A question about the Atwood XT hot water heater

[luvrbus]

I am helping the son in law change out the hot water heater in their MH and looking at water heaters the parts guy said the new Atwood XT would make 9 gals of hot water with a 6 gal tank and 16 gal with the 10 gal tank question being is this BS or fact any of you guys know anything about this new hot water heater    thanks

[WEC4104]

Sounds kinda screwy to me. My only guess is the guy is trying to give people some idea of how much water they will have at the temperature commonly used for washing dishes or taking showers.  Perhaps his twisted logic is that folks don't take showers with pure hot water, but rather use a mix with 33% cold in it.  So a 6 gallon water heater will be enough to provide 9 gallons of correct temperature water coming out of the shower head.  That's my best guess.

[Jeremy]

Sounds kinda screwy to me. My only guess is the guy is trying to give people some idea of how much water they will have at the temperature commonly used for washing dishes or taking showers.  Perhaps his twisted logic is that folks don't take showers with pure hot water, but rather use a mix with 33% cold in it.  So a 6 gallon water heater will be enough to provide 9 gallons of correct temperature water coming out of the shower head.  That's my best guess.

That is the correct explaination, but it's not really 'screwy' at all - many water heaters nowadays have valves on their output that automatically mix a proportion of cold water (set by the installer) with the hot water output of the tank itself to give a final output temperature that is correct for the person using the sink or shower. It's equivalent to having both a hot and cold water tap running together to end up with the water temperature you want, except it's done automatically for you.

Bear in mind also that you always get slightly more hot water out of a tank than it's capacity, because as soon as you begin to empty the tank it is already refilling and heating the new water. If you have an 'instant' hot water heater the water is heated fast enough that you will get a continuous flow of hot water no matter how long you leave it running.

Jeremy

[Dallas]

According to the google blurbs, he's right... kinda

http://engineering.marssociety.org/documents/Atwood_GE16EXT_water_heater_MPD_93758_9.10.04.pdf

[chazwood]

An instant water heater for a coach seems like a no brainer to me. Could I be missing something?

[Jeremy]

An instant water heater for a coach seems like a no brainer to me. Could I be missing something?

Because of the power required to heat the water that quickly, an electric instant heater isn't really an option. Gas is ok, and almost all UK caravans and motorhomes (for example) has gas instant water heaters as standard. Personally I wouldn't have gas in my bus, but obviously many do.

My own heating system is based around a large and well insulated calorifier (80 litres capacity) which will use the engine heat to heat up and store a large amount of domestic water, with a Webasto plumbed into the system as well. If everything is cold and I don't want to heat up the big tank there is also a small electric water heater that will provide enough water fairly quickly to fill a sink or have a shower.

Jeremy

PS. Has anyone else noticed that the 'gobussing.com' domain is down? For the last two weeks I though the forum was off-line until I realised I could get in by using 'busconversions.com' instead.

[chazwood]

By gas, you mean LP. Correct?

[pvcces]

chazwood, I think that the installation requirements for on demand hot water are fairly demanding, starting with a big enough flue and access to combustion air.

For a two gallon per minute flow rate, you need some 1500 BTU per MINUTE. That's a 90,000 btu per hour firing rate, or enough heat to heat a whole house in freezing weather, if it has any kind of insulation. And it has to have enough combustion air to keep up with it.

To avoid the problems that I just mentioned, most units produce much lower flow rates. The compromise between convenience and cost can be a real nuisance.

For what it's worth.

Tom Caffrey

[Jeremy]

By gas, you mean LP. Correct?

Yes, sorry, by gas I meant gas (usually propane in this case) rather than petrol. As it happens you can get petrol-powered versions of Webastos and Eberspachers (Eberspachers being badged as Espars in the US), which I suppose you might consider if you had a petrol-powered motorhome rather than a diesel-powered coach. And I won't mention Aquahot, because in the UK Aquahots are electric! Confusing isn't it?

Jeremy