thinking of using in-floor hydronic heat for my new garage/shop. anyone have any info or experience to share. I've heard you can use a hot water heater which seems to be a lot less expensive than the boilers I've seen. But, is that enough for michigan winters?

The amount of heat you need determines the heat source. Step 1, You MUST do a heat loss survey calculation.

A domestic water heater can sometimes be used, but since they are not designed for this, if done wrong they will fail long before the right choice for the project. There also may be code issues. If this is to be inspected, it may not pass with a domestic water heater placed into heating service. Gas water heaters, both tank type and on-demand, and the electric on demand heaters vary on their output and duty cycle, so one would have to be chosen carefully for the project to not attempt to run it beyond it's limits and kill it. The 4500W element in an electric tank type domestic water heater puts a little over 15,000 BTU per hour into the water. But these elements are probably not rated to do this on a continuous basis.

Yes, a water heater can cost a lot less than a purpose built boiler, but lots of headaches and burnt up heaters if you don't engineer it properly... If you have to replace it every other year, is it really cheaper?

SO measure the wall, floor, ceiling and opening areas.
Determine the insulation R value for each of these areas.
Calculate the total room volume and take a stab at the air infiltration rate(garage doors are notoriously leaky).
Determine the outside design temp for your area.
Determine the desired inside temp.

Take all that information to the Borst Engineering website and punch it into their free heat loss calculator. They have created a bunch of calculators free for personal use, they post here regularly under the user name SailawayRB. The instructions for the calculators are a must read, and will also probably help you get your brain around the heat loss problem. There are other calculators out there as well, but theirs is quite detailed and a good learning experience with the instructions. At any rate a heat loss calculator will help you to get an idea on how much heat you need to maintain a given temperature in the garage.

Every other year...riiiight.

We use a lot of water heaters for space heating. Particularly when DHW is needed.

Many garages have heat loads--properly calculated with a radiant specific heat load software--that are too low for the smallest condensing boiler and thus a poor choice.

We design many garage/shops with various HVAC equipment dictated first by a proper Manual 'J' heat load and second second by the intended use followed up by the available fuel sources.

If you want to attempt a DIY heat load your can try the real thing here https://www.wrightsoft.com/downloads/demo.asp We have been using Wrightsoft for radiant floors, walls, ceiling and snow melting driveways since 2006.

Thanks Ronmar and glad you find our DIY software useful! Based on requests, I recently refined our passive solar design software to calculate sunrise, sunset, first light and last light times. Some folks who live in mountainous areas (i.e., have significant terrain obstacles) wanted to know precisely when direct sunshine would reach and leave their building site at various times of the year. And then some folks who were interested in celestial navigation and astronomy subsequently requested us to also account for civil, nautical and astronomical twilight... Anyhow, we are happy folks find our software to be useful and we are also happy to refine it too...thank you!

If one wants to purchase professional heat loss analysis and hydronic radiant design software, we highly recommend Avenir HeatCAD and LoopCAD. The Avenir software has both the more accurate ASHRAE methodology and the simplified HVAC technician industry standard ACCA MJ8 methodology. The Avenair software is more competitively priced and far less prone to accept erroneous inputs and generate erroneous outputs than other professional software also approved by ASHRAE/ACCA. Brad McCrea also provides excellent customer support.

Badger, of course you can use a water heater if you do it right, and for a particular situation it may be a better more economical choice... I am sure you know how to, and have done it right using a water heater. Now imagine it done really really wrong, and the headaches that would cause...

Frank Miles -

The answer is, "it depends." Totally agree with Badger, a lot of times when you calculate the heat loads, the smallest boiler can be way over kill. Also, make sure you insulate the slab well and please consider using Creatherm Panels.

www.creatherm.com

...and I totally agree with Ronmar and I nearly always totally disagree with Badger.

