Energy penalty for hot water heater above hydronic system?
Hi all,
This question struck me lying in bed last night, and I was unable to find any answers online. Traditionally, boilers for hydronic heating systems are placed in basements to take advantage of the relative buoyancy of hot over cold water. For a modern, well insulated construction with heated floors, lower water temperatures and smaller temperature deltas are utilized, reducing the effect.
Assuming a homeowner is heating the slab of their well-insulated/sealed two-story home with a water heater placed in their (conditioned) attic, would there be a noticeable energy penalty compared to keeping the water heater on the slab? Would it matter if they were using well water?
Thanks,
Aedi
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Replies
You’re leaving out maintenance concerns. I’d keep all the mechanical equipment in the basement for ease of access alone. Hydronic systems generally use a circulation pump, so the relative bouancy of hot water doesn’t mater. I think you’re thinking of the thermosiphon systems used to recirculate domestic hot water without the need for a pump — those systems most certainly do require the placement of the water heater at the low point of the system.
Well water might make starting temperatures a bit less, but I’m not sure about that. I’d be more concerned with the mineral content of the well water and potential fouling issues of a hydronic system than I would be about any small energy consumption differences.
Bill
>"Traditionally, boilers for hydronic heating systems are placed in basements to take advantage of the relative buoyancy of hot over cold water. "
That is not really the case. It was only true for hydronic systems without pumps, the so called "gravity feed" boilers of 100+ years ago that relied upon convection to move the water in lieu of electric pumps. Once the power grid was pretty much everywhere pumped hydronic systems became the norm.
The more practical reasons for putting hydronic boilers in basements was that they were big fat heavy suckers. In the case of coal fired hydronic boilers there was the further issue of not having to carry the fuel upstairs.
Newer hydronic boilers (even cast iron boilers) are a lot smaller and lighter than those of even 40 years ago, and can be put pretty much anywhere. In tall buildings putting the boiler on the top floor allows you to run the boiler at a much lower pressure, since it doesn't have the water column of several stories of elevation bearing down on it, which puts less stress on the boiler, pumps, and zone valves, etc. In a 2 story that doesn't much matter- the minimum operating pressure of most boilers is about the same or slightly higher than a 2 story column of water. The pressure on the pipes in the basement might have to double from 12-13psi to 25-26 psi to keep the boiler at 13 psi, but pipes can take the higher pressure a lot more readily than other system components.
There is neither a significant energy penalty or advantage from putting the water heater/boiler in a conditioned attic compared to a conditioned basement.
Thanks for correcting my faulty preconceptions, and the extra information on tall buildings! I am surprised my information was more than a century out of date, but it happens to the best of us :). One less building science question to keep me up at night
If you've ever seen the massive size of the plumbing used for gravity feed systems it's easy to understand how pumped systems took over the market almost immediately. Moving the same amount of heat with a 3/4"-1" pipe with a pump is a lot cheaper and easier to install than the 4" -8" convective loop plumbing I've seen on some old gravity feed hydronic systems (most of which have since been converted with pumps & valves for better control.)