How is a Moisture Master supposed to work?

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BryanG

45 posts

Geek

#303224 25-Jan-2023 20:08

Hi all,

I have a 24 year old house which has an original moisture master installed. It has 3 switches - power on/off, heat on/off and fan low/high.

During the winter I usually just leave it on - and it keeps the windows nice and dry - we certainly notice it when we forget to turn it on!

Recently, on the Moisture Master website I saw that they can suck cool air in from the outside to assist with cooling the house.

The electrician I spoke to said that the ceiling space (which can get up to at least 53degs C) would heat the air as it passed through the ceiling space to the fan - so may not work for cooling.

Still, I pressed ahead wanting to try it and got him to install an external vent and duct leading to the fan in the ceiling. When he was here at 8am, I turned it on and it seemed to work well.

Now, the trouble is, I don't know when or how it turns on. I switched it on at the wall at about 3pm and nothing - no air coming in through the internal vent. It's been on all afternoon and now it's 8pm. In my mind, it should now be sucking cool air in from outside and blowing it into the centre of the house. But nothing. What normally triggers these things to start? It worked fine at 8am. Is it going to kick into life at 10pm?! I really wish it would just turn on when I flick the switch - but I assume it must have some sensor inside it disagreeing with me...

Can anyone advise? The electrician and I categorised this as a bit of an experiment - if I did get cool air coming out, I could then consider putting vents in all the rooms - with a new touchpad style controller. Maybe that's the issue? It still thinks it's a moisture master as we've only completed half the job? Does it have timer or sensor in the ceiling telling it when to turn on or off? I really want to see if we can get cool air inside before going ahead with the bells and whistles.

EDIT: It's now just come on at 8:15pm and is blowing nice cool air - about 2 hours too late but it's working.

timmmay

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#3027154 25-Jan-2023 20:16

Maybe it has a thermostat in it, stopping it pushing hot air into your house?

This might work, but you'll need a high volume of air to make a significant difference. It should help a bit, but probably not a lot.

We have ducted air conditioning, turned on from 2pm today, that pushes very cold air out, works well but as soon as I turned it off the temperature starts rising again.

BryanG

45 posts

Geek

#3027155 25-Jan-2023 20:29

Yeah - we looked at ducted a/c but it was around the $12k mark for 10KW. Thought I would try some wide open windows during the day (perks of WFH) and then some cool air pumped in during the evening.

It may well be a thermostat - will talk to the electrician. I planted a Zigbee thermometer in the exit-vent and it seems to have really kicked off at 25degs. Then in 18 minutes it's got down to 22degs. So that is a good result - but to be worth vents in each room, it would really need to start at about 6pm - which was still 31degs inside the vent.

tweake

2395 posts

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#3027161 25-Jan-2023 20:43

a lot of ventilation systems turn off when they are to hot. in summer, or even a sunny winters day, the ceiling can get to hot and it turns off. an external air inlet helps but at some point the heat is enough to heat soak the fan etc and it will turn off. the external air inlet helps extend the time it runs for.

most likely the reason you switched it on and nothing happened is that it was already turned off due to heat and it needs to be running to pull the air through it to cool it. so basically it needs to be running before it gets to hot.

i have a similar setup. it originally had manual change over from inside inlet to outside (press the button) but i made it automatic by adding a damper, thermostat and power supply. i set the thermostat (mounted in the ceiling) just above room temp so when ceiling space gets to that temp it switches to the outdoor inlet.

cooling ability? limited, because if it really hot the ceiling space is so hot it heat soaks the fan and it all turns off anyway. i would not bother to do it for cooling. i really do it to extend the run time to improve ventilation, after all its a ventilation system not a heating/cooling system. use the cooling system to do the cooling.

note: the only way to do it for cooling is mount the fan inside the house so it can't be overheated. but also keep in mind the outdoor air temp is not much cooler than the room temp anyway. very limited amount of cooling unless you have a house that gets crazy hot like the last place i lived in that hit over 40c inside.

timmmay

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#3027167 25-Jan-2023 21:11

With a high volume of air the ceiling cavity temperature becomes irrelevant, and the motor location only matters if that's where the thermostat is.

