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stevenmarston 11-17-2010 04:28 AM

Sealed or vented?
Sealed or Vented? We want to hire a plumber to install a new heating and plumbing in our home. It seems that before we can get proper quotes or make progress, we have to make a fundamental choice between using a sealed or a vented system. It’s a large house (six bedroom), and we’re a large family of two adults and four teenage children, and our highest priority of all relates to water pressure. It’s vital that we can at least have a system which allows us to be running three or four power showers, at the same time, and not have the water temperature or pressure affected if someone then turns on a tap or the dishwasher starts up etc. Right now, this doesn’t work at all with our current system, even with one shower on, if a tap goes on too then we’re either scalded or frozen, or both alternatively.

I know little of the two system choices, other than the snippets I’ve picked up from plumbers so far. I’m told the advantage of a sealed system is no water tanks or pipework in the attic (so nothing to freeze), less risks of leaks going un-noticed and less risk of air locks (especially in an old house like hours where pipes do tend to go up and down a lot to get around the layout of the house), but with the disadvantage that cold water is based on mains pressure and the hot water only works on pressure, no pump like a vented system would have, so the more taps/showers that are on, the lower the pressure and the more likelihood of temperature changes when taps are turned etc. I’m told the advantage of a vented system is that the water supply to the showers will be from stored water (hot and cold) in the tanks, so constant pressure to all showers until the tanks run dry and much less impact of taps being turned on etc, but the disadvantages are tanks and pipes in the attic that can freeze, leaks can go un-noticed as no drop in pressure and higher risk of air locks…

How on earth am I supposed to make this decision which way to go? I only know I want us all to be able to have a shower without being scaled or froze when the dishwasher starts or one of us stops our shower (and of course I’d prefer not to have frozen pipes, leaks and airlocks). Can anybody help me shine some light on this, how to make the decision, are there other things to be considered, are there ways around the disadvantages of either solution? We really need help here…

Addition: Some replies I got asked about our current cold water pressure. I did a test, using the kitchen tap which is about as close to the mains as possible, I'm getting 10 litres per minute, though it's much slower if I go to the upstairs bathroom taps, less than half that.

immeraufdemhund 11-17-2010 02:28 PM

well your throughput can be affected by many things: corroding pipes, improper size of pipe, too many elbows in a system and the list can go on. Unfortunatlly you'll never have a perfect system.

I have to admit, though, that I have never heard of a sealed or vented water system. It usually only applies to drains and such. Unless you are referring to tankless or tanked water systems. I find that with tankless water systems your costs will be very high because of flow issues and quantity of heaters. With a large water heater though you have a different problem, it takes a lot of energy to heat up and maintain a 100Gallon water heater (sorry I don't know the litters, i guess 400L). Plus it's very heavy and probably based on the size of your house you'd need a recirculating pump. Which increases the costs of use.

Personally I'd go with tankless ONLY for small applications. We did a large house that had 4 showers and a sheet faucet that needed 10L per minute water flow. Even with 3 tankless water heaters we couldn't supply enough water to it, nor could the water heaters keep up with the demand. We had to put in a big tank and recirculate the water since it was so far from the heater.

That's my 2 cents though.

Homerepairguy 11-17-2010 02:51 PM


In your situation, I would have a homerun pex system installed. A homerun system has a large manifold (I think preferably near the water heater) with large diameter inlets (cold and hot) to each side of the manifold. Then smaller individual lines are run to each fixture. Homerun systems are touted as having the least amount of pressure drop to each fixture with minimal effect of simultaneous water usage.

Consider a minimum of 5/8" pex tubing to the tubs and 1/2" pex tubing to all of the other fixtures. Verify with your plumbing contractor that those size pex tubing will meet your "power shower" requirements. I would get a contractor that installs the Wirsbo/Uponer pex system since that system's fittings have a larger inside diameter than the crimp or cinch type fittings.

I would also request that pex joints only be made at the homerun manifold and the output fitting, which is how homerun systems should be installed. IOW, no elbow, T, or coupler joints in any line. No joints insure no posibility of leaks except at the manifold or output fixtures and also result in better water flow through each line.

Personally, I would not even consider installing a reservoir tank in the attic but that's just me. If you consider a tankless hot water system, be sure your a/c input power line to your home can handle even one tankless heater and for sure whether it can handle multiple tankless heaters running simultaneously. That alone will probably drop tankless from your options. Tankless heaters take a huge amount of electricity to heat water as the water is running.

Just what I would do in your situation,

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