Air Issues with new Indirect Hot Water

[__raj]

Hi,

Our older boiler (Well McClain PH66HE Oil) had an indirect hot water tank and associated piping installed. The indirect HW supply is plumbed to the same line only used for overflow and also a copper tank overhead(expansion?). All other supply to three zones goes throw another supply on boiler that also has an air release valve inline.

The return for indirect HW blends back in with the other zones.

The plumber keeps coming back and quickly releasing air. But its painful running out of hot water often.

Will running the heat help alleviate the air problems once that season comes in?

[jadnashua]

A properly installed/maintained system should not leak, either air or water. Any air that does get into the system should be purged automatically (ideally, anyways). ANd, that air should only be there on initial system startup, not continually. Make sure you have a properly working expansion tank, and that is what takes up the volume when the heating system cycles on (the water expands, and needs to go somewhere - if it can't go into the expansion tank, it will leak out). When the thing cycles down, the water contracts. If the expansion tank is shot, it can create a vacuum and suck air into the system. It is possible that a circulator pump could be injecting air if the seal(s) are bad.

I think that you have a leak somewhere that needs to be fixed. And, possibly a bad, or missing expansion tank.

[Tom Sawyer]

It can be a bear to get the air out of some indirect coils. Installing an automatic air vent on the indirect's return line will help.

[__raj]

A properly installed/maintained system should not leak, either air or water. Any air that does get into the system should be purged automatically (ideally, anyways). ANd, that air should only be there on initial system startup, not continually. Make sure you have a properly working expansion tank, and that is what takes up the volume when the heating system cycles on (the water expands, and needs to go somewhere - if it can't go into the expansion tank, it will leak out). When the thing cycles down, the water contracts. If the expansion tank is shot, it can create a vacuum and suck air into the system. It is possible that a circulator pump could be injecting air if the seal(s) are bad.

I think that you have a leak somewhere that needs to be fixed. And, possibly a bad, or missing expansion tank.

A very small leak did start on one of the existing small circulators just after this tank was installed. The expansion tank does not appear to be leaking but I would not be surprised if it does. Its a copper tank from ?????

This system is approach 30+ years old with the exception of new HW. Again the piping for Indirect HW that gets air bound is shared with the relief overflow and expansion. The bright red circulator is the new one.

Some so-so pics of this setup:

http://ramijundi.imgur.com/boiler

I have considered replacing this boiler but not sure how much savings I would incur. We burn 800 gallons oil/year just heating 1910 home with 2600SF. It appears to burn about 20 gallons/month in summer with new indirect HW.

[Tom Sawyer]

Who in the Christ installed that freekin mess, Hackmasters Inc? The reason you are getting air is because the meat head that installed it ran the supply line off the internal air separator in the boiler. That would be the tapping that the idiot also has the relief valve piped into. What a f'ing mess. The indirect should be piped off the boiler supply and return (see the manual or go to weil's site) The relief valve should be piped off the supplied tapping on the rear of the boiler. It is currently installed in a very bad place because any air in that pipe prevents the relief from operating correctly. The copper expansion tank should be removed and replaced with a #60 bladder tank ( scrap the copper tank, copper is running pretty high now ) Until the piping gets re-done you will continue to have air issues forever. Where are you in NH? I can probably steer you to someone that can straighten that mess out for you.

[Dana]

Don't candy-coat it for him, Tom, tell him what you REALLY think! :-)

_raj- You can come up with a pretty-good estimate of what a new system would save you by using the FSC (fuel savings calculator) downloadable from a link halfway down this page:

http://www.nora-oilheat.org/site20/index.mv?screen=home

Using that tool carefully can also determine the whole-house heat load which can allow you to "right size" the boiler, resulting in the highest possible efficiency.

With a right-sized (or smallest-sized, as the case may require) new-school oil boiler you can probably peel off 150-200 gallons of fuel use.

But new boilers are expensive. You'd probably get a higher return on investment out of a high-efficiency ductless mini-split heat pump (air conditioning + heating), and just adding an economizer control to the boiler, such as the Intellicon HW+. (For a discussion about how a mini-split economics relative to oil boilers see this thread. ) Assuming the boiler is 2-3x oversized for your actual heat load (which would be typical), you can expect about a 10-15% reduction in fuel use out of an economizer control. If you have high-mass radiation (big old radiators rather than fin-tube baseboard) you might use an "outdoor reset" type control instead for similar return. With this type of control an 80% boiler will run at least 70-75% efficiency (rather than 60-65%) even if it's monsterously oversized. Thats 10-15% reduction in fuel us for a ~$500 investment (installed price.)

