I’m in the early phases of designing a new house (well, the architect is, I’m just the one paying for it 🙂 and I’m wondering if I should go with a hot water recerculation system or the new D’mand system (that uses the cold water supply as a return line). I did read the promotional material on the D’mand, and it seems to be very competitive (cost, economy, etc).
As for anything “too good to be true” I wonder if it really works, and I would appreciate if anybody who has used it could share their experience (I seacrhed the archive and only found 2 references to D’mand)
Am I better off with a traditional system?
Replies
One more question to better frame my problem: one of the reasons why I'm considering the D'mand system, is because I'd like to use an instant water heater, and I don't think that a traditional recirculating instant hot water would work with an instant water heater, while the D'mand system seems to work better with it...
Thanks in advance
I've never heard of the D'mand system. I checked out the product through their website... I donno about it... Seems a little complex.
I have heard of Grundfos's system:http://www.grundfos.com/web/homeus.nsf/Webopslag/PAVA-593QHX
It seems a lot simpler than D'mand's. I'm probably going to get a Grundfos system for myself in the future.
If it's a new house, then I would go with a traditional recirculating system. I'm a little puzzled about using an instant hot water with a recirculating system. I can't think of a way that would work. If you have access to natural gas you could go with point-source heaters at each location you want hot water. However, consider your life-cycle costs as to buying multiple heaters and piping for them vs. a traditional hot water heater and recirculating system.
Without knowing more about your water needs and usage I'm just pointing out some things you might think about.
Those 'recirc on demand' systems seem simple enough in concept. I would expect them to be technically sound, and reliable. I think there are at least 2 other companies selling similar packages. The only real downside is the extra wiring, switch installation, and such. That, and having to press a button and wait a few seconds for hot water.
I doubt the energy savings is significant for a typical single family structure, when compared to a standard recirc setup with insulated recirc lines, a thermostat, and a timer (like the Grundfos package).
The purchase price is somewhat higher, and the installation is going to be more. I'm not a big fan of using the cold lines as the return as a shortcut. I like my cold water cold.
If your in the early stages of design, why not find a heating/cooling/plumber like Rich on TOH to make sure all the systems work to their best. i.e. short runs from water heater to faucet, equal length branches for the cooling/heating ducts. You might find you don't need to circulate hot water. 'cause you know thats going to be a energy loss. Don't get to hung up on payback vs cost, look for comfort and low running costs. Maybe two water heaters, one instant for the guest shower, standing type for the master tub.
Please forgive my ignorance, what's TOH? I'm assuming "This Old House" (I'm a newbie here :-).
Thanks for all the answers... here are more info: the house is (tentatively) a ~4,000 sqft construction on 3 levels, on a ~65x25 ft footprint. Powder room on the middle floor, 2 bathrooms on the upper floor. Small bathroom on the lower level, probably not worth plumbing for instant hot water, as the lower level (daylight basement) won't be used frequently enough to figure out how to get a pump to work "uphill". Kitchen is on the middle floor, too
I'm originally from Europe, and instant water heaters are the norm: they are more convenient (no limit on the amount of water), cheaper to operate and smaller (not an issue on a big house, but an issue in a tiny European apartment :-). So i'm naturally biased toward an instant water heater, even if I currently have a traditional heater in my house.
On a small European apartment, you get hot water in seconds, and you don't need recirculation. On a bigger house, as I discovered, it can take a few gallons to get hot water. And I hate wasting water (more than waiting).
I will definitely have a pro design the system in the best possible way, but I like educating myself and understanding the options (sometimes contractors might just go with what they know best and/or works best for them, and given I can still choose a contractor, knowing my options can help)
A traditional recirc system (coupled with a traditional water heater) seems like an expensive way to heat the house :-) probably it's not as bad as I picture it, but it seems to me that there would be a lot of heat losses in the system. The D'mand system (especially with an occupancy sensor) can probably save energy, while getting instant water. Or maybe just add complexity... I'm not really sold on that system (btw: what are the others?)
