Sizing Tankless Hot Water Boiler

[TapTapTap]

This year, I want to upgrade my small electric hot water tank in the kitchen side. I already have propane to the kitchen.

I want unlimited hot water for cleanup at the sink but also to run a hose into the evaporator room. I measured the sink flow at around 1 GPM. The hose could run at about 3 or more but could be regulated down and still have a good spray. I think a smaller unit in 100,000 BTU range could work. However, it seems like a 150 plus makes more sense for not a whole lot more money with better products available in that category.

Do others have a tankless and what size is it? Any opinions or suggestions?

Thanks
Ken

[maple flats]

Over the years I've had 3 tankless water heaters in my sugarhouse. The first one only heated 1 gpm up to 120F, from 35F incoming temp. It was good but my problem was that 1 gpm was not fast enough. I then took that one out and bought one rated at 3.3 gpm for 110F. That worked very well until one time I forgot to drain it. It froze and burst one tube (my sugarhouse is not heated unless the evaporator is boiling). Draining them is very easy and only takes about 30 seconds, I just forgot, at any rate, I tried to fix it using plumbers epoxy, it held for that season, but failed soon after. That was $220 in the trash. Soldering was considered, but I couldn't get the corner that had burst back close enough to even try soldering a patch on. vI then Googled and found several that were even better and at about 1/2 the cost. Made in China, but the others had all been made in China too. The first two were bought from Sportsman's Guide, the 3rd was not. My current one even has a built in digital thermometer (celsius only) and it works perfectly. I plumbed mine to use permeate and I pump it with a 115V diaphragm 3.3 gpm rated pump. When I don't have permeate I haul municipal water and use that. I have mine hooked up so it pushes the water into a cold line, then a tee with a ball valve to send water up to the heater, and another ball valve to get cold water at the sink. As hot water comes out of the heater I have a potable water hose connected, and a hot water valve to the sink. There is a drain plug on the heater but I learned it was not necessary when I tried to get a replacement O ring because the original started to leak. At the full line plumbing outlet I was at, the clerk said he knew exactly what that plug and damaged O ring was from, he had the exact same thing at his camp. He told me to just drain both the cold in and the hot out and the heater would be fully drained. That's how I've done it for about 5 years now, without issue. I don't seem to find a link right now, try a search on this site about tankless water heaters, I've linked to them a few times in the past. Mine cost about $105-110. What I find now are more than 2x that and up to well over $1000. Good luck.

[Wise Maple]

I saw Dave's hot water setup and liked it , I went thru e-bay and got one that says 18L min ,it hooks to a propane 20lb tank has the digital readout in celsius , and for around $170 it works pretty good , I plan to only run permeate thru it , Good luck with your project
Nelson

[TapTapTap]

Thanks for the input guys, I'll let you know what I end up doing. Hopefully I won't have a freezing problem ever again. I lost my original electric tankless heater from freezing when my hotdawg failed a few years back. I now have a temperature sensor with notification alerts if the temperature drops to near freezing so I'm hoping I can avoid that from reoccurring.
Ken

[maple flats]

Here's the one I have: https://www.amazon.com/VEVOR-Upgrade-Tankless-Propane-Regulator/dp/B07SYZ52N7/ref=sr_1_9?dchild=1&keywords=propane%2C+tankless+water+heater&qid=1620765458&sr=8-9
I don't know why it never showed in the same search when I posted the reply in #2 of this thread. When I bought it I paid $106.97.
It says, outdoor use only, but mine has been hung on my sugarhouse wall since I got my first one many yrs ago. My sugarhouse is well ventilated. If your's is tight, run the exhaust outside.

[minehart gap]

Ken, when I was getting mine, my son is a HVAC tech and had me talk to a rep. The rep did commercial work only and in a nutshell, he told me to size the on demand water heater at 2 times the size you need for your kitchen then go up one size more for RO closet. I may have more of a heater than I need but I never run out of hot water.

[TapTapTap]

Thanks everyone for you thoughts. My current plan is for 120k btu minimum but it depends on the manufacturer and it's not a big cost bump to go up one size. I'm planning to have it entirely professionally installed as I've done with my electrical work for piece of mind.

[bill m]

I am not sure if a 120k btu water heater will be big enough. Besides GPM you also need to consider rate of rise to get the water up to the temperature needed at a predetermined flow rate. If your sugar house kitchen is inspected by the board of health you will need a water temperature of 140 degrees minimum. When I was looking into an on demand system it calculated out to about a 190k btu water heater.

[TapTapTap]

I am not sure if a 120k btu water heater will be big enough. Besides GPM you also need to consider rate of rise to get the water up to the temperature needed at a predetermined flow rate. If your sugar house kitchen is inspected by the board of health you will need a water temperature of 140 degrees minimum. When I was looking into an on demand system it calculated out to about a 190k btu water heater.

Wow! 140 degrees and you get inspected by the board of health.

I agree that 120k btu is on the light side but I think it could work provided that the unit works at low flow. Output water temperature is all a matter of BTUs, flow, and water temperature coming into the heater. It looks like the rating that Maple Flats Dave has for his sugarhouse. An upsize unit would likely be in the 160k range and most residential home units start at 160 or 180 so that's where I'll be.

Ken