NTI VMAX Plus - Combi unit - Can not keep up

ggch

I just had a NTI VMAX plus unit installed in our home. The hot water system cannot keep up with our needs. You may get away with taking one hot shower, but by the end of the first person talking a shower or definitely by the second person taking a shower the water goes luke warm. I had a Rinnai
endless hot water in my last house and never had a problem. This NTI unit is not endless hot water.
I am wishing I never agreed to go with a combination unit. Did I purchase the wrong brand?

Jamie Hall

I doubt you purchased the wrong brand, although I don't know much about that particular brand. However, did anyone ever do a proper load calculation on your heating and hot water needs to size the unit? Doesn't sound like it. And that's not the fault of the boiler -- that's the fault of the individual who decided what size to buy.

NYplumber

The NTI is a good manufacture that backs their product. We dont know which model vmax you have, how you have it installed, or the size of the shower head being used.
Post info and photos.

kcopp

Have you contacted the installer?
there may be a few adjustments to make to boost your hot water output.
Give us as much info about your home, water usage and the piping. yes pix are nice.

ggch

Ok, my home is a 1960's colonial with 3,900 sq ft with low ceilings. Total of 4 of us with up to 2 people showers at same time typical. All baseboard heating. Up state New York winters. Took out 2 hot water tanks and Boiler for this combo unit. I believe it has 110 BTU. Also, plan on adding radiant floor heating for kitchen when we redo this summer.

ggch

https://www.ntiboilers.com/products/vmax.html


https://www.ntiboilers.com/uploads/nti/pdfs/manuals/85171 Vmax Installation and Operation Manual.pdf

kcopp

That has a little 16 gallon built in indirect.... Not likely that it will keep up w two showers at the same time..... especially the 110k btu version.

hot_rod

A home of that vintage may have high flow shower heads. Take a five gallon bucket in the shower and time how long to fill the bucket. Then you have the gpm requirement of the shower(s)

If they are 3 gpm or more you could get low flow shower heads. Some of the new heads feel about the same as the older high flow but use 1.5 gpm or less. That may be enough to get you where you want to be. if you still need or want that initial 2 shower dump, you may need to add a take again.

Delta has some great low flow heads that are affordably priced.

That is the catch 22 of combi units, you size for heat load, or DHW load, they rarely match.

Seems like a 180,000 is about what most households are happy with for DWH tankless style.

ggch

If my home and needs were sized correctly what should we have purchased? Should I have gotten something that was at least 180,000? It also seems that the design of the NTI Vmax is flawed for a home like hours because the 16 gallon unit can not keep up.

Does NTI have a larger combo unit that we would have worked for us? Or should we not have gone with a combo unit? What do you recommend?

Tom_133

ggch,

Do exactly what Hot Rod said to do. That boiler should be able to do back to back showers without a problem unless you are using a lot of water. I install NTI and as was said earlier they are a great company, and will stand by their equipment. But, if the boiler was sized for DHW incorrectly thats not on them. Its like backing the family station wagon up to a 5 ton trailer, you're asking it to do more than it can.

kcopp

Before picking a unit I would have looked at your water use....
You say you had 2 tanks?
Is that 2- 40 gallon tanks?

I prob would have steered you toward a separate boiler and an indirect tank. Most likely a 50 gal w/ a mixing valve.

Again call the installer and have them come back to get this right.... I know I would not want a customer to be unhappy w/ a piece of equipment I just installed.

Henry

In Montreal, we stopped installing combo and instant hot water in 2006. Our water is down to 33F at the end of January. The local gas utility has been pushing combo units for the condo market. The utility's service diivision has 5,000 problems now. I would try to use 60 gallon indirect such as the HTP Super Store Pro SSP60. It will provide a buffer.

hot_rod

I think you can you can work with what you have. I have a 120 combi at my home. My wife did have to adjust her DHW expectations to fill the tub, it just takes longer to allow the heater to keep up.

Adding a 40- 60 gallon tank would probably cover your demand, but you should run some flow test to be sure.

If you go with a larger size you may get short cycling in heating mode.

Henry

The brochure shows a 58F temperatre rise for 205 GPH which is close to 3.4 GPM = 98,20 BTU. Meanwhile the manual has two pages on legionnella and warns to keep water at 140F minimum. The unt can then provide only 2 GPM at 140F.

hot_rod

Henry said:

The brochure shows a 58F temperatre rise for 205 GPH which is close to 3.4 GPM = 98,20 BTU. Meanwhile the manual has two pages on legionnella and warns to keep water at 140F minimum. The unt can then provide only 2 GPM at 140F.

I saw 3.8 gpm in the manual somewhere? The incoming water temperature will maybe drop in winter months depending on the source, that changes expected output.

Also some shower heads flow 5 gpm!

bob eck

When using a combi condensing gas boiler / water heater you really need to know domestic hot water GPM needs.
Like Hot Rod said check out the GPM your current shower heads are delivering. Then switch to low flow shower heads like 1.5 GPM. YES 1.5 GPM shower heads are great if you get the rite brand and model. I had Alsons 1.5 GPM shower heads when my daughters lived at home as teenagers and when home from college and they never once told me they were not getting enough water to was their very long hair. If you still think you are not getting enough hot water put in a 50 or 80 gallon electric water heater and connect the elements up so the elements will maintain tank temp. When showering you will have 50 or 80 gallons of hot water to start with.
Or you could run the hot water into a 50 or 75 gallon power vented gas water heater.
I work for a wholesaler and we sell many different brand condensing gas combi boilers but the installing contractor needs to ask questions about the home owners hot water needs and they need to come up with a GPM requirement that the home needs.
Personally I like condensing boilers and condensing combi boilers with a SS fire tube heat exchanger. Lochinvar just came out with their Noble combi condensing gas boiler with SS fire tube heat exchanger and blazed plate heat exchanger for making domestic hot water.
They have three size Noble combi boilers.
110,000 BTU input delivers 2.6 GPM domestic hot water.
150,000 BTU input delivers 3.6 GPM domestic hot water
199,000 BTU input delivers 4.8 GPM domestic hot water
If a home needs the higher BTU input boilers for their domestic hot water needs the contractor can down fire the heating side of this boiler and when their is a call for domestic hot water the boiler will still fire up to the highest BTU input for the domestic hot water needs.
The contractor needs to know what the home owner needs and plan accordingly as to what boiler or combi boiler to use.
The contractor also needs to work with the wholesaler and put their heads together to come up with the best solution for the home owner.

Henry

My shower head flows more than 6 GPM. At the Savoy in London, we had a rainforest 14 inch head . The exposed faucet had 3/4 inch connections. There was a sign: "Do not leave bath unattended!". The wife wanted that. I got a 13 inch diameter. I took out the flow restricter and drilled out the ball. My temporary 40 gallon gas unit would run out in two longuish showers. I now have a HTP PH100-55. We can have showers, the washing machine going as well as the dishwasher, all at the same time.

Paul48

@Henry
Californians are cringing!