagi. Yours is a small space for radiant and if your slab edge and insulation package is up to specs you should look at a very low firing rate of the boiler. many will modulate down to around 10kbtu. Analyze your piping lay-out. The wall hung boilers do their best work when piped as a primary/secondary lay-out. Frequently the boiler will have the primary circuit built into the boiler itself. One of the best features of wall hung boilers is they generally (check this out) come equipped with the outdoor reset (ODR) program that allows you to select parameters for it operation. If you are squared away on this you can make that boiler sing any song you want it to. Before spending any dough, you may, if your slab edge insulation isn't right be pumping $200 of your $300 out the edge of the slab. A couple years ago I was asked to look at a local ladies radiant heated home. It was a beautiful home with a great deal of expensive landscaping up to the house. There was no slab edge insulation and it was costing her enormous sums to be comfortable. When faced with the expense and inconvenience of proper edge insulation she abandoned the radiant. An infra-red gun is an effective tool for this.

 

[Black_Z28]

When faced with the same issue, I went with a high efficiency modulating wall boiler. "Modulating" means it can run the burner up and down as needed to supply more or less heat. That being said, you may struggle to find one small enough for your needs, as they are designed (typically) to heat a whole house.

What is the KW rating of your current unit? That would allow us to back into a BTU/hour rating that would be equivalent.

Also...I don't "hate" your idea about using a hanging NG heater. That's a viable option too.

Phil

My current unit is a wall hung and has dual 5500Kw elements. I have tested both elements are they both draw ~22amps. So, they are drawing what they should be drawing.

I will have to check out the edge of the slab insulation. Although, I won't be able to check this until the temps drop.

I'm honestly not sure on the piping layout. I'm sure I could crank it up, and use a infrared gun to see where the concrete warms up first. I just know my slab has 3 runs of pex pipe. Since there's a 3 way manifold going into the concrete.

NG is pretty dang cheap in my area, so I'm guessing it will be cheaper to run NG vs. electric.

 

[Jackfre]

100kbtu/therm of NG at 95% with gas boiler. 95kbtu net/3414 btu/kw=27.83 kWh to equal 1 therm of NG.

 

[Black_Z28]

Alright, I checked my bills from last winter.

For electric, I see:
$.105/kWh

For NG, I see:
$.4987/therm

Also, in the dead of winter I was seeing about 2500 kWh of consumption. Now, in Oct, where I wasn't using the AC or heater in the detached, I was seeing about 450 kWh consumption. So, I'm guessing the garage is using around 2000 kWh/month.

Jackfire, looks like it cost almost 6 times as much to for electric then gas in my situation.

$.105 x 27.83= $2.92

Am I correct with that??

You guys are being very helpful.

I did see Takagi while doing a search, but had never heard of that brand, and wasn't sure on the quality. I'll look into those units further. I'm guessing a 80K unit would be sufficient for my space?

 

[Jackfre]

Gas is almost always cheaper than electric. The Takagi is a water heater approved for space heating. It does not have an internal pump and perhaps most important it does not have the ODR. The ODR really improves the operation of the boiler by adjusting output temp depending upon an outdoor sensor, as well as giving you other programming and operational features. You do not need the same temp water to heat at 30* as you need at 0*. Going on the water heater side you give up the boiler features, but it will make heat. I mentioned it as there have been guys here using them and liking them. I would not heat with a water heater, but you get to make those choices.
You do not tell us where you are, so I will ask the question. Are you in Minot or Miami? It matters. I would say that you are over on your 80k sizing by almost 3X. You need a modulating boiler in the 10-50 or 60kbtu range. Don't oversize it. With modulating equipment the lower range is more important to you than excess capacity. At your flow rate the slab can only take so much heat anyway, so you end up with high return water temps. Then you are trying to control everything with the modulation on the burner and my experience says that is not a good long term solution. The boiler I've been using has a modulating circ in the boiler. The circ modulates to get the max out of the temp before the burner modulates. Nice and tight control and operation.
It is possible that depending upon your piping lay-out, and you have to do the pressure drop calc to determine this, that you may be able to simply use a straight thru piping system eliminating the need for primary/secondary piping. I did a system on a very small radiant job for a friend and we were able to use the internal boiler circ to drive the system. It worked very we'll for him. He had been using a water heater on that for years. He sits and watches it. I have been suggesting hobbies for him. I'm not worried about him yet, but have told him to just go lay on the kitchen floor.