Frank Miles, do you have to have Hydronic? There are lots of other competitive solutions that are cheaper on the short and long term, especially that it is a new built. Please check this video and our website:

https://www.youtube.com/watch?v=jJF5YwenuAg
http://rizeqco.com/radiant-heating-system

Our system will save you money on installation, operating costs, maintenance and on top of that if there is any shortage in electric supply, the thermal mass built under your garage's slab will keep you warm for at least 3 - 4 days.

feel free to contact us if you have any questions.

I agree with Badger......To heat the slab a hot water heater is the best choice(price, output, tolerance to design problems) It is just the better choice for DIYers....

But I would not do radiant in my garage unless I was planning on keeping it the same temp 24/7. It will take at least 6 hours to bring it up to temp in cold mich weather.

Natural gas ceiling heaters will heat the garage up in 10 minutes, and are cheap.

A boiler specifically designed for space heating is always the preferable solution if you plan to stay in the house any length of time. Unfortunately, there really aren't any good modulating condensing boilers suitable for very small heat loads. There are electric boilers that might be suitable, but at the expense of higher operational cost. However, if your heating load is low enough, your electric bill might be quite reasonable. You might want to consider a NextGen boiler:

NextGen Boiler

Going this path will save you the significant cost of having purchase a circulator pump, expansion tank, air vent, and differential pressure relief valve separately. A NexGen boiler installation is extremely DIY friendly, especially when compared to a modulating condensing gas boiler. The NextGen boiler also has a Summer mode that cycles the circulator pump, keeping it from seizing up...a common problem when the hydronic system has a significant period of non-use.

A question I have is can you get a NextGen system that will handle a whole house, good size garage, and possibly some driveway icemelt. We plan to have net-metered solar on our new home, so anything electric should theoretically be free as long as we get enough panels up there...

The NextGen boilers are available in sizes of 4 kW (13,652 Btu/h), 6 kW (20,478 Btu/h), 8 kW (27,304 Btu/h), 12 kW (40,956 Btu/h) and 14.4 kW (49,146 Btu/h). Whether any of these will work for you will depend on your heat load requirements. These boilers cost about $1,500. We have installed quite a few and they work very well. There is more discussion about NextGen boilers here:

NextGen Boiler Discussion

Re transfer plates vs gypcrete, it's important to distinguish between emitter efficiency and energy efficiency. You can mostly disregard the latter -- the heat in either plate-vs-poured is inside the conditioned space. So the questions are how much heat is going up rather than down and in what timeframe. And we aren't stuck with standard practices here because the OP is DIY.

Which is to say that it's quite easy to improve on transfer- plate efficiency. For example, use a inch of EPS to raise the floor level for pex and plates and float an engineered floor over it. You'll have R 4.5ish down counting the subfloor and R 0.5 ish up. As a bonus you'll get excellent soundproofing against impact noise heard in the floor below. Hardwood planks are more expense and more work. I glued a half inch of cork to the subfloor, then glued quarter inch underlayment to the cork and then oak planks to the underlayment. That amounts to R2.6ish down counting the subfloor vs R0.64 up, plus very good soundproofing against impact noise. The materials cost about $3/ft. I do just fine on 120-degree water. Your results will vary, but I suspect that closer PEX spacing can substitute for higher temps. You'll need to work out room-by-room heat loss and how fast the floors gain heat in a recovery scenario.

When we talk about about emitter efficiency, it is about what percentage of the heat provided to the emitter actually ends up getting to the intended living space. So emitter efficiency is partially about the ratio of the upward/downward heat transfer. As you increase the amount of R-value below the PEX or reduce the amount R-value above the PEX, this ratio increases...which is our goal if we care about emitter efficiency and minimal operating cost. Most good new construction HR designers like to see this ratio between 90-95%. Some compromises are made when accomplishing remodels.

