Another tankless water heater replacing boiler thread

[OurTown]

We were going to replace the old 399,000 BTU boiler several years ago but never got around to it. We are doing a major remodel of our wash now and want the floor space for more equipment and chemical storage. If we put the 60 gallon stainless storage tank where the boiler is now then we can install a 199K tankless type water heater above it on the wall. The current boiler is overkill (I have been running it in stage one on the gas valve for years) for only three SS bays only using it for wax and soap and I'm sure the boiler is in the 80%-ish efficiency rating. The separate heater, pump and tank seems to make the most sense to me because you can replace each component separately and it utilizes my SS storage tank that is only 5 years old. It is not a heat exchanger type tank so keep that in mind. Lots of questions on this:

Should we run the tankless heater temp really high (130F?) and install a mixing valve to get the temp down (110F?) to the gravity pump feed tank? What mixing valve to use if we need a max of around 11 GPM flow to gravity tank?

Would you need some type of controller to kick on the circulating pump? Can any tankless water heaters do that? I though I saw that some had some type of remote. Maybe we just need a relay for the pump and my tank thermostat would would control that? Assuming we have a mixing valve with temps state above then should we set the tank stat to kick the pump on at 110F and off at just below the water heater set temp? (128F?)

What pump to use? Do these water heaters need some pressure to get them going? Would you try to match the highest flow that the heater can put out the max temp rise at the minimum expected inlet temp?

Years ago I found that some Navian heaters can be used in unrestricted mode (I think they call it commercial mode) and wonder if that would help with pump flow sizing. It does void the warranty though.

I'm sure I'll have more questions as answers come in. We are having a plumber do this but want to give him some direction. I'm just not sure how familiar he is with all this. Normally I do all the plumbing but we will have other inspectors in throughout our project.

 

[OurTown]

Another thing. Eventually we would like to replace the 20 year old 627,000 BTU floor heat boiler with something more space saving and efficient. We are reducing our floor heat square footage and will have around 2,000 square feet or so when finished. Thinking again of going with maybe two tankless water heaters. Maybe I'll start another thread on this later when the time comes.

 

[OurTown]

As a side note (because 2Biz may bring it up ) have you seen the new price of the HTK PH199-80? Yikes!

http://bostonheatingsupply.com/phoenixph199-80stainlesssteelngwaterheater.aspx

 

[Greg Pack]

As a side note (because 2Biz may bring it up ) have you seen the new price of the HTK PH199-80? Yikes!

http://bostonheatingsupply.com/phoenixph199-80stainlesssteelngwaterheater.aspx

Water heaters have gotten crazy expensive. I need to replace one and and standard rheem 199K BTU with about a 70 gallon tank is $5500 or so.

 

[OurTown]

Just as I expected. After meeting the plumber today he has to do some research on what I want. He seems like a very experienced plumber but maybe this is just not that normal of a scenario. That's why I'm asking you guys as some of you have done this.

 

[2Biz]

As a side note (because 2Biz may bring it up ) have you seen the new price of the HTK PH199-80? Yikes!

http://bostonheatingsupply.com/phoenixph199-80stainlesssteelngwaterheater.aspx

I have seen the price increase!! If my HTP ever goes belly up (unrepairable) I won't be replacing it. If the tank was still good, I'd plumb in a demand heater and call it a day! I wouldn't think it would be that hard to plumb in a pump. For my Takagi 199k for floor heat, I have 2 Taco 013's in series supplying glycol to the heater. I get 40 psi and about 6.6gpm flow at 105deg. Studying/Learning the flow chart for the heater you select is imperative! It will help you make sure you imstall the right size pump/pumps to create the necessary pressure and flow you are looking for.

 

[OurTown]

I have seen the price increase!! If my HTP ever goes belly up (unrepairable) I won't be replacing it. If the tank was still good, I'd plumb in a demand heater and call it a day! I wouldn't think it would be that hard to plumb in a pump. For my Takagi 199k for floor heat, I have 2 Taco 013's in series supplying glycol to the heater. I get 40 psi and about 6.6gpm flow at 105deg. Studying/Learning the flow chart for the heater you select is imperative! It will help you make sure you imstall the right size pump/pumps to create the necessary pressure and flow you are looking for.

How many square feet are you heating with the one heater? Today the contractor was tearing out the floor of our old auto bays and the floor heat tubing was in the very bottom of the slab. Pea gravel (bad idea), re-mesh directly on top of that (so it was basically useless), tubing directly on top of mesh, then 6-8" concrete. No insulation. Terrible in my opinion. No wonder Super Wash (the builder) installed a 627K BTU boiler for a 3 SS/2 IBA.