Multiple heaters are not really an option I'm keen on exploring now, as it will require extra plumbing and venting
Once again, thanks for your help
I think that the typical recirculating system runs a very low amount of water flow and might not trigger the on demand water heater, but I have not looked at the specs.
On demand heaters require a miniumum flow rate for the heater to start.
I looked at the spec's on the D'mand system and it appears that it pumps fast enough (8gpm) that it should not be a problem. But I would check with both then and the heater manufacturer to be sure.
" won't be used frequently enough to figure out how to get a pump to work "uphill". "
No problem. That is the advantage of pumps. You have pressure and you can make it go any direction that you want. It is only when limited to gravity that you have a problem.
"a ~4,000 sqft construction on 3 levels, on a ~65x25 ft footprint. Powder room on the middle floor, 2 bathrooms on the upper floor."
If you can site the WH on the middle floor, depending on the layout, you might make short runs to all of the locations and that will reduce the amount of water that is needed to be run.
"I'm originally from Europe, and instant water heaters are the norm: they are more convenient (no limit on the amount of water), cheaper to operate and smaller (not an issue on a big house, but an issue in a tiny European apartment :-)"
Also that small apartment problaby did not have 2 (plus) baths, powder room, dishwasher and clothes washer.
One big difference between the on demand and the storage tank heaters is the amount of hot water that can be run at the same time.
TOH is this old house.
4000 feet is a large house, so depending on the layout, short runs to the hot water heater might be tough. You could use another Euro type of set up depending on the type of heating you use. If your going to use hot air (not the best way to heat) then this won't work. If you have a "boiler" for radiant heat, in floor of wall mounted, then a storage tank with heating coil inside it would work very well. You could have two or three placed around the house for best use. Running costs should be low too. If this is a house for you to live in for ten to twenty years then getting it right from day one is very important. Most houses are built to sell so the builder is looking at bottom line and not running costs. Keep us up to date on this project.
Yes, 4000 sqft is very big (and we are trying to cut here and there), but it's a great lot with a beautiful view and, as much as we want to live there for a long time, we need to keep an eye toward resell value, especially because changing circumstance might force us to move back to Europe. We are trying to build what we like, but still keep an eye to what sells in our area.
Heating: that's a whole new story. We like "cycling the heat" a lot, as we like sleeping in acolder environment, and the house is empty for most of the day. As much as I don't like hot air (and I looked at the mini-duct systems, but I was discouraged), the main advantage of hot air is that it heats fast to the point where you are comfortable: think wakign up in the morning with hot air going while you eat breakfast and, as soon as you leave, the house gets back to a lower temperature, to get back up again in late afternoon. With a radiant heat system, the inertia is such that it's not efficient to cycle it. We are thinking of hot air + electric radiant for the master bathroom.
To answer another poster, small apartments in Italy (say, 1000 sqft) accommodate a family of 4, and have 2 bathrooms, kitchen, dishwasher and washing machine. The problem is that a water heater big enough to serve that family, takes up too much space. Concurrent use might be lower, but the overall amount of water used serially is not much less (well, most European dishwashers or washing machines use cold water). I still remember the days of the water heater in my home, and how after 2 showers you had to wait for 1 hour... instant water heaters (most homes now have a combination instant water heater, radiator heating furnace, combining the 2 functions, and requiring only one space, one flue, etc). Modern instant water heaters seem to work well. I also heard of hybrid systems where a very small hot water tank is paired to an instant water heater... maybe in that case traditional recirc works...
Keep the suggestions coming: I can use all the help I can get :-)
I ran a job where we put in hot water recirc with a Takagi (I think a T-K2 but I'm not sure). The pump that ran the recirc moved more water than the flow sensor for the heater required in order to start the heater (I think the heater required 1/2 GPM and we used a 2/3 GPM pump, a small Taco). The heater had a sensor on the incoming water and knew not to fire if the water was already hot. After the job the owner reported liking it fine.
The system that you might be able to use is a thermosiphon http://www.chilipepperapp.com/images/siphon.gif
No electricity is required, but most water heaters have a check valve in the nipples that have to be removed.