New Install Help Please

[Greatwhitewing]

In the springtime had installed Viesmann Vitronic 100 and Superstor 45 gallon indirect water heater. Shower is delta Carlisle rated at 2.5 + 2.5 GPM. Water heater on priority zone. Boiler has outdoor reset setback controls. Installed by very reputable contractor. Oil fired. WH was set to 130 and boiler temp varies.

First shower of 20 minutes with flow throttled back approx 60-70% of max flow and runs out of hot water and have to turn temperature ALL the way up. No other loads on DHW.

Had NONE of these issues during the summer months, plenty of hot water. Now the boiler is running for heat we have the shower problem. Had shower temp set in the middle at all times no matter how long the shower.

I was assured this set up would supply plenty of water unless really hot and really long showers back to back.

The contractor came by and made some adjustments with little or no change in performance.

Any ideas what to discuss with installer? This is not much better performance than I had with a 20 year old tankless POS.

[Furd]

Your description is a bit confusing.

Shower is delta Carlisle rated at 2.5 + 2.5 GPM

Do you mean you have TWO shower heads and each is rated at 2-1/2 gallons per minute?

If so, then THAT is the problem. A tank-type water heater can supply roughly 70% of its ultimate capacity before a noticeable drop in temperature occurs. That would mean that you have roughly 30 gallons of 130 degree water with it being cooled by the incoming water when in use. At 60% (of 5 gpm) flow rate you are using about 3 gallons per minute. Assuming that you are also mixing about 30% cold with the hot at the shower gives you an approximate flow rate of 2.1 gpm out of the water heater. That would be about 42 gallons in 20 minutes. Of course the heating supply from the boiler is going to offset the temperature drop from the tank somewhat but not likely enough to allow such flow rates for 20 minutes, especially if you do not have a priority control that (a) turns off space heating when using significant amounts of hot water, and (b) allows the boiler temperature to rise to full cut-out temperature; in other words, does not limit boiler temperature according to outside temperature.

The first thing I would do is to install a priority control (if you do not presently have such) and then raise the temperature of the heater to a minimum of 140 degrees (160 may be necessary) AND install a tempering valve at the water heater outlet to supply 130 degree maximum temperature water (125 may be safer) to the house plumbing. Starting with a higher temperature in the tank allows for more dilution with cold and reduces the flow rate out of the tank giving an effect of more hot water.

[jadnashua]

An indirect normally is setup with the boiler as a primary zone - this means that when it needs heat, it gets ALL the heat from the boiler. If so, then the thing should be setup to run full-fire, max temp to heat and reheat the indirect. Based on the size of the boiler and the size of the tank, the spec sheet should give you the first hour use. A properly setup indirect will normally provide LOTS more hot water than the equivalent sized self-contained unit (say NG, or electric), since the boiler has LOTS more BTU output than a typical WH.

Where I live, they REQUIRE a tempering valve on the outlet of any WH, regardless of how it is heated. With an indirect, they are normally rated to be set to maintain 140-degrees, and higher can be used, but anything above 120 should have a tempering valve to restrict the outlet to that. An exception is things like the dishwasher and washing machine which can clean better with hotter water (at least the DW, many people don't use hot in their WM).

[Greatwhitewing]

I wasn't quite sure how to interpret that 2.5 spec listed twice. Maybe someone who knows for sure can chime in. Bottom line is the flow is throttled pretty far back to to 50-75% of max flow.

The HWH is on the priority zone. Guy said it wasn't when he came but the initial install guys said it was. Not sure what to believe.

I have a tempering valve installed already.

Your description is a bit confusing. Do you mean you have TWO shower heads and each is rated at 2-1/2 gallons per minute?

If so, then THAT is the problem. A tank-type water heater can supply roughly 70% of its ultimate capacity before a noticeable drop in temperature occurs. That would mean that you have roughly 30 gallons of 130 degree water with it being cooled by the incoming water when in use. At 60% (of 5 gpm) flow rate you are using about 3 gallons per minute. Assuming that you are also mixing about 30% cold with the hot at the shower gives you an approximate flow rate of 2.1 gpm out of the water heater. That would be about 42 gallons in 20 minutes. Of course the heating supply from the boiler is going to offset the temperature drop from the tank somewhat but not likely enough to allow such flow rates for 20 minutes, especially if you do not have a priority control that (a) turns off space heating when using significant amounts of hot water, and (b) allows the boiler temperature to rise to full cut-out temperature; in other words, does not limit boiler temperature according to outside temperature.

The first thing I would do is to install a priority control (if you do not presently have such) and then raise the temperature of the heater to a minimum of 140 degrees (160 may be necessary) AND install a tempering valve at the water heater outlet to supply 130 degree maximum temperature water (125 may be safer) to the house plumbing. Starting with a higher temperature in the tank allows for more dilution with cold and reduces the flow rate out of the tank giving an effect of more hot water.

[jadnashua]

Raise the WH set temp to say 140-degrees and see what happens. You may want to lower the tempering valve setting to something around 120-degrees to prevent potential scalding issues. Also, the tempering valve may not be working well...it could be mixing in more cold than it should, masking that the tank really does still have hot water in it. While the water is being used, you might want to compare the pipe temp on the inlet and outlet of the tempering valve. Once the tank's temp drops below the setting of the tempering valve, it should not be mixing in any cold water and the inlet (hot) and outlet (tempered) should reach the same temperature. That info is probably available in the boiler's controller, but may be harder to find.

To check if it is a priority zone, one way would be to wait until one or more heating zones are calling for heat, then while that's still happening, exhaust the water tank to see if they stop getting heat. You may need to raise the room's thermostats temporarily to ensure they would still be calling for heat while the tank then needs it.

