Fiona Brick

Thanks for that. We're just at the point of going back over the pipes and doing further insulation. Thinking of overing with wool insulation and boxing them in with PIR. We have another section of the house where ducting is within thermal envelope and no issues with that vent air temp.

Hey, what changes did you make? We also have some of our duct work running through a cold attic space and we are experiencing really big temperature losses at the supply air points serviced by this duct work.

Effectively an installation issue then as the supplier/installer was the person doing all the duct work too?

Our estimated heat demand at the outset was expected to be 5kw during the coldest winter months. This was based on an airtightness test of 3.0 and a room temp of 21. We achieved an air tightness of 0.882, are A rated in terms of Insulation (ICF house) and took thermal bridging measures throughout the build. We have a vaulted space in the living room which was pointed out as being an area of concern. However, this isn't the area that is causing the issue. This area called for very slight additional heat during the cold snap we had but still maintained a steady temp of a min of 17. We are very open to putting an additional heat source here. The system itself has a 2kw integrated heat pump so in current weather conditions, it should be meeting our needs. However the area we are having issues with was never considered to be an area of concern by the supplier/installer. We were certainly never expecting it to be blowing cold air so frequently. My fear is that if it is an installation issue surrounding ducting or a mis calculation at design stage, supplementary heating will not address the issues in this section of the house as any supplementary heating will be counter acted by the constant flow of cold air and will end up costing an arm and a leg.

Ducting is by the same person, our supplier/installer.

Thanks for that John. This is exactly what I was thinking having observed and monitored the system in different operating states and external weather conditions. Thankfully the house is performing well so just need to get this aspect of things addressed by the supplier/installer.

I should have explained that the run from the machine to the areas where we are experiencing cold air is a relatively long run and passes through a cold attic. My guess is inadequate/poor insulation on the pipes and manifolds in the attic and/or a miscalculation at design stage of the heat loss per linear m. This is what I am requesting the supplier/installer to investigate and remedy. I guess what I'm trying to ascertain is, is it normal or to be expected in anyone's experience that there would be such a large temperature differential?

The MVHR unit has a counter flow heat exchanger and an integral 2kw heat pump. The integral heat pump heats the water and the supply air. Obviously as a 2kw system, we never expected it to meet out full heat demand albeit it wouldn't be far off. However the air supply temperature differentials in one part of the house v's the other is what is causing concern. Any additional heat sources will struggle when operating against an often constant flow of cold air. This is the issue we are trying to address and solve.

One MVHR. No post heaters. Yes, just air heating in standby when set temp is reached, ventilation still operating. This is currently our only heat source. We always knew we would need supplementary heating and we are looking into these options. However my concern is that in current circumstances the supplementary heating won't be kicking in and the bedrooms were emitting 9 degree air when going to bed last night. Were trying to figure out what we need to do. Thanks for your reply.

We have an MVHR unit installed in a new build - 220 sq. m, A rated house with an air tightness result of 0.882. The house is designed like two bungalows with a central hall. One section of the house is emitting cold air as low as 9 or 10 degrees when at the very same time the air being emitted by the vents in the rest of the house is 19 or 20. This happens when the machine is in standby due to reaching the required temp, when the system is in water heating and when the external temp drops below 8 or 9. The air being emitted in one section never really changes much while in one large section we are observing huge temperature differentials. It is a new system. We have gone back to the supplier and have been told this is normal, we should have expected this. What are your thoughts?