Tankless water heater installation

[DKAudio]

I don't need one but found a Bosch Aquastar (4.6 GPM) for $300, it has been mounted but is pretty much new. I was wondering how hard these are to install? My vent for the water heater is connected to the same one as my furnace. It is in the middle of my basement going straight up through the roof. I want to mount the tankless heater on the wall to get it out of the way. What are my options for venting this thing? Anything I should know about them? Your replies will determin if I am going to buy it or not. Thanks

[HayZee518]

is your furnace and the water heater both natural gas or propane? if one or the other then exhausting the burnt gases into the same flue is ok. you can't mix two different exhaust gases like a wood or coal stove into the same chimney flue as nat gas or propane.

[DKAudio]

They are both NG but the flue is about 6' away from the wall where I would mount the water heater, I can't vent horizontal then to a 90 and up, can I?

[HayZee518]

so go up at a 45 degree angle and a ninety into the flue. just remember heat rises.

[DKAudio]

That may be a problem. My basement ceilings are already pretty low (7' maybe).

No big deal, the guy isn't getting back to me like he said he would. I assume she is sold and gone.

[596]

Tankless water heater REQUIRE stainless steel flue pipe. If you download the installation manual from Bosch, it may also specify that it may not share a flue with any other appliance. Get that installation manual first. Are you also aware of the gas requirement? It requires a larger gas supply pipe than is typically found on a tank type heater.

[DKAudio]

Thanks, I believe my flue is galvanized. The guy must have sold it anyways, he never replied to me. Looks like I will be going with standard 40 gal again when mine dies. My whole basement is under ground level so I couldn't do a horizontal kit even if I wanted to. Oh well, new tanked water heaters have to be way more effecient than my 1980 40 gal (still going strong though, looks like new too).

Thanks

[pushkins]

I love the opening line to the original post " I don't need one, BUT, I found one" !!!

Ha ha ha .....sounds like me!

[DKAudio]

Why not eh? I am counting the days until my 1980 water heater goes...

[DKAudio]

Now I am looking at getting a Bosch Aquastar AQ125XNG. I can't find any info on it. Boschs website has the 125 Aquastar series but just BO and FX...

AquaStar 125B, 125HX, 125FX, 125BS Tankless Water Heater Models by Bosch

Does anyone know anything about this model? I would need to do a side vent for it and use my existing galvanized one just for my furnace. The problem is I built a deck that pretty much blocking where I would vent. I may be able to go past it but IIRC they say to go only 15' w/ a max of 2 90s; may not be an issue. I can't vent under my deck, can I (my deck is only 2' off the ground).

Do you need a power vent kit to do horizontal or is that just to increase length?



596 said that most tankless water heaters require a larger gas supply line than tanked ones, any idea what it is? I believe mine right now is 3/4" reduced to half.

[LazyPup]

The Bosch Aquastar125 series included the 125NG (natural gas) and the 125LP (liquefied petroleum).

Although the 125x series is now discontinued I did manage to find a downloadable copy of the installation manual in PDF format at:

Tankless Water Heaters from Bosch, Takagi Flash TKJr, TK3, T-M1 - fueled by Gas & Propane and Powerstream, PowerStar and Ariston Electric Tankless and Electric Mini-Tank Hot WaterHeaters and On Demand Water Heaters

In reviewing the manual I came across a number of details that would warrant attention.

PERFORMANCE:
The AQ125xng is rated for 3.7gpm @ a 45degF rise. Assuming you desire the maximum code rated hot water temp of 125degF the incoming cold water would have to be 85degF to achieve the maximum flow rate. This might be practical in mid summer in the Sunbelt where the water lines are buried rather shallow and the soil is heated by solar energy, however, in Northern climates where the water lines are buried a minimum of 6” below the average frost depth in mid summer we can expect the cold water to come in at the earths natural geothermal temperature of 50-55degF. On the other hand, in mid winter we can expect the incoming cold water to range in the 35 to 40degF range. With an incoming temperature of 35degF and a hot water calling temperature of 125 we have a 90degF differential, and at 90degF differential the AQ125xng is rated for a maximum flow rate of 1.8gpm. This may be okay for those such as myself who enjoy a moderate shower at around 90degF but for those who enjoy a very hot shower 1.8gpm will not meet the needs of even a water saver shower head (2.5gpm), not to mention the cold spike you that would occur if someone were to start the dishwasher, laundry or even wash their hands at a lavatory in another bathroom.

VENTING: (See Local codes)
The venting must be in compliance with the national gas code and all local codes for a category 1 appliance rated at 116,000btu.