But depending on your electrical power rates, a decent mini-split heat pump will cut the heating cost by 25-75% from the cost the current price of oil in an old-school boiler, at an installed price of under $5000 (assuming a single-head 20,000-24,000BTU heat pump.) They get excellent efficiency above 25F, pretty good efficiency down to about +10F, and OK-efficiency down to -10F (at least some models do.) A mini-split isn't likely to be able to handle 100% of the heat load (unless it's a small house with an open floor plan), but if you can push 2/3 of the heating load onto the mini-split, that's 2/3 of the heating bill that comes at a big discount, decimating the oil use, but boosting the power bill (but by less than the cost of displaced fuel use.)

But if you're fortunate enough to be on a natural gas main and have higher-than average electricity prices it can often be cheaper to heat with gas.

But maybe oil is going to fall back below $2/gallon for then next decade, eh? ;-)

[Tom Sawyer]

Unfortunately I see that kind of hack installation almost daily around here and it really pisses me off because some hack proably made decent money for that. Anyhooo........as for the Mini-Split option. We sell and install probably 3 a month and for A/C they are the bomb. Around here though, heating is not quite as efficient and though they advertise that they will operate at low temperatures the reality is a bit different. The biggest problem is that unless you go with a ducted system they only deliver heat to one area and around these parts most houses are either Colonial's, capes or ranches. None of which are particularly open in the floor plan department so getting circualtion is a problem. I heat and cool my camp with a mini and it works well but when the temp drops below zero it is marginal at best and the electric cost to operate is not great. Mitsubishi has come out with some new stuff though that from first looks should be impressive although the price is still very high. I think that as of now and barring dramatic increases in energy prices that in the North East, an oil fired boiler running in the high 80's to low 90's gives the best bang for the buck especially if they are equipped with temperaturature modulation controls which by the way are mandated for all new equipment manufactured after 2012 so you will be seeing everything come through with these controls. I have had very good results with the Buderus Logano series and have the BE in my own home with the logamatic control.

[__raj]

Thanks.

I pulled the boiler manual and it now all makes sense. Very frustrated.

[Dana]

I hear what you're saying about the heat distribution issue- with mini-splits open floor plans & high R walls work the best, and in places with sub-0F temps for a daily high it's not an all-the time solution. The Mitsubishi Hyper Heating units still have pretty good output at +5F. They're claiming (and meeting) 100% of rated output at +4F and they're claiming 70%+ of rated output at -13F (but I haven't tested 'em there.) It's a moving target, but there's some indication that the latest-revision Fujitsu's beat the the Mitsu- Hyper Heat units at sub-0F temps, but it's a small sample set, and the sample set I've seen is a single model, not across the entire line. Mid-winter sub-10F weather they may not have as-dramatic a savings over $3 oil, but at 20F+ it will be substantial. (The mean temperature for Manchester NH in January is about 23F.) Both Daikin & Mitsubishi have high-HSPF 3-head 2 ton multi-splits, which can help some of the distribution issues, but you're then talking ~$8-9K (almost the cost of a better Buderus. ;-) ) Ducted air source heat pumps can't touch the efficiency of the split systems due to the air-handler loading. (Hydronic air source heat pumps can be pretty good with low-temp radiant slabs though.)

The installed cost of a noo-skool Buderus with the better controls is going to run at least 2x the cost of a single-head 2-ton mini-split, and save what, 25-30% over a tuned-up 85% beastie-boiler with an economizer control? In most of southern New England the cheaper mini-split would save more cash, and would certainly handle the AC load far better (more quiet, and more cheaply) than window-shaker solutions.

This guy made out pretty well with a 2-ton Fujitsu- it beat the socks off his recent Buderus for operating cost:

http://blog.energysmiths.com/2011/03...h-the-new.html

But that's a fairly tight, decently insulated cape in a climate quite a bit warmer than central or northern NH. (Martha's Vinyard MA.)

[Dana]

In-re mini-split output & efficiency at lower temps, note the fairly flat output at intermediate compressor speeds at temps between ~5F-35F on the models tested (graphs p. 13-14):

http://neea.org/research/reports/E11...ab-Testing.pdf

Clearly both efficiency an output starts to fall at temps below 5F (see graphs p. 16-17)- don't count on a COP>1.3 running flat-out at -10F, but a COP of 2+ @ +10F is pretty much assured on the newer/better units.