 

[2Biz]

How many square feet are you heating with the one heater? Today the contractor was tearing out the floor of our old auto bays and the floor heat tubing was in the very bottom of the slab. Pea gravel (bad idea), re-mesh directly on top of that (so it was basically useless), tubing directly on top of mesh, then 6-8" concrete. No insulation. Terrible in my opinion. No wonder Super Wash (the builder) installed a 627K BTU boiler for a 3 SS/2 IBA.

Sorry it took me so long to respond...I wanted to get you an accurate measurement. I suffer from CRS and Kept forgetting to take my 100ft tape with me! I heat 4 bays, total of 1860sq ft. One bay is an outside bay, no roof. The other three bays do not have doors, so completely open to the elements. Keep in mind my wash had a 350K boiler for the floor heat alone. AND another 350K boiler just to heat the bay HP water! WOW! I am doing it now with the HTP on low modulating at about 35K btu! Yea, I don't think when my wash was installed there was much information that the owners could find and NG was pretty cheap back then, so they just threw the power to it! One thing they forgot to consider was the short cycling and the "Condensing" effects (damage) it caused to a non condensing boiler! A lot of "Flying By The Seat Of Your Pants" happened during that time frame. My wash was built in the 60's! Sounds like yours is about the same?!

 

[OurTown]

Sorry it took me so long to respond...I wanted to get you an accurate measurement. I suffer from CRS and Kept forgetting to take my 100ft tape with me! I heat 4 bays, total of 1860sq ft. One bay is an outside bay, no roof. The other three bays do not have doors, so completely open to the elements. Keep in mind my wash had a 350K boiler for the floor heat alone. AND another 350K boiler just to heat the bay HP water! WOW! I am doing it now with the HTP on low modulating at about 35K btu! Yea, I don't think when my wash was installed there was much information that the owners could find and NG was pretty cheap back then, so they just threw the power to it! One thing they forgot to consider was the short cycling and the "Condensing" effects (damage) it caused to a non condensing boiler! A lot of "Flying By The Seat Of Your Pants" happened during that time frame. My wash was built in the 60's! Sounds like yours is about the same?!

I suffer from CRS sometimes.
We are going to go from about 3,600sq ft to about 2,000 after removing two heated floors/aprons from the old auto bays and adding one large one back that will only have heated entrance and exit aprons.
Because our tubing on the old SS bays are under 6" of concrete and no insulation I'm thinking we need two 199K or maybe 180K units.
Our wash was built in 2003 and had over 1,026,000 BTUs for the floor heat and SS bay hot water.

 

[OurTown]

I just looked at my drawings and did some calculations. It will be just under 2,500sq ft when done.

 

[Buckeye Hydro]

What are you doing for water treatment before your boiler or other heater?

 

[OurTown]

What are you doing for water treatment before your boiler or other heater?

Water softener.

 

[2Biz]

I just looked at my drawings and did some calculations. It will be just under 2,500sq ft when done.

Hmmmm, might be pushing it to only go with (1) 199K BTU tankless? (2) should do it with ease! Is there any price difference between a 180K and 199K? I just looked and the Takagi I used is a little over $1200 from SupplyHouse.com

BTW, I don't have heated aprons. I just use salt and it seems to work well.

 

[Overachiever]

FWIW I used two Takagi 199k's for my now 5 bay Super Wash.. I also have a loop running through the trough on the roof. I cheaped out and orphaned my 6th bay from floor heat, just using it to dry pit mud now days, but I plan to fix it eventually. Had I known upgrading the automatic and making things so much more energy efficient would have been so successful I would have spent the money to do it right at the time. Paid the car wash off this year, so it was well worth it!

Also really wish my exit apron on the automatic was like 3x longer, I think it's maybe only 15' currently, it's a total mess back there in winter. City made me remove the outdoor drains and I totally underestimated what they were doing. Daily pneumatic ice chiseling, absurd amounts of salt, and hot water, are the only thing that prevents all the cars from getting stuck at the exit, lol. My exits are north facing and don't get much sunlight.

Also had 8" of concrete with the floor heat on the bottom, without insulation, lol, not sure what they were thinking. I only had them do 4-5" when they poured the new concrete.

 

[OurTown]

FWIW I used two Takagi 199k's for my now 5 bay Super Wash.. I also have a loop running through the trough on the roof.

This is what I want to do. Did you use the old pump and reservoir? Do you have a separate pump for the trough heat? Did you reuse the old slab stat or go with different controls altogether? Could you put some photos up here?