Also, ensure that the temperature sensor on the tank is inserted ALL the way into the well of the indirect...it is only held in by a spring clip, and may not be accurately sensing the temperature.

[Gary in NJ]

A zone controller with a DHW Priority would help greatly. Check out Taco's ZVC series.

As mentioned above, increase the water temperature. You want 130 at the tap, which will require 140-160 in the tank.

Finally, what size copper did the plumber use to pipe the HWH to the boiler? As a minimum it should be 1". If the plumber used 3/4 it will almost double the time for the HWH to recover.

[Dana]

You can measure your actual flow out of the showerheads with a bucket, a stopwatch and a measuring cup. Turn it on, put the bucket under it for exactly 30 seconds, then use the cup to measure how much water was in the bucket. A 2.5gpm head usually delivers between 1.8-2.2gpm unless you have unusually high water pressure.

A 20 minute shower is a bit on the long side. Not sure if simply cranking the temp is going to buy you much. Even the smallest oil boiler is going to be putting out 60KBTU/hr, which should be able to keep up with an endless shower if it's cut back to under 1gpm per head as-described. With 45F incoming water, 105F shower exit temp at a total 2gpm you're ~70KBTU/hr.

If the boiler's outdoor reset isn't set up to be over-ridden by the priority demand, and the boiler's output is held to a relatively tepid 150F because it's not very cold outside there may not be a big enough delta-T on the heat exchanger inside the SuperStore to deliver that much heat and the boiler will be cycling on/off during the shower even as the temp in the tank falls.

What's the BTU, gph, or kilowatt rating of the Viessmann?

[Greatwhitewing]

To Gary, the pipe from the boiler is 1 inch as well as the return.

Dana, the Viesmann is the smallest one with a Riello burner. I think 80k btu was the number???

20 minutes is a long time for a shower IMHO but it's the mother of my children, what can I do except complain a bit, a little bit. We did go over this with the contractor about somewhat longish showers.

I am now trying to figure how to determine WHAT my tank temp is set to. It's a Super-Stor and Honeywell controls. There is a disk inside that looks like it turns to adjust temp trip point but it's kind of blocked and hard for these old eyes to see.

It seems to me if have hotter water the draw is less per minute of shower. I don't know how all that plays with the reset control which works great for the heating so far.

[Dana]

80K isn't going to keep up with an endless shower at more than 2gpm at MA WINTERTIME incoming water temps, even if the boiler is allow to run hotter than the outdoor reset temp on calls for heat from the indirect. It was probably fine all summer when the incoming water was in the mid-50s or higher, but you're probably in the 40s now, and it may hit 35F some morning in late January or early February. But a drainwater heat recovery heat exchanger can make up for a lot:



Bigger/taller/fatter units return more heat than skinnier/shorter, but a 4" x 4' PowerPipe (tm) will return about half the heat from the drain water back into the incoming cold feed to both the shower and the indirect if you plumb it right. That gives you about 100-120KBTU/hr out of the hot water system to the shower, even though the burner is only supplying only 80K. Then US distributor for PowerPipe (a Canadian company) is EFI in Westboro, MA. You have to set up an account with them to buy off their commercial products listing, but they're pretty good about setting it up with a credit card over the phone.

Try cranking up the temp on the indirect first, since if that works it'll be the cheapest way out, but DWHR will pay for itself in short years with an endless shower (ab)user in the house if the price of oil average is the same or higher as it has been for the last 3 years, and it's cheaper than scrapping the indirect for a bigger on.

Got model names for the Honeywell on the SuperStor, and for the outdoor reset controller?

[master plumber mark]

your water heater is just too small ... only a 45 gallon unit will not keep
up with a 20+ minute shower your wife is taking.....it aint gonna happen

turn it up to 140,
put some shower arresters in the shower heads,
but just dont tell your wife. and see if she notices..

if she does notice and complains, then stand up for yourself...
Just grow a back bone, tell your wife how its gonna be
and lay the law down...you got to draw the line somewhere


.if this dont work, then
you probably need a 75gallon heater ......65 at the minimum
to keep peace in the shower

[Greatwhitewing]

Let's say I want to go bigger. Is there a downside to ADDING a tank or is replacement the only proper remedy? Two 45's would give me 90 (duh) and potentially a back-up..

your water heater is just too small ... only a 45 gallon unit will not keep
up with a 20+ minute shower your wife is taking.....it aint gonna happen

turn it up to 140,
put some shower arresters in the shower heads,
but just dont tell your wife. and see if she notices..

if she does notice and complains, then stand up for yourself...
Just grow a back bone, tell your wife how its gonna be
and lay the law down...you got to draw the line somewhere


.if this dont work, then
you probably need a 75gallon heater ......65 at the minimum
to keep peace in the shower

[Dana]

Decent sized drainwater heat recovery heat exchangers more than double the apparent capacity of the tank, save roughly half the fuel, and cost less than a 75 gallon indirect. Swapping tanks makes no sense- you'll get more showering HW out of the DWHR and your 45 gallon tank than out of a 75 gallon tank, in fact it'll be pretty much endless-shower time with 100% of the boiler output directed to the HW side (priority zoned indirect.) A bigger tank would only make sense if you had a big tub to fill. (You don't get the heat boost out of the DWHR in tub-fill, since there's no water flowing down the drain to recover during the fill phase.) Economics of fuel issue aside, it's still a better solution in terms of raw shower-time capacity.

I assume that the SuperStor indirect has the MA code-required tempering valve or thermostatic mixing valve on it's output, so you COULD go ahead and crank the storage temp up to 180F (IIRC, the upper bound operating temp of the SuperStor) if you like, keeping the output the tempering valve at 120F or less, but if the outdoor reset it inhibiting the high-temp it may not actually get there. Standby losses from the tank at 180F will be about double that of a 120-130F tank though.