Tankless heater question

Phil_6

i have a customer who has an idea to install a tankless type on demand water heater and use it to feed into his existing gas water heater to increase the amount of hot water he gets by pre heating the incoming water into the tank to make it recover faster. The tank will then maintain the stored water until he needs it. I was wondering if anyone sees any drawbacks to this. Even a large tankless heater will fall short if he starts blasting the body sprays so he wants some storage.

thanks...Phil

Brian (Tankless)

Hi Phil

Advise your customer do it the other way round: preheat the water with the tank, and feed the tankless with warmed water. Less standby losses that way (lower delta T around the tank).

Make sure your choice of tankless (gas?) is FULLY modulating, and will modulate down as low as possible. The Takagi TH-1S (max 199,000btu) will flame-down as low as 19,000btu.

The T-M1 is 235,000btu (modulating) and will allow 9.6 gpm if installed this way. Or, two T-M1's in parallel with dispense with the need for the tank, and one may be disabled for service, while the other takes over.

Check out www.endlesslyhot.com or www.mytankless waterheater.com & talk with Darrel Thomas, he's one of the best out there regarding Takagi.

Give him my regards, and tell him Brian in Kinder sent you.

I have sold/installed hundreds of these units, and you couldn't pay my customers to take them out.

Best regards, and good luck.

Brian in Balmy 68* Swampland.

Phil_6

Piping the tank first..

Forgetting the standby losses which way do you think will make more hot water? With the tank first the tankless won't really kick in till the tank water cools off. With the tankless first if he starts using the hot water the tankless will kick in right away and the tank will fire up if the water goes out faster than the tankless can heat it. Or so were thinking. (Maybe it's the same thing) Just wondering

Phil

Jim M

tankless

In this application I would not put the tankless first. My experience is with Rinnai and as I understand it the Rinnai will limit flow in order to make supply water temperature. So if your customer is using a lot of hot water and the ground water temperature is low, the tankless will limit flow in order to make the desired water temperature. This will show up as low flow to the shower heads. Depending on budget, size multiple tankless water heaters based on total demand at the lowest incoming water temperature for your area.

Scott Gregg

Another thought

Jim M is right. If the tankless is first it can limit flow anyway.

What is the flow rate of the body sprays?

Take the total and use 80% to determine your hot water demand. I am a Noritz fan. In many cases you can use a twin system of 2 N-069Ms with the conecting cable and get 10GPM (more than that other then the cold spells) Two rennais will do the same thing. If your peak load is about 12-13GPM this would work great.

I hear good things about the "T" word but got tired of homeowners asking me why I charge "x" for one when they can buy it cheaper of the internet. That once or twice and lack of local support and I was done with them.

Brad_9

Side arm

I use a tankless as a side arm heater, ie: I pump water out of the storage tank, through the tankless and then back in. This requires an aquastat and circulation pump, but you get lots of hot water and no restriction in flow to the house at all. Has great recovery, almost continuous hot water if use is within the tankless rate. It's also more efficient than most gas water heaters, though you do still get standby losses. Make sure the storage tank is a well insulated model (at least 2" foam).

I did it because I have a coil in the lower half of the tank for solar, and heat only the upper half with the tankless, but you could use the whole tank for storage.