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Old 04-21-2009, 11:44 AM   #1
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Hot Water Heater for temporary Radiant


I'm in Iowa and we're building our own house one project at a time as money becomes available. We installed the pex before pouring the basement slab this past winter. This year we were planning on buying the boiler and setting up the radiant system so we could move in before this winter.

Because of some changes in the economic situation, we will now not have the money to do everything to get the house ready to move in by November (plumbing, electrical, drywalling, hvac, etc. etc.). Since most likely we won't be moving in, I was wondering if I could hook up an electric water heater to heat the house and keep it around 45F just to keep the house from freezing through the winter (especially the concrete in the slab).

We were looking into getting an 85 or 105 gal Marathon electric water heater for our house since electricity is a lot cheaper than propane (Plus it is cheaper getting it through the local coop). For heating, electric rates are half of regular rates as well.

Could something like that be possible to get us through this next winter? Then next year we can get the radiant components and hopefully we can move in then. It would be a closed loop system since we wouldn't need domestic hot water.

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Old 04-21-2009, 12:02 PM   #2
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Hot Water Heater for temporary Radiant


IMOP... Residential elec. water won't handle the task. Not designed to.

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Old 04-21-2009, 12:04 PM   #3
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Hot Water Heater for temporary Radiant


I'm not an expert at this, but I have radiant heat in my shop of about 2300 Sq. feet. I have a tankless water heater (propane) that runs alot in winter to keep the shop 50 degrees. I think you might be suprised how much electric you'll use, especially if it's an exposed basement & the house isn't completely insulated. Also, from my experience (paid HVAC contractor to install everything but insulation & tubing) alot of the cost of radiant is in the pumps, valves, switches, labor, etc.. In my case, the tankless WH was only about 20% of the total cost.
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Old 04-21-2009, 12:08 PM   #4
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Hot Water Heater for temporary Radiant


some tankless are designed for heating applications .. Some are not..This is per manfuacture instructions
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Old 04-21-2009, 12:37 PM   #5
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Hot Water Heater for temporary Radiant


Thanks for the replies. I had hoped that something could be done. The water heater is the one we will be using for domestic hot water. We can get the 105 gal Marathon for $275, so that is what we will be buying for the house. I just thought I could do a very simple setup to simply keep the basement from freezing. I don't need to have a fancy setup with all of the components. Jus the bare minimums to keep the basemet at 40F or 45F through one winter.
We may/may not have insulation in the main floor by then. We do have 1" R-board over the OSB upstairs on the exterior framing. The basement is ICF, so that is already insulated. Windows are already installed. We plan on doing closed attic, but can't foresee that done this year, but we're trying.
If we had to, we can cover the first floor with two feet of bubble wrap. (they throw it away by the truckloads near where I work), or figure some other away to trap the heat in the basement.
It is 1920 sq ft basement, there are 8 different zones in there, with most zones having two loops. Can't remember off the top of my head exact setup. I was thinking I wouldn't need to run all loops or all zones to get enough heat to keep it above freezing.
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Old 04-21-2009, 01:13 PM   #6
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Hot Water Heater for temporary Radiant


I'm not so sure there's anything real simple about radiant hook-ups. I just looked at my set-up, which is only 1 zone with 5 loops & this is what I came up with:

- heat source
- thermostat
- expansion tank
- backflow preventer
- pressure reg. valve
- some kind of mixing valve (I think?)
- circulating pump
- air bleed valve
- 2 spigots
- 2 valves
- 2 manifolds (1 adjustable for input)
- a heck of alot of supply/return plumbing

I would imagine all of this stuff is crucial for the operation of a radiant system. I would also deffinately run antifreeze in the system, considering the low operating temps & the fact that no one will be living there. 2 AAA batteries in the thermostat are all that's keeping the system from freezing otherwise. I would also have reservations about using a water heater for domestic water after it had the antifreeze in it. Again, i'm not an expert in this field, just some of my observations.
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Old 04-21-2009, 02:01 PM   #7
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Hot Water Heater for temporary Radiant


Here's another voice in the storm. I have been putting in radiant systems of many different sizes and configurations for the past 16 years and I can tell you right now you can not expect to maintain a 40 F temp in a 1900 sq. ft. concrete floor with an electric water heater. You could cross your fingers, toes, even your legs and pray, but if you left the heater running wide open (both 4500W elements on) all winter long and every zone hooked up, you might hold 33F at the concrete surface. As far as antifreeze goes, yes you do most definitely need it (50/50 mix with water) and you could use RV antifreeze, but after cooking it for a whole winter you would have to use a LOT of bleach to try to reclaim your water heater and I would not want to be the one to sample the water afterwards.
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Old 04-21-2009, 02:20 PM   #8
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Hot Water Heater for temporary Radiant


Thanks Jomama. You raise some good points. I might be better off plugging in a few heaters to do the same thing with less hassle. I just wanted to explore the idea.
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Old 04-21-2009, 02:31 PM   #9
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Hot Water Heater for temporary Radiant


Grampa Bud - thank you for your insight. That definitely does not sound like anything pleasant or worthwhile to figure out.

I will post again when I'm ready to do the system for real, so I can get some advice. We want to do most of the radiant install, if not all of it, ourselves. So we are still mainly learning about it.

I'm working on re-doing my heat loss calcs right now. Do I have to use the full version of the Manual J to figure out my loads? Or would the MJ8 abridged version be all right to use? The one at the library is the abridged version, but I can get the full version through inter-library loan if I need that. Thanks.
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Old 04-21-2009, 03:34 PM   #10
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Hot Water Heater for temporary Radiant


If this basement is mostly underground it might stay above freezing on its own providing the first floor is insulated and there is little air infiltration. The ground temperature 4' to 6' under the surface should be well above freezing so I think if you insulate the first floor and close off the basement it should stay above freezing without heat. A couple of electric heaters would be good insurance.

Rege

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