The problem with anything other than fully concrete embedded PEX emitters, is that PEX heat transfer is badly degraded because of the lack of complete PEX circumference/length thermal contact. This is sort of the same reason we use thermal paste under our PC CPUs to ensure we can keep them cool enough. So emitter efficiency is also partially about how much heat can exit the PEX, get transferred to the emitter as desired and not go back to the heat source. Yes, heat returned to the heat source does not reduce the energy efficiency of our heating system by itself, but it does reduce the emitter efficiency. Reduced emitter efficiency always results in a higher required water supply temperature to satisfy the living space load requirements and this requires more fuel energy to achieve and this does reduce the energy efficiency of our heating system.

The lowest required water supply temperatures are achieved by using fully concrete embedded PEX emitters in lieu of above/below floor plate systems and maximizing the ratio of upward/downward heat transfer. The good news is that one doesn’t have to talk about this at all. One just needs to exercise good HR design software to get the precise answer for whatever one will be doing.

I get the impression that "badly degraded" can sub for "not ideal" in Sailaway's world. Then again, I meant my comment for loghomebuilder and put it in this thread instead.

DIY lives in its own world. If a heat loss analysis calls for pex 6 inches OC, or pretty much continuous transfer plate under the finished floor, well, at least the labor for all that piecework is free. By contrast, I wouldn't touch the concrete flatwork involved in gypcrete with a 10 foot screed. (The sleepers in the webpage that loghomebuilder linked are quite likely DIY aids.) And the problems are just beginning. Next up: waiting six months at least before installing hardwood plank and counting then on controlled moisture transfer.

And who is to say that his log house is not greener on a life-cycle basis than an ICF house? My oak plank floors were milled from the trees on the building site that had to be cut down. Log homes tend to be built in places where trees are plentiful, renewable and a major source of local income. ICF walls are a combination of petroleum-based foam and limestone heated to 1,800 degrees.

Let the guy build the house he wants in the way he wants it built. Then help him make it as efficient as possible.

It is important to put some numbers on these things. For one example of thick concrete slab vs mid-floor plates, I get 0% efficiency (btu delivered vs btu input) difference using electric heat, +2% using a condensing boiler and +9% using a ground source heat pump. These numbers (edit: effectively, as in $/year) go down once you account for the additional expenses related to high mass emitter under/overshoot and loss of setback ability (I get 5% eyeballing a Siegenthaler example). Your numbers will vary.

Warmboard has an example of exceeding gypsum efficiency, even when the gypsum tube spacing is doubled. I expect that good plates with ~100% coverage (data is often for < 75%) would also match or exceed gypsum.

Back to the OP: For a non 24x7 heated garage, I'd use overhead radiant.

Absolutely, one should always build what they want. There is no question that a structure constructed and heated from on-site renewable carbon-neutral logs is greener than everything else...except perhaps for a tent.... Which proves that you can have a very energy inefficient building, but still have a very green building.

There is no question that Warmboard is a very good product. It offers much better PEX thermal conductivity than plate systems. Claims are always plentiful, but you have to actually run the numbers and actually accomplish many installations to know the truth.

By the way, setback doesn't affect efficiency at all. Setback may only reduce operational costs by trading it for a lower indoor temperature for some period of time. If you turn off the heating system, you can reduce operational cost to zero...but the building or heating system efficiency doesn't change...

It would be foolish to use setback with a high thermal mass HR system. A high thermal mass HR system excels at keeping the indoor temperature constant and rock stable, especially if you have a low load energy efficient building that is insensitive to outdoor temperature changes.

Posted By sailawayrb on 25 Aug 2016 11:56 AM
Absolutely, one should always build what they want. There is no question that a structure constructed and heated from on-site renewable carbon-neutral logs is greener than everything else...except perhaps for a tent.... Which proves that you can have a very energy inefficient building, but still have a very green building.

There is no question that Warmboard is a very good product. It offers much better PEX thermal conductivity than plate systems. Claims are always plentiful, but you have to actually run the numbers and actually accomplish many installations to know the truth.

This follows my real world experience in the field and at home. Nicely put.