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Another tankless water heater replacing boiler thread

I might add, instead of installing a "Well" type t-stat probe for the return glycol temperature, it would be a lot more simple to just strap on the temp probe to the copper pipe and insulate it. Gets rid of a solder joint and would be just as effective!
 
2Biz said:
The only thing I would have done differently is put in a domestic circulator to keep the HW hot to minimize the amount of time it takes to get HW to the faucet or shower head. He might have wished he would have done this with the install.
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2Biz & others,

This Navien device appears to very much simplify (no nee to add add'l piping) keeping the water temperature continuously primed. I am not sure but with a little finesse maybe it could be adapted to other systems besides just Navien.
 
2Biz said:
My neighbor is building a "Barndominium" on the property right behind my house. He installed floor heat in the slab and put in one of those Navien Combi units for the floor heat and domestic HW...It uses a small pump inside the heater that supplies return glycol to the heater, the same thing as my (2) Taco 013's...Opening it up, it is one sophisticated piece of machinery! For a CW, I don't know if I'd like all my eggs in one basket. So far his is keeping the living space at exact setpoint on the t-stat (air). The only thing I would have done differently is put in a domestic circulator to keep the HW hot to minimize the amount of time it takes to get HW to the faucet or shower head. He might have wished he would have done this with the install.
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I have 3 Navien heaters for hot water, then have a single Combi unit for the floor heat and HW. The Combi acts as the master unit and will throttle down the floor heat if it needs to produce more HW. The other 3 units should more than handle all the HW so I'm hoping the Combi will just throw everything at the floor heat.

Thanks,
Lighthouse
 
I didn't get a chance to talk to him myself (talked to my general contractor) but apparently now my plumber doesn't like the idea of two tankless water heaters for the floor heat. He talked to several suppliers and manufacturers and they say the tankless water heaters will short cycle all the time and the temps won't be very high so the life will be shortened. He said going with a boiler will be better and will cost about the same. I'm not sure what boiler he is looking at but if I compare efficiency and BTU input I'm seeing they are more like four times the cost. Also if you narrow it down to wall units (I'm looking for floor space) there is not much of a selection. I have not seen the install price yet but I'm sure it is ugly as I'm almost always surprised how much stuff is these days. I wish I would have done this myself several years ago but now there will be inspectors in there checking on the rest of this big project.
 
So I think the "General Contractor, suppliers, and manufacturers" needs some schooling! Although if the suppliers and manufacturers only handle boilers, then you know why they think the way they do!!! LOL...Making claims that demand heaters won't last because of short cycling? I wonder how many times a demand heater cycles a day when used in a household of 4-6 people?! If worried about short cycling when used for floor heat, a simple T-stat on the return that has an adjustable differential will control cycle length on the heater! I set mine to 15° differential to control cycle time....

Ourtown, I thought you already put in tankless for floor heat? Maybe thinking about someone else on the forum? Agree with you, boilers are more than 4x that of a demand heater. The last time I looked on Supplyhouse.com, My 199k Takagi was just over $1200. I'm on year 11 with it now! BTW, if you keep any type of heater/heaters under 200k, from what I unsderstand, you don't need to have a Boilers License to install or operate.
 
2Biz said:
So I think the "General Contractor, suppliers, and manufacturers" needs some schooling! Although if the suppliers and manufacturers only handle boilers, then you know why they think the way they do!!! LOL...Making claims that demand heaters won't last because of short cycling? I wonder how many times a demand heater cycles a day when used in a household of 4-6 people?! If worried about short cycling when used for floor heat, a simple T-stat on the return that has an adjustable differential will control cycle length on the heater! I set mine to 15° differential to control cycle time....

Ourtown, I thought you already put in tankless for floor heat? Maybe thinking about someone else on the forum? Agree with you, boilers are more than 4x that of a demand heater. The last time I looked on Supplyhouse.com, My 199k Takagi was just over $1200. I'm on year 11 with it now! BTW, if you keep any type of heater/heaters under 200k, from what I unsderstand, you don't need to have a Boilers License to install or operate.
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Still have no tankless water heaters installed for DHW or floor heat. I have done some research on boilers vs water heaters for hydronic heating and did not see anything really profound.
 
OurTown said:
I didn't get a chance to talk to him myself (talked to my general contractor) but apparently now my plumber doesn't like the idea of two tankless water heaters for the floor heat. He talked to several suppliers and manufacturers and they say the tankless water heaters will short cycle all the time and the temps won't be very high so the life will be shortened. He said going with a boiler will be better and will cost about the same. I'm not sure what boiler he is looking at but if I compare efficiency and BTU input I'm seeing they are more like four times the cost. Also if you narrow it down to wall units (I'm looking for floor space) there is not much of a selection. I have not seen the install price yet but I'm sure it is ugly as I'm almost always surprised how much stuff is these days. I wish I would have done this myself several years ago but now there will be inspectors in there checking on the rest of this big project.
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These are my NTI wall mount boilers, I have a third in my house. The one in my house was installed about five years ago and has worked flawlessly at about a third the cost of my old one.
 

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HeyVern said:
These are my NTI wall mount boilers, I have a third in my house. The one in my house was installed about five years ago and has worked flawlessly at about a third the cost of my old one.
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Very nice Terry Towel Rack! :D
 
OurTown said:
Those are really pricey but not out of line for a boiler I guess.
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Definitely more than a water heater, the one in my house works so much better than the old original 1950 unit that was in there and costs a whole lot less to run.
 
