9kW Boiler/Tankless Recommendation Please

[Cougfan]

I am trying to figure out what model of electric water heater I should get for my in-floor heat. I have done a ton of research for a recommendation on one and, believe it or not, I have had a hard time finding straight forward recommendations. I have done the heat load calcs to the best of my ability. I will need about 28k BTU/hr to heat my shop to the desired temperature. I have also calculated that I will need a minimum of ~2.5 gpm of flow based on 5 loops of ~420’ of ¾” tubing.

I have read a lot of debate between the electric tankless water heaters and electric boilers, but for the life of me, I don’t know what the difference is between them. Is there a difference? I have looked at names like Argo, Electro, Hydro-Shark. Are all of these the same thing, relatively? How are they different than a Rheem tankless water heater that sells for significantly less.

The hydro shark is cheap but requires P/S pumps, but that has also been debated on this forum. Is a P/S pump necessary or is it a manufacturer CYA?

Just by looking on the internet, it looks like I will be spending between $800-$1500 if I go for a “boiler”. If I go for a tankless water heater, I will be spending $200-$400. Does this sound about right?

I know it seems like this topic has been beaten to death, but for whatever reason, I need more help.

 

[anthony666]

a tankless water heater is designed to take low temperature water, quickly heat it to a usable temperature and then send off to a tap or appliance never to be seen again .. open loop

a boiler is designed to have warm water returned to it and bring it back to design temp knowing full well the same water will be back again .. like a mom waving at her kid on a ferris wheel .. closed loop

 

[powerhound]

I too am doing the same search. I too have heard names like Electro. My question is where did you find the info to do the heat loss calcs?

 

[Cougfan]

I googled "Heat Loss Calculation", and clicked on the 4th result which is titled "5-Step Heat Loss Calculation". It is from a reputable PEX supplier. It steps you how to run the heat loss calcs. After that it is just a matter of plugging the information into a spreadsheet. Let me know if you have any more questions. I am no expert, but I may be able to help.

 

[Highbeam]

Though I'm a UW alumni, I am right here with you on this issue. I have ran the 50 amp circuit to the manifold location and I will be selecting a heat source that is 7000 or 9000 watts. Here's what I've found.

Boilers have bigger connections and plumbing so you'll have less head loss through them. Sure the tankless guys say they can flow 3 gpm but that is when you can provide a huge pressure differential through the heater such as going from 60 psi to 0 psi at the tap. Much head loss means bigger pumps and more losses for pumping.

In theory, the boiler is more robust and with parts that are more easily replaced but I don't buy that.

Also, in theory, the boiler could be equipped with outdoor resets, stages of output, and even time of day controls to take advantage of lower power rates at night. None of that freaking matters when you're heating a slab and you can do most of it with a decent thermostat.

Heating with resistance heat actually allows for a simpler system since you don't care if it short cycles.

Also, on the boiler, it will be rated and listed as a heater for this application. In the event of a fire, it would be nice to have a heater that was being used per the manufacturer's requirements.

 

[Cougfan]

Highbeam, I can overlook the small detail that you are a mut at heart .

It sounds like we are in similar spots. I haven't made up my mind yet on which way to go. I will be putting in my floor late summer, and will probably be hooking up the heater this fall. If you think about it when the time comes, let me know what you end up going with and if you like it. I will do the same.

 

[powerhound]

I found that site and one other once I dug a little deeper. One says, 38,000 btu and the other says 40,000 btu loss, so it looks like I'll be needing to go quite a bit bigger than what I had planed for a boiler size

 

[Highbeam]

When I did the pexuniverse 5 stepper it said I needed 29k btu which is somewhere around 9000 watts.