 

[Overachiever]

This is what I want to do. Did you use the old pump and reservoir? Do you have a separate pump for the trough heat? Did you reuse the old slab stat or go with different controls altogether? Could you put some photos up here?

I'll try and take some photos when I'm over there tomorrow, it's definitely not pretty, but I used the taco pumps that 2Biz used.. 2 in series going up toward the takagis and another right before the manifolds to the bays. I have another small one on the pipe that goes up toward the roof trough. I tried my best to do the primary secondary configuration 2Biz spoke of in his post where some of the output from the takagi's mixes back in with the cold coming back to increase efficiency.

I didn't install a thermostat, lol, I don't think my old slab stat was working. I've got mine plugged into smart switches right now and just manually turn them on and off if I feel like saving more money, but 2Biz (or someone) told me I should use the weepmizer, which seems a lot more smart.

 

[mjwalsh]

A local wholesaler (Ferguson) is delivering a Navien NNFC250200H COMBI TANKLESS for us this afternoon. This will be our first encounter with anything tankless. There appears to be nobody here locally specifically factory trained 100% certified to install which has to be a bit of a caveat. The good news is their documentation looks thorough enough & also there is tons of what appears to be quality support via install & maintenance on YouTube that go back enough years & also current videos. There are even some pre-plumbed piping assemblies that make it less likely to overlook some technical pipe arrangement issue! I did also buy a Webstone (Nibco) pre-assembly that was specific to the tankless combi that I bought.

I could be wrong ... but I am hoping that springing for the slight more $ for the FIRE TUBE EXCHANGER vs the WATER TUBE EXCHANGER will be better for the long term for this type of smaller boiler. Navien has the option for either one.

 

[2Biz]

FWIW....My floor heat circuit is energized at 32° from the secondary output on the weepmizer. It powers a 30a relay that supplies power to (1) taco 013 zone pump and (2) taco 013's that supplies feed to the heater. I also use simple light switches in line to both pump circuits so I can manually over-ride a below 32° day or night. The heater is plugged in to 120v, so always in standby during winter months. Overachiever is right, the plumbing is called a Primary/Secondary system.

I do not have a seperate smaller pump that supplies glycol to the trough loop. It circulates just fine from the single 013 zone circulation pump. I also don't use a slab stat, I simply have a T-stat on the return piping from all the zones. It controls the (2) 013's to the heater. The t-stat is set with a 15° differential. To keep bays ice free, my heater is set to 105° output and the return T-stat controlling the pumps to the heater cycle on at 55° and off at 70°. Each bay has its own ball valve to fluctuate flow and is adjusted so you get all slab temps that are as close as possible using an infrared gun. Its a set and forget thing. Then the return t-stat setting controls the rest. Once set, it automatically varies the amount of on time v/s off time to keep the bays ice free no matter how cold out. At 32° mine has a 15 mninute on/15 min off cycle. At 15° OAT, it automatically changes to a 20 min on, 10 minutes off cycle. Basically allowing for the different heat load. Funny thing is its always on a 30 minute cycle! Even at 15 below, it still cycles on and off meaning it still has some capacity in the heater to keep the bays ice free and at the same temp.

All installations will be somewhat different on the actual settings of the return t-stat. If your bays are close to 32° (After normalized) and you have your t-stat set to kick on at 55°, simply raise the t-stat 5-10° and the slab will raise the same value. Like-wise if you need to dial it down. I chose 15° differential so my heater didn't short cycle. 15 min on/15min off seemed doable and has been for years now. I've never had to change any of the settings since installation.

 

[2Biz]

A local wholesaler (Ferguson) is delivering a Navien NNFC250200H COMBI TANKLESS for us this afternoon. This will be our first encounter with anything tankless. There appears to be nobody here locally specifically factory trained 100% certified to install which has to be a bit of a caveat. The good news is their documentation looks thorough enough & also there is tons of what appears to be quality support via install & maintenance on YouTube that go back enough years & also current videos. There are even some pre-plumbed piping assemblies that make it less likely to overlook some technical pipe arrangement issue! I did also buy a Webstone (Nibco) pre-assembly that was specific to the tankless combi that I bought.

I could be wrong ... but I am hoping that springing for the slight more $ for the FIRE TUBE EXCHANGER vs the WATER TUBE EXCHANGER will be better for the long term for this type of smaller boiler. Navien has the option for either one.

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.

 

[ShinePro]

Hey Our Town
Come see the one we just put in in Yellow Springs
IBC - price was not bad
Better than Navien
Very simple unit
Very happy so far!!!!