On demand hot H2O & tankless heaters
I need to replace my water heater(s). One’s leaking fairly good, the other seems OK right now, but…
Currently I have two 70 gallon gas tanks for a 4 bed, 3.5 bath single story house with two people. Both conventionally vented up thru the attic from the basement. They use a 6″ vent that also used to handle the furnace – since swapped out for a high eff, direct vent thru the wall. This ute room has two 6″ make up air vents coming in.
The house is somewhat squarish. On one side are the bedrooms and baths. Towards the inside of that side are the heaters. Way on the other side, as far away as they can get, are the kitchen and laundry.
The energy audit tells me if I were to swap these tanks out for a tankless model, I’d hit the 5 Star energy rating on the house (and if I did a few other things). He points out a direct vented model would allow me to plug those two 6″ holes in the wall.
But a tankless model would not save that much when I want the hot water in the kitchen and/or laundry. And it’s a pain sometimes now waiting for hot water in the baths even.
I’m liking this D’MAND system of recirculating by putting a crossover pump at the farthest sink. I’d need two or three. But I’m not all that thrilled about having to have some form of switch for the pump. Perhaps the motion detector option would be less of a hassle, but it could run quite a bit sometimes if the sink isn’t used, like when she’s putting on makeup. Making it’s use with a tankless somewhat questionable.
I could run a direct return line from the kitchen/laundry area, but not the baths. They’re DW’ed in.
Has anyone come up with a decent recirc system using tankless heaters that I could fit in under these conditions?
I’m thinking a recirc system will eliminate that bothersome low flow level problem.
Edited 9/19/2007 4:49 pm ET by peteshlagor
Replies
I would check out the possibility of putting in the tankless water heaters and augmenting them with small, electric tankless water heaters at the baths and the laundry. These would give you near instant-on, and they would cut off once the main hot water got there.
I also doubt that the recirculation hardware would help your flow problem. It won't bring water into the system any faster; it just moves the water that's there around.
peteschlagor,
All a recirc system will do is move hot water around . that way the pipes don't cool off and you don't need to flow a lot of cold water before the warm arrives..
That alone should give you an idea of what's happening.. the pipes are cooling off the water so it's constantly going to be heated with a recirc system. (even when nobody is using hot water).. bound to cost you more energy, not to mention the cost of the pump and it's energy.
To solve your flow problem just have a good size pipe to where each tankless water heater is then whatever pressure your house has you'll get out of your hot water faucet..
The shorter the run from a tankless water heater the hotter the water arrives at . perfection would be a tanless at each hot water faucet but of course that's silly.
My house the baths are on top of each other and only the kitchen is a bit of a run.. so I'd need two tankless heaters..
if the kitchen was on the back of the bathroom wall I could get by with one..
Total length wouldn't be over 10 feet and probably closer to 5 feet..not much water in a 5 foot piece of 3/4 inch pipe..
<<They use a 6" vent that also used to handle the furnace>>
Two on-demand heaters, one at each location, with appropriately-sized flues. I don't vent more than one device through a single flue.