HeyVern said:
Definitely more than a water heater, the one in my house works so much better than the old original 1950 unit that was in there and costs a whole lot less to run.
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Are you saying that you just replaced a 73 year old water heater?
 
I was looking at the old boiler valve today and it has adjustment knob on it and was set at 4 or 5 (hard to tell) out of 10. Does that mean that the boiler was only running at 40 or 50% of the total rated input? If so then it was heating my 3,600 square feet on about 300K BTU or so.
 
Anyone thinking of getting a ebay chinese water heater, gutting the flow restrictions, and just letting it rip below 32*F my boiler despite little use, Has rotted away. Haven't had a chance to pressure check the loops yet. But all I'm looking for is to keep the bay floors from turning into a giant sheet of ice. Not sure if a boiler needs to be super overpowered and cycled to get that water moving towards the drain, or if a slow steady push back from the little train that could. I'm pretty sure the next cold spell of 24hr+ of below zero im going to blow down and shut down. $0-$3 a day isn't worth it. But for the occasional 10 below night a little heat atleast to thaw the mud so I can scoop it out would be nice.
 
I don't think a "Cheap" chinese heater wouild be a good idea. Here is a thread I started about 11 years ago in which others have followed suit. An alternative to expensive Boilers is to install a NG Demand Heater. The 199K BTU Takagi I installed is just a little over $1200 now at Supplyhouse.com and has been in operation since I started that thread. I've seen minus 15 degrees since then and this heater still has capacity left to cycle on/off and keep bays ice free. Thats at 105° output temp of the heater...You might pick up some good ideas from reading through the thread.

(2) Tankless Water Heater For Floor Heat | Car Wash Forum
 
2Biz,
How would you envision the plumbing, pumps and controls for a FH system for something larger than a 3 or 4 bay where you’re not going to get away with just one Takagi or whatever demand heater? Main loop going to and from the loops wouldn’t change….appropriate size pump running constantly below 35f. But how would the secondary plumbing for the two demand heaters be plumbed in? Would
it simply be the same as yours, but after the pumps, it would tee to the two heaters?
 
Good question...I found a very good video showing how to plumb multiple heaters into the main floor heat loop. It takes him 2 minutes to explain what would take me a lot longer here on the forum! The video is how I would do it except for one change. Instead of running the pumps in parallel like in his first diagram, I would plumb the heaters like I have mine in series to get double the pressure. You would tee between the pumps and heaters so both heaters see the same higher inlet pressure. MOST of these demand heaters get their throughput based on the inlet pressure. With (2) 013 Tacos in series, I get 40psi and 6gpm throughput...(1) Taco 013 and I got 20 psi and 3gpm output both at 105° temp output...The resulting differences was exactly like what was documented in some of the online publications I found. Pumps in series multiply or add the pressure of each pump to get final output pressure. Pumps in parallel has more volumn but output pressure is same as one pump.

In the video, he shows 2 ways of plumbing (2) heaters and explais how the first diagram is the best way. He aslo ecxplains having the heaters under the main piping loop? On mine, the heater is above the main loop, but also I have a loop going to my trough heat, so maybe it helps keep the main loop primed per say? But I can see in his diagram that the heaters would never get starved from an air pocket....Although I've never had to add glycol in the 11-12 years I've had my system operating and it is closed loop. Hoping the video and the minor change I suggested makes sense...

BTW, I have my floor heat set to come on at 32° from the secondary output on the weepmiser. You have to remember, temps are coming down and slabs lose heat pretty slowly. So even at 32° (coming down) your floors will not freeze. Might save a little on gas usage! My slabs will stay ice free without FH even to temps down to about 25° with a warmer 40-45° day ahead of the freeze. I don't even turn my FH on till temps stay under 32° for a few days.

Primary-Secondary Pumping with Multiple Boilers - YouTube
 
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Sorry, reread your post and you mentioned controls. Basically the same way I have my controls set up. You are only controlling the main loop circulator and the pumps supplying glycol to the heaters...The inlet pressure to the heaters is what turns them on. So (Using relays of course to handle the load) at 32° the main circulator is energized and it pumps 100% of the time below 32°. On the return piping from the bays you'll have an aquastat monitoring the return glycol temp that is also energized from the same relay used to start the main zone pump. My aquastat has a 15° differential set so it energizes/starts the heater pumps at about 55° and shuts the pumps off at 70°....This setting on my system gives me 15 minutes on and 15 minutes off to keep from short cycling the heaters. The colder it gets, this cycle will change based on heat loss in the slab, but it automatically adjusts without changing a thing. The brilliant part of the system! Even down to minus 15 deg, my system cycles on and off meaning there is still capacity left! Every installation will be different. You have to make adjustments in the differential and output temp of the heaters to get the sweet spot about 5° above ice forming on the floors. You'll also need valves on each loop to adjust the floors of each zone so temps are as close as you can get them using an infrared gun. Its all part of the initial setup. Set it once and forget it. I haven't touched mine since I installed it! Hope this helps. Pretty easy and simple! BTW, I have a simple light switch inline to both the main circulator and heater pumps so its easy to over-ride the weepmiser. Like I mentioned, there are days where I know I can get by during a below 32° night without having the system come on automatically. If I want the system to come on automatically, I just tunr the switches on and let eht weepmiser do its thing!
 
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