Putting 20 degree air into a 30 degree room that has a full room worth of furniture with all it's mass at 30c won't cool it much. Maybe it's enough to bother with if you don't want cooling.

Air conditioning is more effective. Yes it's expensive. Ducted systems really need individual room temperature control to be useful. Individual systems or multi split are simpler.

BryanG

45 posts

Geek

#3027174 25-Jan-2023 21:34

That all makes sense - thanks.

Ceiling space got up to 53degs on the day I measured it - so I guess that would convince the fan not to run. The inside of the house (on average) hits only about 30degs.

Now that the fan is actually running, the air flow is cool but quite weak - so adding another 3 bedroom outlets would make that worse. Plus I've been informed by the Mrs that each room would need to have control over the airflow (!!).

The sparky advised that the next step would be to add a damper and control panel - but it sounds (and feels) like all this would not be money well spent.

timmmay

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#3027178 25-Jan-2023 21:50

You would need a much higher power fan. I'm not sure it's worth the money either. Save up for air conditioning.

Hammerer

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#3027197 26-Jan-2023 02:22

It makes sense that that a large fan is needed to get a high air flow to improve cooling but we found a small fan works very well.

Last year we installed a small bathroom exhaust fan to pull air from under the eaves and send it 3m into a large room that can heat up really quickly in summer. We did this to provide fresh air and create positive pressure for a boarder who has difficulty opening windows. It is working as planned but the cooling effect is an unintended benefit. It gets the room temperature down at least 4C on very hot sunny days even though the intake is also on the hot/northern side of the house.

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Mattnzl

281 posts

Ultimate Geek

#3027216 26-Jan-2023 07:47

I've always thought my ventilation system would work better in summer if I could reverse it!

Crack a few windows on the south side, then the fans/ducting would draw hot air from up near the ceiling out into the attic.

Issues: would muck up the filters, fan blades are designed to operate best one way (but I'm sure they would still move some air).

mattenz

190 posts

Master Geek

#3027525 26-Jan-2023 14:37

We had a Moisture Master PPV system that I ripped out. The control panel has a summer mode button with a little light, is that lit up?

If it's on the same thermostat as the roofspace fan, that's going to be a problem. You should probably get a bit more acquainted with the system, those filters need changing!

BryanG

45 posts

Geek

#3027530 26-Jan-2023 14:45

All it has is power on/off, fan speed and heat on/off. And yep - I replace the filter each year.

It looks like it won't come on until the temperature in the ceiling drops to 25degs or less. Plus the fan is really too weak to make much of a difference.

If it could come on at 30degs and blow a bit more aggressively, it might just make a difference. But as pointed out, I should just save my pennies for a ducted a/c.

tweake

2395 posts

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#3027577 26-Jan-2023 16:49

BryanG:

That all makes sense - thanks.

Ceiling space got up to 53degs on the day I measured it - so I guess that would convince the fan not to run. The inside of the house (on average) hits only about 30degs.

Now that the fan is actually running, the air flow is cool but quite weak - so adding another 3 bedroom outlets would make that worse. Plus I've been informed by the Mrs that each room would need to have control over the airflow (!!).

The sparky advised that the next step would be to add a damper and control panel - but it sounds (and feels) like all this would not be money well spent.

ventilation should go to all rooms, simply because people shut doors.

one of the cheap methods is to do one outlet in the centre of the house. eg a hallway. however that can be a bit noisy as the entire flow goes into it. that may be what you have and you will need to keep doors open at all times to get proper ventilation. that kinda sucks as the ventilation usually ramps up at night when the roof cools down.

if you install ducted heat pump you can feed the ventilation into it and have the heat pump circulate it.