Requires Type B (double wall) vent pipe.

The minimum vent height must be 6’ provided there are no elbows and the point of termination must be 2’ above any obstruction within a 10’ radius.

When a horizontal run of vent is required, the vent must have as much vertical rise as possible (minimum 12”) before turning horizontal.

All horizontal venting must have a ¼” per foot pitch upwards towards the exterior stack.

The maximum length of a horizontal run may not exceed 100% of the total vertical rise. (When a horizontal pipe is used to exit the structure, the length of the vertical riser stack on the exterior must be equal to or longer than the horizontal length.)

The vertical riser must terminate at a point at least 2’ higher than any obstruction within a 10’ radius of the point of termination and the top of the riser must be equipped with an approved weather cap.

GAS SUPPLY (PIPE SIZE):
The AQ125xng may be supplied by a ½” black iron pipe, provided the maximum developed length of the pipe from the gas meter to the water heater inlet does not exceed 10’. If the maximum developed length of pipe from the meter to the water heater is greater than 10’ but equal to or less than 40’ it may be supplied with a ¾” gas line and if the maximum developed length is greater than 40’ but less than 150’ it requires a 1” line.

This is assuming that the AQ125x water heater is the only appliance attached to the gas line.

When we have multiple appliances on a common gas line we must first total the BTU requirements of all gas appliances, then convert the BTU requirement to cubic feet of gas per hour.

By example; let us assume a house that has a gas furnace (150,000btu), A freestanding gas range in the kitchen (35,000btu), a gas laundry dryer (35,000btu) and the AQ125xng (116,000btu).

The total BTU requirement for the structure is then 336,000btu. The codes state that we are to then contact the local gas supplier and get the actual BTU/cu.ft value of the gas, but in instances when that information is not available we may use the average value of 1100btu/cu.ft

Dividing the total BTU requirement (336,000btu) by 1,100btu/cu.ft we get 305cu.ft

We must then compute the total developed length of pipe from the gas meter to the furthest appliance.

NOTE: The total developed length of the pipe is the actual length of the pipe including rises and drops plus the fitting insertion losses, which are expressed in lengths of pipe. By example, a ½” black iron pipe 90 elbow has an insertion loss equal to .8’ (9.5”) of pipe.

For illustration let us assume that the total developed length to the furthest fixture is 70’. Per IRC table T2413.4(1), With a load of 305cu.ft and an overall length of 70’ we would need to begin at the gas meter with a 1” pipe and continue running 1” until the first appliance tee’s off the line. From that tee we would deduct the BTU rating of that appliance, then compute the balance to cu.ft as before and determine the maximum developed length from that tee to the last fixture to determine the size of pipe from that tee to the next fixture tee. We then repeat the process again and again until we have sized all the pipes by the Cu.ft table.

MAINTENANCE REQUIREMENTS
Per instructions in the AQ125xng installation manual we must inspect the Main burner, Pilot Assembly, Water screen assembly, and vent assembly annually. The water valve must be lubricated at least once every 2 years and the water valve must be rebuilt one every 3-5years,

[DKAudio]

Thanks for the info, I did not take into account the starting temp of the water. My wife takes very hot showers/baths, maybe I will hold off on this one.

I do plan on getting a tankless eventually. I really want to get the water heater away from the center of our laundry area, it is pretty wasteful of real estate.

Like I mentioned, right now we have a 1980 40 gallon that cannot keep up very well. It does ok except for when my wife uses the shower, then I have to wait a little before I can.

Thanks again.

[LazyPup]

Do you have a basement?

[DKAudio]

Yes, not full 8' ceilings though. Probably around 7' or under to the joists.

[travisdecpn]

I know I may be coming in a little late on this one, but if you are going to mount a tankless unit in a basement, it needs to be a direct-vent model to pass code (and more importantly work correctly). You would be much better off to mount the unit on an exterior wall and use and outdoor unit. It's a little more involved since you have to move your piping and provide a 120V outlet, but you'll save a ton of money on venting materials.

As far as pipe size goes, the diameter required is determined by the distance from the source (most likely as gas meter for residential units) and the BTU demand of the unit. Most tankless heaters for a whole house will be in the neighborhood of 175,000 to 200,000 BTU's, quite a jump from 35,000-40,000 BTU's which standard tanked units demand.

A little off-topic, but most of Bosch's units use galv. Type B vent pipe, most other units from Takagi, Noritz, and Rheem require 4" Cat 3 S/S vent pipe. Bosch is actually making a line of tankless heaters that can be vented with 3" PVC which will be something to see. Hope this info helps.