How big of a hot water tank do I need?

[islandhopper]

I just bought a new house and it has radiant floor heating for a 20x40 ft area. They had a 10gallon hot water tank trying to heat this system. I have had the system on for over a week now and it's not heating up at all. When I close the thermostat the hot water tank actually heats up, so it's working, I just think it's not big enough, so my question is....

How big if a tank do I need for this?

Ryan

[Redwood]

New Home?

I'd make this part of a home warrantee issue...

Don't new homes have those?

[hawkins111]

floor heat

Ryan,

If the water heater heats up you have a problem with the circulating system. Valve closed, air in line, circulating pump? If the heater is an electric water heater I don’t see any efficiency there at all. It may be a simple system but costly. Since the house is new to you it may take a while for you to figure out the costs.

Good luck,

Tom

[islandhopper]

Tom,

The 10gal electric hot water tank only heats up when the water is not circulating (Ie: when I set the thermostat to below actual temperature of the room). When I turn the thermostat up the circulation pump allows the water to circulate and the 10gal tank cools off... over a 7 day period it did not get hot again with the water circulating, but as soon as the circulation stops it gets hot quite quickly.

I realize electric isnt efficient, would it be better to switch to a gas water heater?

Ryan

[islandhopper]

Tom,

If I went to a gas boiler system, how big of a gas boiler would I need for that area? Also, can I vent it (propane) to the existing furnace so I dont have to run a new vent line outside?

Thanks

Ryan

[HayZee518]

If it is a circulating hot water system, that is with the inlet water shut off, the return line from the system should feed the dip tube to the bottom element. heated water stratifies to the top of the tank. also, the area in cooled tubing that the heater supplies may be large and it will take several circulations to bring the temperature up five degrees.

[hawkins111]

bigger heater

Ryan,

A 10 gallon water heater is likely to be 110 volts. If this is the case you certainly do not have enough heating capacity. Roughly speaking, without knowing much about your 20x40 space or how much you want to raise the temp, you may need something in the order of 60K BTU’s. Your water heater may be only 7500 BTU’s. If these numbers are even close you can see you need a pile more heat? You could get someone to do the real math and size your water heater for your need. That may be easier than going to a different system. A gas water heater with a direct vent would work. You just need one that is big enough for the load.

Stay warm,

Tom

[islandhopper]

Tom,

This is great info, thank you! I KNEW this system wasn't big enough and I can't get a straight answer from the guy that built/sold me the place (he wont talk to us directly, but rather only through our realtors, etc) and the actual heating place that put in the system wont answer my phone calls.

Now it's lawyer time

Ryan

[islandhopper]

Also Tom,

I'm curious, how do I go about calculating how many BTU's I will need? I know you said 60k, but Im just curious how I can be more accurate here.

FYI: I just did an online calculator that converts from KW to BTUs, the system I have now is only 5118 BTU's , not even a 10th of what's required, OMG! The tankless system they had in before was marginally better and it was 16,000 BTU's...still not good enough though.

Thanks for your help, it's much appreciated.

Ryan

[hawkins111]

baseline info

Ryan,

I am not sure that a tankless heater is what you want. They get their efficiency from being on stand by for long periods of time. When they burn they really get with it. That is not what you want for a radiant floor system. You want something with a large mass of water. The calculations for heat lose are involved. Cubic footage, windows, insulation, doors, and temp rise. You can find a good one on line somewhere. It should include most things I mentioned. It will take you a bit to gather all the info. Once you have it it’s a snap. You may think about having a contractor come over and give you an estimate. Most of the time they don’t charge for that if you are really interested. You would then have a real idea what you are getting into.

Good luck,

Tom

[Redwood]

Tom,

This is great info, thank you! I KNEW this system wasn't big enough and I can't get a straight answer from the guy that built/sold me the place (he wont talk to us directly, but rather only through our realtors, etc) and the actual heating place that put in the system wont answer my phone calls.

Now it's lawyer time

Ryan

Exactly what I was talking about!