Noob H2O Heater Q

Hi just signed up after finding this forum last night. Seen lotsa good advise already.

I'm preparing to install Hydronic under floor heating in my house and from the reading I've done at the Radiantech (sp?) site I understand that you can use a H2O heater to do the job. I intend to install an open/direct system and was wondering if my existing 40 gal (LP fired) heater would be up to the task of heating my 1150 sq. ft. home. I would of course ensure I used only potable rated components throughout. I have an open basement giving me full access to the entire underfloor, btw. I also downloaded the manuals to get a better understanding of the job and feel I'm up for it.

Thanks for your thoughts,

Tim from Maine

You need to do a heat load analysis to find out how much heat you need. If you search around the web, you can find a free calculator. It will require you to know the room sizes, ceiling height, exposure, window sizes, type, insulation and a few other things like how cold you want the system to be able to maintain a certain temperature...none of it is hard, but if you don't fill in all of the blanks, you won't get as good a result.

There is some concern on my part (and others) about having all of that water sit in the pipes in the non-heating season. I'd prefer a heat exchanger that would allow you to keep the two sections separate. Another problem is tempering the heat to the floor...you'd probably have to run the tank hotter than you want to have enough heat, but that may mean you don't need to run the stuff as long. This means that it may cycle a bunch. It is much more comfortable if you can run it constantly and at a lower temperature. Lots of things to consider.

I think you'd probably need a much larger tank or during a cold day, you'd never get a hot shower, either since the thing would be running constantly and not be able to recover.

Hydronic heat is a very comfortable way to go.

OK, HL Calc is driving me nuts. I keep coming up with a NEGATIVE net wall area. No matter how many ways and times I measure it up I keep coming up with gross wall area of 1120 sq ft and 1800 sq ft of window/door area. Now I ain't the sharpest tack in the box but I don't see how you can have more windows and doors than ya got walls for. I didn't measure any windows or doors twice (checked three times for that).

My window/doors in inches are;
40x54
74x54
28x38
72x80 (slider)
40x40
32x80
96x54 (pic window with two dbl hung sides)
68x80 (door w/ two side lites)
36x54
total
486x534=259,542/144=1802.25 sq ft
or 40.5x44.5=1802.25


The walls
24x46 ft foundation w/8' high walls. No overhang/cantelever so wall lengths are same as foundation.

24x2=48x8=384 sq ft.
46x2=92x8=734 sq ft
total 1120 sq ft of wall area

I have a Pensoti boiler (not installed) I can use but I want to take it with me to the place we're trying to buy. I'm only concerned about the operating temp being too much for the 7/8" PXC I'm going to use. The numbers I've run so far are telling me I need a fluid temp of about 150* for my application so maybe that's not a problem?

Thanks for the help,
Tim

not sure what your doing wrong but I come up with about 195.2 Sq.Ft. of window space.

Cass said:

not sure what your doing wrong but I come up with about 195.2 Sq.Ft. of window space.

Click to expand...

Thanks Cass! Makes way more sense than my result.

Math was never a strong subject for me but this one has me scratchin my head sumpin awful. Maybe one of the pros can show me the error of my ways.

Tim

Looks like you added all the heights, added all the widths, and multiplied those results to get the total area. Can't do that. Have to compute the areas individually and add them. I think there's a name for the rule in mathematics, but it's basically the fact that the sum of the products is not the same as the product of the sums.

Yup, that's what I was doing wrong alright.

Don't know if Cass missed a window or what but, I came up with 206.3 sq ft for a net wall area of ~914 sq ft.

Thanks guys,

Mikey said:

Looks like you added all the heights, added all the widths, and multiplied those results to get the total area. Can't do that. Have to compute the areas individually and add them. I think there's a name for the rule in mathematics, but it's basically the fact that the sum of the products is not the same as the product of the sums.

Click to expand...

Order of operations

PEMDAS - Perenthesis, Exponents, Multiply/Divide, Add/Substract.

Thanks Lakee,

Nice to hear from someone in the land of the pre-season #1 Buckeyes. I live in Maine but I still bleed Scarlet & Gray.

84 Grad of CTI, couldn't hack the math for the OSU engineering stuff.

GO BUCKS
2007 National Football Champs

40 gallon propane--no way -- ho zay

I am not a hydronics expert anymore

I used to do solar hydronics long, long ago

with potable water for both hydronic heating and batheing.....

it took two 75 gallon electric water heaters next to each other

and it was a frigging nightmare.........


So I can almost guaranetee

that a 40 gallon PROPANE hot water heater isnt going to cut it....

you will wear out that 40 gallon puppy in one season.....

it will constantly be on burning and burning just trying to keep up with

the intence demand on it...

then I dare you to try to take a bath
on a cold winter night and see what happens..........
your wife is not going to be happy at all......


doing a cost analysis with propane hydronics might be wise......

probably at least 75 gallon propane is in your future.....

with a 50 gallon back up storage tank next to it........


go big or stay home ---- if you have the room

Before you put hydronic heating under the basement floor, be sure that your heat loss analysis considers the losses into the earth. And if you ever get water up to the level of the tubing, the losses will be greater.

When my house was built in '64 the pipes connecting baseboard units were put under the concrete floor. The losses just in the copper pipe have caused me to change the system to avoid those losses.

With the cost of fuel these days you don't want to be heating the earth.

You speak of taking a boiler with you to a new place you are going to buy. I hope you aren't planning to leave this unconventional system to some unsuspecting new homeowner, along with the fuel costs. I would never buy a house with such a system, and I can't imagine that anyone doing a home inspection for a prospective buyer would recommend it.

I also have a concern about whether such a system without a barrier between potable and heating system water would meet code requirements.

Bob NH said:

When my house was built in '64 the pipes connecting baseboard units were put under the concrete floor. The losses just in the copper pipe have caused me to change the system to avoid those losses.

With the cost of fuel these days you don't want to be heating the earth.

Click to expand...

Oh, so that's where the global warming is coming from. Way to go Bob, look what you started!

Tim Clark said:

Thanks Lakee,

Nice to hear from someone in the land of the pre-season #1 Buckeyes. I live in Maine but I still bleed Scarlet & Gray.

84 Grad of CTI, couldn't hack the math for the OSU engineering stuff.

GO BUCKS
2007 National Football Champs

Click to expand...

Ya, go Bucks! I've got season tickets this fall. Can't wait! Don't you mean they'll be 2006 champs?

Ya, all that math was rough. I use very little of it these days except for the concepts. Always wondered why train drivers need so much math....

Ok, Back-to-back National Champs in 07?

The heat source is not decided yet, but already leaning away from the LP heater I have. I'll be doing more research on that. Whatever I go with it will be geared toward efficiency and increased sellability and yes, economy (mine). With the real estate market swinging toward a buyer's market (in my area at least) I want to add to the "I want that" factor as much as I can w/out killing my wallet.

My house is a Ranch w/a full basement, the heat tubes will be installed under the wood floor of the HOUSE not under the slab.

My parents' house (in Grove City) had the copper tubes in the slab for BB HWH and, big surprise, the system started leaking everywhere and they had to install a whole new system. Won't be making that mistake.