My guess, based on just some very limited work so far, suggests that investing in better airtightness and MVHR efficiency looks to be better value than investing in better doors, windows etc.

The windows are heavy, but do have pretty robust looking hinges. Having looked around at lots of different makes I've concluded that, for our needs, Internorm look to be about the best option. They have a triple glazed sealed unit, plus an extra unsealed exterior pane that can be independently opened. Between the outer pane and the triple glazed unit there is a space wide enough to take an internal Venetian blind.

The UFH frustration I can understand. I'm looking at needing around 15 to 20 W/m², which is way lower than most UFH suppliers are used to. I like the idea of a fast response time (a purely personal thing), so that Floore system sounds interesting. I'm currently reconsidering the idea of having UFH, as although I like the idea of unobtrusive heating, there does seem to be some benefit in looking at other options, like warm air heating when the heating requirements get this low.

Conventional wisdom suggests that warm air heating needs high flow rates and/or high air temperatures, but once you get the heating need down to only a few hundreds watts per room at most, then it looks like the balance changes. I still need to do more work on this, but suspect that, for a house that's around PassivHaus standard it may well be possible to use warm air heating quite effectively. Doing this would certainly save a fair bit of money over having to fit UFH.

Posted By: JSHarrisI still need to do more work on this, but suspect that, for a house that's around PassivHaus standard it may well be possible to use warm air heating quite effectively. Doing this would certainly save a fair bit of money over having to fit UFH.

I have a house that's far far away from Passivhaus that uses warm air heating - it works fine and is surprisingly quiet. It does need high flow rates, but keeping the velocity down keeps the noise down (as does using acoustic lining in the supply ducts). Using a heatpump also keeps the temperature of the air reasonable so you don't get burning dust smells nor a drafty feeling from the stratification. Plus, if you need it, you can run A/C too (which, in my climate, we do - though the A/C load is about 1/10 of the heating load). For what it's worth, airflow rating of my system is 1450 CFM (about 684litres/second). With a heat source of 10kW, the delta-T would be around 12.5C (so the delivered air would be at about 34C if the room temperature is 21C).

Paul in Montreal.

<blockquote><cite>Posted By: Paul in Montreal</cite><blockquote><cite>Posted By: JSHarris</cite>I still need to do more work on this, but suspect that, for a house that's around PassivHaus standard it may well be possible to use warm air heating quite effectively. Doing this would certainly save a fair bit of money over having to fit UFH.</blockquote>

I have a house that's far far away from Passivhaus that uses warm air heating - it works fine and is surprisingly quiet. It does need high flow rates, but keeping the velocity down keeps the noise down (as does using acoustic lining in the supply ducts). Using a heatpump also keeps the temperature of the air reasonable so you don't get burning dust smells nor a drafty feeling from the stratification. Plus, if you need it, you can run A/C too (which, in my climate, we do - though the A/C load is about 1/10 of the heating load). For what it's worth, airflow rating of my system is 1450 CFM (about 684litres/second). With a heat source of 10kW, the delta-T would be around 12.5C (so the delivered air would be at about 34C if the room temperature is 21C).

Paul in Montreal.</blockquote>

Thanks again, Paul. I'm impressed with that relatively low delta T of your system, it makes me think that warm air makes a fair bit of sense. My peak heating requirement is unlikely to exceed 2 kW, even in really cold weather. I need to do some more research into this, as warm air heating is still rarely used here, having received a lot of bad press back when all the systems were based on resistive electrical heating, I think.

Just for a giggle, and to highlight why different heating systems can work in one place and not another I had a look at the weather regime for Montreal. Salisbury has an annual mean temperature of 11.4C, Montreal 7.3C. The interesting bit to me anyway is that, if you look at when the temperature goes above and below 10C, Week 16 and 41 for Montreal and Week 17 and 46 for Salisbury, there is a 5 week difference. Also the Standard Error, which uses Standard Deviation, that is based on Variance shows a larger change when the heating season starts in Montreal. That should mean that, almost without exception, come Week 41 (second week of October) the heating will be on. Is that the case Paul (though your a tough Yorkshireman so maybe you last till November )

There are two main weather variations that dominate, one is the West to East and the other is the change in weather patterns (seems to happen every 5 days or so). We tend to notice the change in pattern most as this is more memorable, So we remember last winters bad snow, but are probably already forgetting about the dryness we had as that lasted longer and became the norm (we remember 1976 but not 1975 and there was not much between them).
Biggest difference between us and Canada is the ratio of landmass to water mass, the Atlantic is a great damper.