 

[Black_Z28]

Sorry, I should have mentioned my location.

I'm located in Central MN.

I figured it would be much cheaper I know others that run gas and they're astonished how much my electric bill was this last winter. Which got me thinking about going to a gas boiler.

So when you go the water heater route, is there controls for my external pump? Right now, when the stat calls got heat, the pump turns on, and then the elements start heating. It achieves the set point and shuts down.

At work we have a exterior loading dock. The pump for that continuously runs and the boiler cranks on when the fluid temp drops to the set point. Is either a better situation?

Three local Menards does have a actual radiant boiler in stock, it's 115k and I believe 83% efficient. I assume the unit is overkill as well.

 

[HoosierBuddy]

11,000 Watts = 37,500 BTU/hour

You would need to upsize from there for the loss of efficiency. 10 to 20 % based on what you choose as a boiler gets you to around 45,000 BTU/hour...so if the current electric boiler can keep up, that gives you the minimum size NG boiler you might use.

Your cost comparison is OK up to a point, however .4987 per therm seems too low. I bet that number doesn't include all of what you are paying.

For both your electric bill and your gas bill, go back and just divide your cost in dollars by your usage. That will tell you the actual cost per unit of energy for each.

Then increase your NG cost/therm by 10% to cover the fact electricity is going to be 100% efficient at the point of use vs Natural Gas which is going to be on the order of 90% efficient (might be more...might be less based on your equipment choice). That will give you a better picture of how much you can save.

My WAG (wild-a$$-guess) is you'd be looking at saving about 2/3 by switching to gas vs electric resistance heating.

If you could do more with insulation, obviously you could save more.

Phil

 

[Jackfre]

"You would need to upsize from there for the loss of efficiency. 10 to 20 % based on what you choose as a boiler gets you to around 45,000 BTU/hour...so if the current electric boiler can keep up, that gives you the minimum size NG boiler you might use."

Phil, I think that is the maximum size vs minimum.

 

[Bills Tools]

Get a lockinvar Knight boiler


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[Black_Z28]

Alright, I've been doing some looking around.

Mainly at supplyhouse. And, I''l apologize for my ignorance on this, but I'm looking at different models from Takagi, which was mentioned earlier in this post.

So, I'm not finding a lot of options in the 40-60K BTU area, but could I get a modulating tank less water heater, so it can determine the amount of fuel to use?

Also, could I get away with a non-condensing unit, so I do not have to deal with draining? I have a drain in my garage, but it's in the middle, and might be complicated to get the condensing fluid to.

So, here's what I'm looking at.

This unit:
https://www.supplyhouse.com/Takagi-...ng-Indoor-Tankless-Water-Heater-6-6-GPM-NG-LP

Also, this relay to activate the pump via my thermostat.
https://www.supplyhouse.com/Taco-SR501-4-1-Zone-Switching-Relay

So, if I'm understanding this correct, the thermostat calls for heat by signaling the relay, it activates the pump, which then causing the tank less heater to fire, because the flowing water is cooler then what normal hot water should be. Is this correct thinking on this?

 

[Black_Z28]

Here is another option I found before, just not sure on the quality of the item. But it is a modulating unit. So this might be a better option then the Takagi.

https://www.menards.com/main/plumbi...791-c-8519.htm?tid=8281999769277035196&ipos=3

 

[Black_Z28]

I guess the next question would be, am I better off just buying one of these pre-built control panels for a micro boiler? Currently, my system just has the single pump, an extension tank, which I think I should respect anyways and a pretty old stat. So I would be replacing the tank and stat, I would also need the Taco relay for the stat to activate the pump. And I believe I would need to add a secondary pump, because the boiler I linked is a modulating pump.

https://www.menards.com/main/plumbi...456-c-8521.htm?tid=5361038026903596292&ipos=4