<blockquote><cite>Posted By: SteamyTea</cite>
Biggest difference between us and Canada is the ratio of landmass to water mass, the Atlantic is a great damper.</blockquote>

I think we may sometimes underestimate the effect that has. I worked in Nova Scotia (around 500 miles further south than southern England) on and off for a while and never got used to the bizarre weather there. In winter the temperature could change by 10 to 15 deg C in a single day, as the very cold, dry air mass from central North America wobbled a bit and shoved the warm, wet air mass coming up the Atlantic coast away. It was fairly common to go to work in the morning in fog or rain with an OAT of maybe 5 to 8 deg C and drive home in freezing winds of -5 deg C to -10 deg C.

One question is how is that going to work for you in heating the rooms which are on the extract side? I'm guessing kitchen, utility and most importantly the bathroom.

Posted By: JSHarrisThe layout is such that if I feed the warm air into the living room, hall and bedrooms at near floor level...

Aren't there minimum heights for inlets and outlets? To do with being able to crawl under the smoke, I think.

Posted By: JSHarrisIf I over-size the ductwork then I can fairly easily alter the system to increase air flow if I find that it's required. This would mean adding an internal bypass to the MVHR to recirculate some of the heated internal air via a secondary fan but I'm hoping this shouldn't be needed.

Good idea to over-size the ductwork while you have the chance. This will help keep the velocity low and thus keep the noise down. Warm-air heating systems (over on this side of the pond) are, of course, fully re-circulatory, though the supply side of the HRV can be tied into the "return" side of the air heating system, the HRV having its own dedicated exhaust. If you do this, though, then the main circulation system should run if the HRV is running.

Feeding the warm air supply at ground level is the usual practice here - though I have a mix - ground level on the ground floor and ceiling level on the upstairs. It doesn't appear to make much difference to the distribution pattern, but the air flow is sufficient that there really isn't any noticeable stratification. All the supply vents are located next to windows, too, to reduce drafts from the cooler glass surface. Of course, if you have 3g or 4g, then this is less of an issue.

For my system, the auxiliary backup is just a 10kW resistive heater - so max power is about 21kW when both the heatpump and aux are running at the same time. The maximum supply temperature, though, is in the mid 40C range, so below the "dust burning" threshold of around 50C. My worst case heatload is around 15kW at -23C outside, 21C inside - to that means the aux heat would only be on half the time at that temperature. Most of the time, it doesn't run at all.

Warm air heating works best with a relatively low delta T and enough supply to avoid stratification. The hated systems of old used far too high a delta-T giving burning smells and discomfort. For people over here that use forced air heated by fossil fuel in combination with an air conditioner is that the ductwork tends to be sized for the A/C (delta T of around 12C) which gives a much higher delta T for heating (and also because people like to use setbacks and have a fast response). With heatpump systems that do both heating and A/C things tend to be much better because the delta T is the same in both modes. Such systems are designed such that they run more or less continuously and don't use temperature setbacks (otherwise you energize the auxiliary heating).

Hope this helps,

Paul in Montreal.

Thanks Paul, your practical experience is invaluable. Right now I can design-in space for large ducts, just by increasing the width of a couple of internal walls, so it makes sense to do this anyway.

Much of the time I think my system would run with a delta T of less than 10 deg C, even with the low air flow rate. It's only for relatively brief periods that the delta T would rise to maybe 20 to 25 deg (I hope!).

Another attraction of going for duct heating, is that it also gives me the option to use the ducts for cooling in the summer. As I'll probably be using something like the Ecocent for DHW, I may be able to direct the cool exhaust air from this to the ductwork.

Ed, thanks for confirming that duct inlet/outlet height's not a problem - had me shuffling through the BR's for a few minutes!

<blockquote><cite>Posted By: SteamyTea</cite>
Am I right in thinking that in a house you don't legally have to worry about fire breaks in a ventilation system, ethically is a different matter.</blockquote>

AFAICS there's nothing in the BRs about fire breaks in ventilation ducts. Whether or not they make sense depends on the layout and duct size, I'd guess. Small cross section ducts, such as those typically used in MVHR systems probably don't create a significant risk of accelerating the spread of fire, I'd have thought, as there's probably a limit to how far up a duct of this size that a flame front could propagate.

There has to be a far greater fire spread risk from leaving internal doors open, or even having an open plan design of house.

Hi

The Microgeneration now do a complete spreadsheet
the file is too large to add

please email kotpat@btinternet.com andd will send u a copy

Is it the one that allows you to calculate room losses for heat pump sizing?